[PATCH] kexec: add kexec syscalls

This patch introduces the architecture independent implementation the
sys_kexec_load, the compat_sys_kexec_load system calls.

Kexec on panic support has been integrated into the core patch and is
relatively clean.

In addition the hopefully architecture independent option
crashkernel=size@location has been docuemented.  It's purpose is to reserve
space for the panic kernel to live, and where no DMA transfer will ever be
setup to access.

Signed-off-by: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Alexander Nyberg <alexn@telia.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 1080 insertions, 2 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index b01d26fe8db7..cfc8b0dea950 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -17,6 +17,7 @@ obj-$(CONFIG_MODULES) += module.o
 obj-$(CONFIG_KALLSYMS) += kallsyms.o
 obj-$(CONFIG_PM) += power/
 obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
+obj-$(CONFIG_KEXEC) += kexec.o
 obj-$(CONFIG_COMPAT) += compat.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
 obj-$(CONFIG_IKCONFIG) += configs.o
diff --git a/kernel/kexec.c b/kernel/kexec.c
new file mode 100644
index 000000000000..def9c73ec9a6
--- /dev/null
+++ b/kernel/kexec.c
@@ -0,0 +1,1036 @@
+/*
+ * kexec.c - kexec system call
+ * Copyright (C) 2002-2004 Eric Biederman  <ebiederm@xmission.com>
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2.  See the file COPYING for more details.
+ */
+
+#include <linux/mm.h>
+#include <linux/file.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/kexec.h>
+#include <linux/spinlock.h>
+#include <linux/list.h>
+#include <linux/highmem.h>
+#include <linux/syscalls.h>
+#include <linux/reboot.h>
+#include <linux/syscalls.h>
+#include <linux/ioport.h>
+#include <asm/page.h>
+#include <asm/uaccess.h>
+#include <asm/io.h>
+#include <asm/system.h>
+#include <asm/semaphore.h>
+
+/* Location of the reserved area for the crash kernel */
+struct resource crashk_res = {
+        .name  = "Crash kernel",
+        .start = 0,
+        .end   = 0,
+        .flags = IORESOURCE_BUSY | IORESOURCE_MEM
+};
+
+/*
+ * When kexec transitions to the new kernel there is a one-to-one
+ * mapping between physical and virtual addresses.  On processors
+ * where you can disable the MMU this is trivial, and easy.  For
+ * others it is still a simple predictable page table to setup.
+ *
+ * In that environment kexec copies the new kernel to its final
+ * resting place.  This means I can only support memory whose
+ * physical address can fit in an unsigned long.  In particular
+ * addresses where (pfn << PAGE_SHIFT) > ULONG_MAX cannot be handled.
+ * If the assembly stub has more restrictive requirements
+ * KEXEC_SOURCE_MEMORY_LIMIT and KEXEC_DEST_MEMORY_LIMIT can be
+ * defined more restrictively in <asm/kexec.h>.
+ *
+ * The code for the transition from the current kernel to the
+ * the new kernel is placed in the control_code_buffer, whose size
+ * is given by KEXEC_CONTROL_CODE_SIZE.  In the best case only a single
+ * page of memory is necessary, but some architectures require more.
+ * Because this memory must be identity mapped in the transition from
+ * virtual to physical addresses it must live in the range
+ * 0 - TASK_SIZE, as only the user space mappings are arbitrarily
+ * modifiable.
+ *
+ * The assembly stub in the control code buffer is passed a linked list
+ * of descriptor pages detailing the source pages of the new kernel,
+ * and the destination addresses of those source pages.  As this data
+ * structure is not used in the context of the current OS, it must
+ * be self-contained.
+ *
+ * The code has been made to work with highmem pages and will use a
+ * destination page in its final resting place (if it happens
+ * to allocate it).  The end product of this is that most of the
+ * physical address space, and most of RAM can be used.
+ *
+ * Future directions include:
+ *  - allocating a page table with the control code buffer identity
+ *    mapped, to simplify machine_kexec and make kexec_on_panic more
+ *    reliable.
+ */
+
+/*
+ * KIMAGE_NO_DEST is an impossible destination address..., for
+ * allocating pages whose destination address we do not care about.
+ */
+#define KIMAGE_NO_DEST (-1UL)
+
+static int kimage_is_destination_range(
+        struct kimage *image, unsigned long start, unsigned long end);
+static struct page *kimage_alloc_page(struct kimage *image, unsigned int gfp_mask, unsigned long dest);
+
+static int do_kimage_alloc(struct kimage **rimage, unsigned long entry,
+        unsigned long nr_segments, struct kexec_segment __user *segments)
+{
+        size_t segment_bytes;
+        struct kimage *image;
+        unsigned long i;
+        int result;
+
+        /* Allocate a controlling structure */
+        result = -ENOMEM;
+        image = kmalloc(sizeof(*image), GFP_KERNEL);
+        if (!image) {
+                goto out;
+        }
+        memset(image, 0, sizeof(*image));
+        image->head = 0;
+        image->entry = &image->head;
+        image->last_entry = &image->head;
+        image->control_page = ~0; /* By default this does not apply */
+        image->start = entry;
+        image->type = KEXEC_TYPE_DEFAULT;
+
+        /* Initialize the list of control pages */
+        INIT_LIST_HEAD(&image->control_pages);
+
+        /* Initialize the list of destination pages */
+        INIT_LIST_HEAD(&image->dest_pages);
+
+        /* Initialize the list of unuseable pages */
+        INIT_LIST_HEAD(&image->unuseable_pages);
+
+        /* Read in the segments */
+        image->nr_segments = nr_segments;
+        segment_bytes = nr_segments * sizeof(*segments);
+        result = copy_from_user(image->segment, segments, segment_bytes);
+        if (result)
+                goto out;
+
+        /*
+         * Verify we have good destination addresses.  The caller is
+         * responsible for making certain we don't attempt to load
+         * the new image into invalid or reserved areas of RAM.  This
+         * just verifies it is an address we can use.
+         *
+         * Since the kernel does everything in page size chunks ensure
+         * the destination addreses are page aligned.  Too many
+         * special cases crop of when we don't do this.  The most
+         * insidious is getting overlapping destination addresses
+         * simply because addresses are changed to page size
+         * granularity.
+         */
+        result = -EADDRNOTAVAIL;
+        for (i = 0; i < nr_segments; i++) {
+                unsigned long mstart, mend;
+                mstart = image->segment[i].mem;
+                mend   = mstart + image->segment[i].memsz;
+                if ((mstart & ~PAGE_MASK) || (mend & ~PAGE_MASK))
+                        goto out;
+                if (mend >= KEXEC_DESTINATION_MEMORY_LIMIT)
+                        goto out;
+        }
+
+        /* Verify our destination addresses do not overlap.
+         * If we alloed overlapping destination addresses
+         * through very weird things can happen with no
+         * easy explanation as one segment stops on another.
+         */
+        result = -EINVAL;
+        for(i = 0; i < nr_segments; i++) {
+                unsigned long mstart, mend;
+                unsigned long j;
+                mstart = image->segment[i].mem;
+                mend   = mstart + image->segment[i].memsz;
+                for(j = 0; j < i; j++) {
+                        unsigned long pstart, pend;
+                        pstart = image->segment[j].mem;
+                        pend   = pstart + image->segment[j].memsz;
+                        /* Do the segments overlap ? */
+                        if ((mend > pstart) && (mstart < pend))
+                                goto out;
+                }
+        }
+
+        /* Ensure our buffer sizes are strictly less than
+         * our memory sizes.  This should always be the case,
+         * and it is easier to check up front than to be surprised
+         * later on.
+         */
+        result = -EINVAL;
+        for(i = 0; i < nr_segments; i++) {
+                if (image->segment[i].bufsz > image->segment[i].memsz)
+                        goto out;
+        }
+
+
+        result = 0;
+ out:
+        if (result == 0) {
+                *rimage = image;
+        } else {
+                kfree(image);
+        }
+        return result;
+
+}
+
+static int kimage_normal_alloc(struct kimage **rimage, unsigned long entry,
+        unsigned long nr_segments, struct kexec_segment __user *segments)
+{
+        int result;
+        struct kimage *image;
+
+        /* Allocate and initialize a controlling structure */
+        image = NULL;
+        result = do_kimage_alloc(&image, entry, nr_segments, segments);
+        if (result) {
+                goto out;
+        }
+        *rimage = image;
+
+        /*
+         * Find a location for the control code buffer, and add it
+         * the vector of segments so that it's pages will also be
+         * counted as destination pages.
+         */
+        result = -ENOMEM;
+        image->control_code_page = kimage_alloc_control_pages(image,
+                get_order(KEXEC_CONTROL_CODE_SIZE));
+        if (!image->control_code_page) {
+                printk(KERN_ERR "Could not allocate control_code_buffer\n");
+                goto out;
+        }
+
+        result = 0;
+ out:
+        if (result == 0) {
+                *rimage = image;
+        } else {
+                kfree(image);
+        }
+        return result;
+}
+
+static int kimage_crash_alloc(struct kimage **rimage, unsigned long entry,
+        unsigned long nr_segments, struct kexec_segment *segments)
+{
+        int result;
+        struct kimage *image;
+        unsigned long i;
+
+        image = NULL;
+        /* Verify we have a valid entry point */
+        if ((entry < crashk_res.start) || (entry > crashk_res.end)) {
+                result = -EADDRNOTAVAIL;
+                goto out;
+        }
+
+        /* Allocate and initialize a controlling structure */
+        result = do_kimage_alloc(&image, entry, nr_segments, segments);
+        if (result) {
+                goto out;
+        }
+
+        /* Enable the special crash kernel control page
+         * allocation policy.
+         */
+        image->control_page = crashk_res.start;
+        image->type = KEXEC_TYPE_CRASH;
+
+        /*
+         * Verify we have good destination addresses.  Normally
+         * the caller is responsible for making certain we don't
+         * attempt to load the new image into invalid or reserved
+         * areas of RAM.  But crash kernels are preloaded into a
+         * reserved area of ram.  We must ensure the addresses
+         * are in the reserved area otherwise preloading the
+         * kernel could corrupt things.
+         */
+        result = -EADDRNOTAVAIL;
+        for (i = 0; i < nr_segments; i++) {
+                unsigned long mstart, mend;
+                mstart = image->segment[i].mem;
+                mend = mstart + image->segment[i].memsz;
+                /* Ensure we are within the crash kernel limits */
+                if ((mstart < crashk_res.start) || (mend > crashk_res.end))
+                        goto out;
+        }
+
+
+        /*
+         * Find a location for the control code buffer, and add
+         * the vector of segments so that it's pages will also be
+         * counted as destination pages.
+         */
+        result = -ENOMEM;
+        image->control_code_page = kimage_alloc_control_pages(image,
+                get_order(KEXEC_CONTROL_CODE_SIZE));
+        if (!image->control_code_page) {
+                printk(KERN_ERR "Could not allocate control_code_buffer\n");
+                goto out;
+        }
+
+        result = 0;
+ out:
+        if (result == 0) {
+                *rimage = image;
+        } else {
+                kfree(image);
+        }
+        return result;
+}
+
+static int kimage_is_destination_range(
+        struct kimage *image, unsigned long start, unsigned long end)
+{
+        unsigned long i;
+
+        for (i = 0; i < image->nr_segments; i++) {
+                unsigned long mstart, mend;
+                mstart = image->segment[i].mem;
+                mend   = mstart + image->segment[i].memsz;
+                if ((end > mstart) && (start < mend)) {
+                        return 1;
+                }
+        }
+        return 0;
+}
+
+static struct page *kimage_alloc_pages(unsigned int gfp_mask, unsigned int order)
+{
+        struct page *pages;
+        pages = alloc_pages(gfp_mask, order);
+        if (pages) {
+                unsigned int count, i;
+                pages->mapping = NULL;
+                pages->private = order;
+                count = 1 << order;
+                for(i = 0; i < count; i++) {
+                        SetPageReserved(pages + i);
+                }
+        }
+        return pages;
+}
+
+static void kimage_free_pages(struct page *page)
+{
+        unsigned int order, count, i;
+        order = page->private;
+        count = 1 << order;
+        for(i = 0; i < count; i++) {
+                ClearPageReserved(page + i);
+        }
+        __free_pages(page, order);
+}
+
+static void kimage_free_page_list(struct list_head *list)
+{
+        struct list_head *pos, *next;
+        list_for_each_safe(pos, next, list) {
+                struct page *page;
+
+                page = list_entry(pos, struct page, lru);
+                list_del(&page->lru);
+
+                kimage_free_pages(page);
+        }
+}
+
+static struct page *kimage_alloc_normal_control_pages(
+        struct kimage *image, unsigned int order)
+{
+        /* Control pages are special, they are the intermediaries
+         * that are needed while we copy the rest of the pages
+         * to their final resting place.  As such they must
+         * not conflict with either the destination addresses
+         * or memory the kernel is already using.
+         *
+         * The only case where we really need more than one of
+         * these are for architectures where we cannot disable
+         * the MMU and must instead generate an identity mapped
+         * page table for all of the memory.
+         *
+         * At worst this runs in O(N) of the image size.
+         */
+        struct list_head extra_pages;
+        struct page *pages;
+        unsigned int count;
+
+        count = 1 << order;
+        INIT_LIST_HEAD(&extra_pages);
+
+        /* Loop while I can allocate a page and the page allocated
+         * is a destination page.
+         */
+        do {
+                unsigned long pfn, epfn, addr, eaddr;
+                pages = kimage_alloc_pages(GFP_KERNEL, order);
+                if (!pages)
+                        break;
+                pfn   = page_to_pfn(pages);
+                epfn  = pfn + count;
+                addr  = pfn << PAGE_SHIFT;
+                eaddr = epfn << PAGE_SHIFT;
+                if ((epfn >= (KEXEC_CONTROL_MEMORY_LIMIT >> PAGE_SHIFT)) ||
+                        kimage_is_destination_range(image, addr, eaddr))
+                {
+                        list_add(&pages->lru, &extra_pages);
+                        pages = NULL;
+                }
+        } while(!pages);
+        if (pages) {
+                /* Remember the allocated page... */
+                list_add(&pages->lru, &image->control_pages);
+
+                /* Because the page is already in it's destination
+                 * location we will never allocate another page at
+                 * that address.  Therefore kimage_alloc_pages
+                 * will not return it (again) and we don't need
+                 * to give it an entry in image->segment[].
+                 */
+        }
+        /* Deal with the destination pages I have inadvertently allocated.
+         *
+         * Ideally I would convert multi-page allocations into single
+         * page allocations, and add everyting to image->dest_pages.
+         *
+         * For now it is simpler to just free the pages.
+         */
+        kimage_free_page_list(&extra_pages);
+        return pages;
+
+}
+
+static struct page *kimage_alloc_crash_control_pages(
+        struct kimage *image, unsigned int order)
+{
+        /* Control pages are special, they are the intermediaries
+         * that are needed while we copy the rest of the pages
+         * to their final resting place.  As such they must
+         * not conflict with either the destination addresses
+         * or memory the kernel is already using.
+         *
+         * Control pages are also the only pags we must allocate
+         * when loading a crash kernel.  All of the other pages
+         * are specified by the segments and we just memcpy
+         * into them directly.
+         *
+         * The only case where we really need more than one of
+         * these are for architectures where we cannot disable
+         * the MMU and must instead generate an identity mapped
+         * page table for all of the memory.
+         *
+         * Given the low demand this implements a very simple
+         * allocator that finds the first hole of the appropriate
+         * size in the reserved memory region, and allocates all
+         * of the memory up to and including the hole.
+         */
+        unsigned long hole_start, hole_end, size;
+        struct page *pages;
+        pages = NULL;
+        size = (1 << order) << PAGE_SHIFT;
+        hole_start = (image->control_page + (size - 1)) & ~(size - 1);
+        hole_end   = hole_start + size - 1;
+        while(hole_end <= crashk_res.end) {
+                unsigned long i;
+                if (hole_end > KEXEC_CONTROL_MEMORY_LIMIT) {
+                        break;
+                }
+                if (hole_end > crashk_res.end) {
+                        break;
+                }
+                /* See if I overlap any of the segments */
+                for(i = 0; i < image->nr_segments; i++) {
+                        unsigned long mstart, mend;
+                        mstart = image->segment[i].mem;
+                        mend   = mstart + image->segment[i].memsz - 1;
+                        if ((hole_end >= mstart) && (hole_start <= mend)) {
+                                /* Advance the hole to the end of the segment */
+                                hole_start = (mend + (size - 1)) & ~(size - 1);
+                                hole_end   = hole_start + size - 1;
+                                break;
+                        }
+                }
+                /* If I don't overlap any segments I have found my hole! */
+                if (i == image->nr_segments) {
+                        pages = pfn_to_page(hole_start >> PAGE_SHIFT);
+                        break;
+                }
+        }
+        if (pages) {
+                image->control_page = hole_end;
+        }
+        return pages;
+}
+
+
+struct page *kimage_alloc_control_pages(
+        struct kimage *image, unsigned int order)
+{
+        struct page *pages = NULL;
+        switch(image->type) {
+        case KEXEC_TYPE_DEFAULT:
+                pages = kimage_alloc_normal_control_pages(image, order);
+                break;
+        case KEXEC_TYPE_CRASH:
+                pages = kimage_alloc_crash_control_pages(image, order);
+                break;
+        }
+        return pages;
+}
+
+static int kimage_add_entry(struct kimage *image, kimage_entry_t entry)
+{
+        if (*image->entry != 0) {
+                image->entry++;
+        }
+        if (image->entry == image->last_entry) {
+                kimage_entry_t *ind_page;
+                struct page *page;
+                page = kimage_alloc_page(image, GFP_KERNEL, KIMAGE_NO_DEST);
+                if (!page) {
+                        return -ENOMEM;
+                }
+                ind_page = page_address(page);
+                *image->entry = virt_to_phys(ind_page) | IND_INDIRECTION;
+                image->entry = ind_page;
+                image->last_entry =
+                        ind_page + ((PAGE_SIZE/sizeof(kimage_entry_t)) - 1);
+        }
+        *image->entry = entry;
+        image->entry++;
+        *image->entry = 0;
+        return 0;
+}
+
+static int kimage_set_destination(
+        struct kimage *image, unsigned long destination)
+{
+        int result;
+
+        destination &= PAGE_MASK;
+        result = kimage_add_entry(image, destination | IND_DESTINATION);
+        if (result == 0) {
+                image->destination = destination;
+        }
+        return result;
+}
+
+
+static int kimage_add_page(struct kimage *image, unsigned long page)
+{
+        int result;
+
+        page &= PAGE_MASK;
+        result = kimage_add_entry(image, page | IND_SOURCE);
+        if (result == 0) {
+                image->destination += PAGE_SIZE;
+        }
+        return result;
+}
+
+
+static void kimage_free_extra_pages(struct kimage *image)
+{
+        /* Walk through and free any extra destination pages I may have */
+        kimage_free_page_list(&image->dest_pages);
+
+        /* Walk through and free any unuseable pages I have cached */
+        kimage_free_page_list(&image->unuseable_pages);
+
+}
+static int kimage_terminate(struct kimage *image)
+{
+        if (*image->entry != 0) {
+                image->entry++;
+        }
+        *image->entry = IND_DONE;
+        return 0;
+}
+
+#define for_each_kimage_entry(image, ptr, entry) \
+        for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE); \
+                ptr = (entry & IND_INDIRECTION)? \
+                        phys_to_virt((entry & PAGE_MASK)): ptr +1)
+
+static void kimage_free_entry(kimage_entry_t entry)
+{
+        struct page *page;
+
+        page = pfn_to_page(entry >> PAGE_SHIFT);
+        kimage_free_pages(page);
+}
+
+static void kimage_free(struct kimage *image)
+{
+        kimage_entry_t *ptr, entry;
+        kimage_entry_t ind = 0;
+
+        if (!image)
+                return;
+        kimage_free_extra_pages(image);
+        for_each_kimage_entry(image, ptr, entry) {
+                if (entry & IND_INDIRECTION) {
+                        /* Free the previous indirection page */
+                        if (ind & IND_INDIRECTION) {
+                                kimage_free_entry(ind);
+                        }
+                        /* Save this indirection page until we are
+                         * done with it.
+                         */
+                        ind = entry;
+                }
+                else if (entry & IND_SOURCE) {
+                        kimage_free_entry(entry);
+                }
+        }
+        /* Free the final indirection page */
+        if (ind & IND_INDIRECTION) {
+                kimage_free_entry(ind);
+        }
+
+        /* Handle any machine specific cleanup */
+        machine_kexec_cleanup(image);
+
+        /* Free the kexec control pages... */
+        kimage_free_page_list(&image->control_pages);
+        kfree(image);
+}
+
+static kimage_entry_t *kimage_dst_used(struct kimage *image, unsigned long page)
+{
+        kimage_entry_t *ptr, entry;
+        unsigned long destination = 0;
+
+        for_each_kimage_entry(image, ptr, entry) {
+                if (entry & IND_DESTINATION) {
+                        destination = entry & PAGE_MASK;
+                }
+                else if (entry & IND_SOURCE) {
+                        if (page == destination) {
+                                return ptr;
+                        }
+                        destination += PAGE_SIZE;
+                }
+        }
+        return 0;
+}
+
+static struct page *kimage_alloc_page(struct kimage *image, unsigned int gfp_mask, unsigned long destination)
+{
+        /*
+         * Here we implement safeguards to ensure that a source page
+         * is not copied to its destination page before the data on
+         * the destination page is no longer useful.
+         *
+         * To do this we maintain the invariant that a source page is
+         * either its own destination page, or it is not a
+         * destination page at all.
+         *
+         * That is slightly stronger than required, but the proof
+         * that no problems will not occur is trivial, and the
+         * implementation is simply to verify.
+         *
+         * When allocating all pages normally this algorithm will run
+         * in O(N) time, but in the worst case it will run in O(N^2)
+         * time.   If the runtime is a problem the data structures can
+         * be fixed.
+         */
+        struct page *page;
+        unsigned long addr;
+
+        /*
+         * Walk through the list of destination pages, and see if I
+         * have a match.
+         */
+        list_for_each_entry(page, &image->dest_pages, lru) {
+                addr = page_to_pfn(page) << PAGE_SHIFT;
+                if (addr == destination) {
+                        list_del(&page->lru);
+                        return page;
+                }
+        }
+        page = NULL;
+        while (1) {
+                kimage_entry_t *old;
+
+                /* Allocate a page, if we run out of memory give up */
+                page = kimage_alloc_pages(gfp_mask, 0);
+                if (!page) {
+                        return 0;
+                }
+                /* If the page cannot be used file it away */
+                if (page_to_pfn(page) > (KEXEC_SOURCE_MEMORY_LIMIT >> PAGE_SHIFT)) {
+                        list_add(&page->lru, &image->unuseable_pages);
+                        continue;
+                }
+                addr = page_to_pfn(page) << PAGE_SHIFT;
+
+                /* If it is the destination page we want use it */
+                if (addr == destination)
+                        break;
+
+                /* If the page is not a destination page use it */
+                if (!kimage_is_destination_range(image, addr, addr + PAGE_SIZE))
+                        break;
+
+                /*
+                 * I know that the page is someones destination page.
+                 * See if there is already a source page for this
+                 * destination page.  And if so swap the source pages.
+                 */
+                old = kimage_dst_used(image, addr);
+                if (old) {
+                        /* If so move it */
+                        unsigned long old_addr;
+                        struct page *old_page;
+
+                        old_addr = *old & PAGE_MASK;
+                        old_page = pfn_to_page(old_addr >> PAGE_SHIFT);
+                        copy_highpage(page, old_page);
+                        *old = addr | (*old & ~PAGE_MASK);
+
+                        /* The old page I have found cannot be a
+                         * destination page, so return it.
+                         */
+                        addr = old_addr;
+                        page = old_page;
+                        break;
+                }
+                else {
+                        /* Place the page on the destination list I
+                         * will use it later.
+                         */
+                        list_add(&page->lru, &image->dest_pages);
+                }
+        }
+        return page;
+}
+
+static int kimage_load_normal_segment(struct kimage *image,
+        struct kexec_segment *segment)
+{
+        unsigned long maddr;
+        unsigned long ubytes, mbytes;
+        int result;
+        unsigned char *buf;
+
+        result = 0;
+        buf = segment->buf;
+        ubytes = segment->bufsz;
+        mbytes = segment->memsz;
+        maddr = segment->mem;
+
+        result = kimage_set_destination(image, maddr);
+        if (result < 0) {
+                goto out;
+        }
+        while(mbytes) {
+                struct page *page;
+                char *ptr;
+                size_t uchunk, mchunk;
+                page = kimage_alloc_page(image, GFP_HIGHUSER, maddr);
+                if (page == 0) {
+                        result  = -ENOMEM;
+                        goto out;
+                }
+                result = kimage_add_page(image, page_to_pfn(page) << PAGE_SHIFT);
+                if (result < 0) {
+                        goto out;
+                }
+                ptr = kmap(page);
+                /* Start with a clear page */
+                memset(ptr, 0, PAGE_SIZE);
+                ptr += maddr & ~PAGE_MASK;
+                mchunk = PAGE_SIZE - (maddr & ~PAGE_MASK);
+                if (mchunk > mbytes) {
+                        mchunk = mbytes;
+                }
+                uchunk = mchunk;
+                if (uchunk > ubytes) {
+                        uchunk = ubytes;
+                }
+                result = copy_from_user(ptr, buf, uchunk);
+                kunmap(page);
+                if (result) {
+                        result = (result < 0) ? result : -EIO;
+                        goto out;
+                }
+                ubytes -= uchunk;
+                maddr  += mchunk;
+                buf    += mchunk;
+                mbytes -= mchunk;
+        }
+ out:
+        return result;
+}
+
+static int kimage_load_crash_segment(struct kimage *image,
+        struct kexec_segment *segment)
+{
+        /* For crash dumps kernels we simply copy the data from
+         * user space to it's destination.
+         * We do things a page at a time for the sake of kmap.
+         */
+        unsigned long maddr;
+        unsigned long ubytes, mbytes;
+        int result;
+        unsigned char *buf;
+
+        result = 0;
+        buf = segment->buf;
+        ubytes = segment->bufsz;
+        mbytes = segment->memsz;
+        maddr = segment->mem;
+        while(mbytes) {
+                struct page *page;
+                char *ptr;
+                size_t uchunk, mchunk;
+                page = pfn_to_page(maddr >> PAGE_SHIFT);
+                if (page == 0) {
+                        result  = -ENOMEM;
+                        goto out;
+                }
+                ptr = kmap(page);
+                ptr += maddr & ~PAGE_MASK;
+                mchunk = PAGE_SIZE - (maddr & ~PAGE_MASK);
+                if (mchunk > mbytes) {
+                        mchunk = mbytes;
+                }
+                uchunk = mchunk;
+                if (uchunk > ubytes) {
+                        uchunk = ubytes;
+                        /* Zero the trailing part of the page */
+                        memset(ptr + uchunk, 0, mchunk - uchunk);
+                }
+                result = copy_from_user(ptr, buf, uchunk);
+                kunmap(page);
+                if (result) {
+                        result = (result < 0) ? result : -EIO;
+                        goto out;
+                }
+                ubytes -= uchunk;
+                maddr  += mchunk;
+                buf    += mchunk;
+                mbytes -= mchunk;
+        }
+ out:
+        return result;
+}
+
+static int kimage_load_segment(struct kimage *image,
+        struct kexec_segment *segment)
+{
+        int result = -ENOMEM;
+        switch(image->type) {
+        case KEXEC_TYPE_DEFAULT:
+                result = kimage_load_normal_segment(image, segment);
+                break;
+        case KEXEC_TYPE_CRASH:
+                result = kimage_load_crash_segment(image, segment);
+                break;
+        }
+        return result;
+}
+
+/*
+ * Exec Kernel system call: for obvious reasons only root may call it.
+ *
+ * This call breaks up into three pieces.
+ * - A generic part which loads the new kernel from the current
+ *   address space, and very carefully places the data in the
+ *   allocated pages.
+ *
+ * - A generic part that interacts with the kernel and tells all of
+ *   the devices to shut down.  Preventing on-going dmas, and placing
+ *   the devices in a consistent state so a later kernel can
+ *   reinitialize them.
+ *
+ * - A machine specific part that includes the syscall number
+ *   and the copies the image to it's final destination.  And
+ *   jumps into the image at entry.
+ *
+ * kexec does not sync, or unmount filesystems so if you need
+ * that to happen you need to do that yourself.
+ */
+struct kimage *kexec_image = NULL;
+static struct kimage *kexec_crash_image = NULL;
+/*
+ * A home grown binary mutex.
+ * Nothing can wait so this mutex is safe to use
+ * in interrupt context :)
+ */
+static int kexec_lock = 0;
+
+asmlinkage long sys_kexec_load(unsigned long entry,
+        unsigned long nr_segments, struct kexec_segment __user *segments,
+        unsigned long flags)
+{
+        struct kimage **dest_image, *image;
+        int locked;
+        int result;
+
+        /* We only trust the superuser with rebooting the system. */
+        if (!capable(CAP_SYS_BOOT))
+                return -EPERM;
+
+        /*
+         * Verify we have a legal set of flags
+         * This leaves us room for future extensions.
+         */
+        if ((flags & KEXEC_FLAGS) != (flags & ~KEXEC_ARCH_MASK))
+                return -EINVAL;
+
+        /* Verify we are on the appropriate architecture */
+        if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) &&
+                ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))
+        {
+                return -EINVAL;
+        }
+
+        /* Put an artificial cap on the number
+         * of segments passed to kexec_load.
+         */
+        if (nr_segments > KEXEC_SEGMENT_MAX)
+                return -EINVAL;
+
+        image = NULL;
+        result = 0;
+
+        /* Because we write directly to the reserved memory
+         * region when loading crash kernels we need a mutex here to
+         * prevent multiple crash  kernels from attempting to load
+         * simultaneously, and to prevent a crash kernel from loading
+         * over the top of a in use crash kernel.
+         *
+         * KISS: always take the mutex.
+         */
+        locked = xchg(&kexec_lock, 1);
+        if (locked) {
+                return -EBUSY;
+        }
+        dest_image = &kexec_image;
+        if (flags & KEXEC_ON_CRASH) {
+                dest_image = &kexec_crash_image;
+        }
+        if (nr_segments > 0) {
+                unsigned long i;
+                /* Loading another kernel to reboot into */
+                if ((flags & KEXEC_ON_CRASH) == 0) {
+                        result = kimage_normal_alloc(&image, entry, nr_segments, segments);
+                }
+                /* Loading another kernel to switch to if this one crashes */
+                else if (flags & KEXEC_ON_CRASH) {
+                        /* Free any current crash dump kernel before
+                         * we corrupt it.
+                         */
+                        kimage_free(xchg(&kexec_crash_image, NULL));
+                        result = kimage_crash_alloc(&image, entry, nr_segments, segments);
+                }
+                if (result) {
+                        goto out;
+                }
+                result = machine_kexec_prepare(image);
+                if (result) {
+                        goto out;
+                }
+                for(i = 0; i < nr_segments; i++) {
+                        result = kimage_load_segment(image, &image->segment[i]);
+                        if (result) {
+                                goto out;
+                        }
+                }
+                result = kimage_terminate(image);
+                if (result) {
+                        goto out;
+                }
+        }
+        /* Install the new kernel, and  Uninstall the old */
+        image = xchg(dest_image, image);
+
+ out:
+        xchg(&kexec_lock, 0); /* Release the mutex */
+        kimage_free(image);
+        return result;
+}
+
+#ifdef CONFIG_COMPAT
+asmlinkage long compat_sys_kexec_load(unsigned long entry,
+        unsigned long nr_segments, struct compat_kexec_segment __user *segments,
+        unsigned long flags)
+{
+        struct compat_kexec_segment in;
+        struct kexec_segment out, __user *ksegments;
+        unsigned long i, result;
+
+        /* Don't allow clients that don't understand the native
+         * architecture to do anything.
+         */
+        if ((flags & KEXEC_ARCH_MASK) == KEXEC_ARCH_DEFAULT) {
+                return -EINVAL;
+        }
+
+        if (nr_segments > KEXEC_SEGMENT_MAX) {
+                return -EINVAL;
+        }
+
+        ksegments = compat_alloc_user_space(nr_segments * sizeof(out));
+        for (i=0; i < nr_segments; i++) {
+                result = copy_from_user(&in, &segments[i], sizeof(in));
+                if (result) {
+                        return -EFAULT;
+                }
+
+                out.buf   = compat_ptr(in.buf);
+                out.bufsz = in.bufsz;
+                out.mem   = in.mem;
+                out.memsz = in.memsz;
+
+                result = copy_to_user(&ksegments[i], &out, sizeof(out));
+                if (result) {
+                        return -EFAULT;
+                }
+        }
+
+        return sys_kexec_load(entry, nr_segments, ksegments, flags);
+}
+#endif
+
+void crash_kexec(void)
+{
+        struct kimage *image;
+        int locked;
+
+
+        /* Take the kexec_lock here to prevent sys_kexec_load
+         * running on one cpu from replacing the crash kernel
+         * we are using after a panic on a different cpu.
+         *
+         * If the crash kernel was not located in a fixed area
+         * of memory the xchg(&kexec_crash_image) would be
+         * sufficient.  But since I reuse the memory...
+         */
+        locked = xchg(&kexec_lock, 1);
+        if (!locked) {
+                image = xchg(&kexec_crash_image, NULL);
+                if (image) {
+                        machine_crash_shutdown();
+                        machine_kexec(image);
+                }
+                xchg(&kexec_lock, 0);
+        }
+}
diff --git a/kernel/panic.c b/kernel/panic.c
index 081f7465fc8d..66f43d33cd80 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -18,6 +18,7 @@
 #include <linux/sysrq.h>
 #include <linux/interrupt.h>
 #include <linux/nmi.h>
+#include <linux/kexec.h>
 
 int panic_timeout;
 int panic_on_oops;
@@ -63,6 +64,13 @@ NORET_TYPE void panic(const char * fmt, ...)
         unsigned long caller = (unsigned long) __builtin_return_address(0);
 #endif
 
+        /*
+         * It's possible to come here directly from a panic-assertion and not
+         * have preempt disabled. Some functions called from here want
+         * preempt to be disabled. No point enabling it later though...
+         */
+        preempt_disable();
+
         bust_spinlocks(1);
         va_start(args, fmt);
         vsnprintf(buf, sizeof(buf), fmt, args);
@@ -70,7 +78,19 @@ NORET_TYPE void panic(const char * fmt, ...)
         printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);
         bust_spinlocks(0);
 
+        /*
+         * If we have crashed and we have a crash kernel loaded let it handle
+         * everything else.
+         * Do we want to call this before we try to display a message?
+         */
+        crash_kexec();
+
 #ifdef CONFIG_SMP
+        /*
+         * Note smp_send_stop is the usual smp shutdown function, which
+         * unfortunately means it may not be hardened to work in a panic
+         * situation.
+         */
         smp_send_stop();
 #endif
 
@@ -79,8 +99,7 @@ NORET_TYPE void panic(const char * fmt, ...)
         if (!panic_blink)
                 panic_blink = no_blink;
 
-        if (panic_timeout > 0)
-        {
+        if (panic_timeout > 0) {
                 /*
                  * Delay timeout seconds before rebooting the machine. 
                  * We can't use the "normal" timers since we just panicked..
diff --git a/kernel/sys.c b/kernel/sys.c
index dac10161ca23..9a24374c23bc 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -16,6 +16,8 @@
 #include <linux/init.h>
 #include <linux/highuid.h>
 #include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/kexec.h>
 #include <linux/workqueue.h>
 #include <linux/device.h>
 #include <linux/key.h>
@@ -439,6 +441,24 @@ asmlinkage long sys_reboot(int magic1, int magic2, unsigned int cmd, void __user
                 machine_restart(buffer);
                 break;
 
+#ifdef CONFIG_KEXEC
+        case LINUX_REBOOT_CMD_KEXEC:
+        {
+                struct kimage *image;
+                image = xchg(&kexec_image, 0);
+                if (!image) {
+                        unlock_kernel();
+                        return -EINVAL;
+                }
+                notifier_call_chain(&reboot_notifier_list, SYS_RESTART, NULL);
+                system_state = SYSTEM_RESTART;
+                device_shutdown();
+                printk(KERN_EMERG "Starting new kernel\n");
+                machine_shutdown();
+                machine_kexec(image);
+                break;
+        }
+#endif
 #ifdef CONFIG_SOFTWARE_SUSPEND
         case LINUX_REBOOT_CMD_SW_SUSPEND:
                 {
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 6f15bea7d1a8..29196ce9b40f 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -18,6 +18,8 @@ cond_syscall(sys_acct);
 cond_syscall(sys_lookup_dcookie);
 cond_syscall(sys_swapon);
 cond_syscall(sys_swapoff);
+cond_syscall(sys_kexec_load);
+cond_syscall(compat_sys_kexec_load);
 cond_syscall(sys_init_module);
 cond_syscall(sys_delete_module);
 cond_syscall(sys_socketpair);