vmcore: introduce remap_oldmem_pfn_range()

For zfcpdump we can't map the HSA storage because it is only available via
a read interface.  Therefore, for the new vmcore mmap feature we have
introduce a new mechanism to create mappings on demand.

This patch introduces a new architecture function remap_oldmem_pfn_range()
that should be used to create mappings with remap_pfn_range() for oldmem
areas that can be directly mapped.  For zfcpdump this is everything
besides of the HSA memory.  For the areas that are not mapped by
remap_oldmem_pfn_range() a generic vmcore a new generic vmcore fault
handler mmap_vmcore_fault() is called.

This handler works as follows:

* Get already available or new page from page cache (find_or_create_page)
* Check if /proc/vmcore page is filled with data (PageUptodate)
* If yes:
  Return that page
* If no:
  Fill page using __vmcore_read(), set PageUptodate, and return page

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Jan Willeke <willeke@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 83 insertions, 8 deletions

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 02cb3ff108bc..d07b70a6eed5 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -21,6 +21,7 @@
 #include <linux/crash_dump.h>
 #include <linux/list.h>
 #include <linux/vmalloc.h>
+#include <linux/pagemap.h>
 #include <asm/uaccess.h>
 #include <asm/io.h>
 #include "internal.h"
@@ -153,11 +154,35 @@ ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos)
         return read_from_oldmem(buf, count, ppos, 0);
 }
 
+/*
+ * Architectures may override this function to map oldmem
+ */
+int __weak remap_oldmem_pfn_range(struct vm_area_struct *vma,
+                                  unsigned long from, unsigned long pfn,
+                                  unsigned long size, pgprot_t prot)
+{
+        return remap_pfn_range(vma, from, pfn, size, prot);
+}
+
+/*
+ * Copy to either kernel or user space
+ */
+static int copy_to(void *target, void *src, size_t size, int userbuf)
+{
+        if (userbuf) {
+                if (copy_to_user((char __user *) target, src, size))
+                        return -EFAULT;
+        } else {
+                memcpy(target, src, size);
+        }
+        return 0;
+}
+
 /* Read from the ELF header and then the crash dump. On error, negative value is
  * returned otherwise number of bytes read are returned.
  */
-static ssize_t read_vmcore(struct file *file, char __user *buffer,
-                                size_t buflen, loff_t *fpos)
+static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
+                             int userbuf)
 {
         ssize_t acc = 0, tmp;
         size_t tsz;
@@ -174,7 +199,7 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
         /* Read ELF core header */
         if (*fpos < elfcorebuf_sz) {
                 tsz = min(elfcorebuf_sz - (size_t)*fpos, buflen);
-                if (copy_to_user(buffer, elfcorebuf + *fpos, tsz))
+                if (copy_to(buffer, elfcorebuf + *fpos, tsz, userbuf))
                         return -EFAULT;
                 buflen -= tsz;
                 *fpos += tsz;
@@ -192,7 +217,7 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
 
                 tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, buflen);
                 kaddr = elfnotes_buf + *fpos - elfcorebuf_sz;
-                if (copy_to_user(buffer, kaddr, tsz))
+                if (copy_to(buffer, kaddr, tsz, userbuf))
                         return -EFAULT;
                 buflen -= tsz;
                 *fpos += tsz;
@@ -208,7 +233,7 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
                 if (*fpos < m->offset + m->size) {
                         tsz = min_t(size_t, m->offset + m->size - *fpos, buflen);
                         start = m->paddr + *fpos - m->offset;
-                        tmp = read_from_oldmem(buffer, tsz, &start, 1);
+                        tmp = read_from_oldmem(buffer, tsz, &start, userbuf);
                         if (tmp < 0)
                                 return tmp;
                         buflen -= tsz;
@@ -225,6 +250,55 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
         return acc;
 }
 
+static ssize_t read_vmcore(struct file *file, char __user *buffer,
+                           size_t buflen, loff_t *fpos)
+{
+        return __read_vmcore((__force char *) buffer, buflen, fpos, 1);
+}
+
+/*
+ * The vmcore fault handler uses the page cache and fills data using the
+ * standard __vmcore_read() function.
+ *
+ * On s390 the fault handler is used for memory regions that can't be mapped
+ * directly with remap_pfn_range().
+ */
+static int mmap_vmcore_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+#ifdef CONFIG_S390
+        struct address_space *mapping = vma->vm_file->f_mapping;
+        pgoff_t index = vmf->pgoff;
+        struct page *page;
+        loff_t offset;
+        char *buf;
+        int rc;
+
+        page = find_or_create_page(mapping, index, GFP_KERNEL);
+        if (!page)
+                return VM_FAULT_OOM;
+        if (!PageUptodate(page)) {
+                offset = (loff_t) index << PAGE_CACHE_SHIFT;
+                buf = __va((page_to_pfn(page) << PAGE_SHIFT));
+                rc = __read_vmcore(buf, PAGE_SIZE, &offset, 0);
+                if (rc < 0) {
+                        unlock_page(page);
+                        page_cache_release(page);
+                        return (rc == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS;
+                }
+                SetPageUptodate(page);
+        }
+        unlock_page(page);
+        vmf->page = page;
+        return 0;
+#else
+        return VM_FAULT_SIGBUS;
+#endif
+}
+
+static const struct vm_operations_struct vmcore_mmap_ops = {
+        .fault = mmap_vmcore_fault,
+};
+
 /**
  * alloc_elfnotes_buf - allocate buffer for ELF note segment in
  *                      vmalloc memory
@@ -271,6 +345,7 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
 
         vma->vm_flags &= ~(VM_MAYWRITE | VM_MAYEXEC);
         vma->vm_flags |= VM_MIXEDMAP;
+        vma->vm_ops = &vmcore_mmap_ops;
 
         len = 0;
 
@@ -312,9 +387,9 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
 
                         tsz = min_t(size_t, m->offset + m->size - start, size);
                         paddr = m->paddr + start - m->offset;
-                        if (remap_pfn_range(vma, vma->vm_start + len,
-                                            paddr >> PAGE_SHIFT, tsz,
-                                            vma->vm_page_prot))
+                        if (remap_oldmem_pfn_range(vma, vma->vm_start + len,
+                                                   paddr >> PAGE_SHIFT, tsz,
+                                                   vma->vm_page_prot))
                                 goto fail;
                         size -= tsz;
                         start += tsz;