xen: Add grant table support

Add Xen 'grant table' driver which allows granting of access to
selected local memory pages by other virtual machines and,
symmetrically, the mapping of remote memory pages which other virtual
machines have granted access to.

This driver is a prerequisite for many of the Xen virtual device
drivers, which grant the 'device driver domain' restricted and
temporary access to only those memory pages that are currently
involved in I/O operations.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

2 files changed, 583 insertions, 0 deletions

diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
new file mode 100644
index 000000000000..eb42b521eef9
--- /dev/null
+++ b/drivers/xen/Makefile
@@ -0,0 +1 @@
+obj-y   += grant-table.o
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
new file mode 100644
index 000000000000..ea94dbabf9a9
--- /dev/null
+++ b/drivers/xen/grant-table.c
@@ -0,0 +1,582 @@
+/******************************************************************************
+ * grant_table.c
+ *
+ * Granting foreign access to our memory reservation.
+ *
+ * Copyright (c) 2005-2006, Christopher Clark
+ * Copyright (c) 2004-2005, K A Fraser
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
+#include <linux/uaccess.h>
+
+#include <xen/interface/xen.h>
+#include <xen/page.h>
+#include <xen/grant_table.h>
+
+#include <asm/pgtable.h>
+#include <asm/sync_bitops.h>
+
+
+/* External tools reserve first few grant table entries. */
+#define NR_RESERVED_ENTRIES 8
+#define GNTTAB_LIST_END 0xffffffff
+#define GREFS_PER_GRANT_FRAME (PAGE_SIZE / sizeof(struct grant_entry))
+
+static grant_ref_t **gnttab_list;
+static unsigned int nr_grant_frames;
+static unsigned int boot_max_nr_grant_frames;
+static int gnttab_free_count;
+static grant_ref_t gnttab_free_head;
+static DEFINE_SPINLOCK(gnttab_list_lock);
+
+static struct grant_entry *shared;
+
+static struct gnttab_free_callback *gnttab_free_callback_list;
+
+static int gnttab_expand(unsigned int req_entries);
+
+#define RPP (PAGE_SIZE / sizeof(grant_ref_t))
+
+static inline grant_ref_t *__gnttab_entry(grant_ref_t entry)
+{
+        return &gnttab_list[(entry) / RPP][(entry) % RPP];
+}
+/* This can be used as an l-value */
+#define gnttab_entry(entry) (*__gnttab_entry(entry))
+
+static int get_free_entries(unsigned count)
+{
+        unsigned long flags;
+        int ref, rc;
+        grant_ref_t head;
+
+        spin_lock_irqsave(&gnttab_list_lock, flags);
+
+        if ((gnttab_free_count < count) &&
+            ((rc = gnttab_expand(count - gnttab_free_count)) < 0)) {
+                spin_unlock_irqrestore(&gnttab_list_lock, flags);
+                return rc;
+        }
+
+        ref = head = gnttab_free_head;
+        gnttab_free_count -= count;
+        while (count-- > 1)
+                head = gnttab_entry(head);
+        gnttab_free_head = gnttab_entry(head);
+        gnttab_entry(head) = GNTTAB_LIST_END;
+
+        spin_unlock_irqrestore(&gnttab_list_lock, flags);
+
+        return ref;
+}
+
+static void do_free_callbacks(void)
+{
+        struct gnttab_free_callback *callback, *next;
+
+        callback = gnttab_free_callback_list;
+        gnttab_free_callback_list = NULL;
+
+        while (callback != NULL) {
+                next = callback->next;
+                if (gnttab_free_count >= callback->count) {
+                        callback->next = NULL;
+                        callback->fn(callback->arg);
+                } else {
+                        callback->next = gnttab_free_callback_list;
+                        gnttab_free_callback_list = callback;
+                }
+                callback = next;
+        }
+}
+
+static inline void check_free_callbacks(void)
+{
+        if (unlikely(gnttab_free_callback_list))
+                do_free_callbacks();
+}
+
+static void put_free_entry(grant_ref_t ref)
+{
+        unsigned long flags;
+        spin_lock_irqsave(&gnttab_list_lock, flags);
+        gnttab_entry(ref) = gnttab_free_head;
+        gnttab_free_head = ref;
+        gnttab_free_count++;
+        check_free_callbacks();
+        spin_unlock_irqrestore(&gnttab_list_lock, flags);
+}
+
+static void update_grant_entry(grant_ref_t ref, domid_t domid,
+                               unsigned long frame, unsigned flags)
+{
+        /*
+         * Introducing a valid entry into the grant table:
+         *  1. Write ent->domid.
+         *  2. Write ent->frame:
+         *      GTF_permit_access:   Frame to which access is permitted.
+         *      GTF_accept_transfer: Pseudo-phys frame slot being filled by new
+         *                           frame, or zero if none.
+         *  3. Write memory barrier (WMB).
+         *  4. Write ent->flags, inc. valid type.
+         */
+        shared[ref].frame = frame;
+        shared[ref].domid = domid;
+        wmb();
+        shared[ref].flags = flags;
+}
+
+/*
+ * Public grant-issuing interface functions
+ */
+void gnttab_grant_foreign_access_ref(grant_ref_t ref, domid_t domid,
+                                     unsigned long frame, int readonly)
+{
+        update_grant_entry(ref, domid, frame,
+                           GTF_permit_access | (readonly ? GTF_readonly : 0));
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref);
+
+int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
+                                int readonly)
+{
+        int ref;
+
+        ref = get_free_entries(1);
+        if (unlikely(ref < 0))
+                return -ENOSPC;
+
+        gnttab_grant_foreign_access_ref(ref, domid, frame, readonly);
+
+        return ref;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access);
+
+int gnttab_query_foreign_access(grant_ref_t ref)
+{
+        u16 nflags;
+
+        nflags = shared[ref].flags;
+
+        return (nflags & (GTF_reading|GTF_writing));
+}
+EXPORT_SYMBOL_GPL(gnttab_query_foreign_access);
+
+int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
+{
+        u16 flags, nflags;
+
+        nflags = shared[ref].flags;
+        do {
+                flags = nflags;
+                if (flags & (GTF_reading|GTF_writing)) {
+                        printk(KERN_ALERT "WARNING: g.e. still in use!\n");
+                        return 0;
+                }
+        } while ((nflags = sync_cmpxchg(&shared[ref].flags, flags, 0)) != flags);
+
+        return 1;
+}
+EXPORT_SYMBOL_GPL(gnttab_end_foreign_access_ref);
+
+void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
+                               unsigned long page)
+{
+        if (gnttab_end_foreign_access_ref(ref, readonly)) {
+                put_free_entry(ref);
+                if (page != 0)
+                        free_page(page);
+        } else {
+                /* XXX This needs to be fixed so that the ref and page are
+                   placed on a list to be freed up later. */
+                printk(KERN_WARNING
+                       "WARNING: leaking g.e. and page still in use!\n");
+        }
+}
+EXPORT_SYMBOL_GPL(gnttab_end_foreign_access);
+
+int gnttab_grant_foreign_transfer(domid_t domid, unsigned long pfn)
+{
+        int ref;
+
+        ref = get_free_entries(1);
+        if (unlikely(ref < 0))
+                return -ENOSPC;
+        gnttab_grant_foreign_transfer_ref(ref, domid, pfn);
+
+        return ref;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer);
+
+void gnttab_grant_foreign_transfer_ref(grant_ref_t ref, domid_t domid,
+                                       unsigned long pfn)
+{
+        update_grant_entry(ref, domid, pfn, GTF_accept_transfer);
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer_ref);
+
+unsigned long gnttab_end_foreign_transfer_ref(grant_ref_t ref)
+{
+        unsigned long frame;
+        u16           flags;
+
+        /*
+         * If a transfer is not even yet started, try to reclaim the grant
+         * reference and return failure (== 0).
+         */
+        while (!((flags = shared[ref].flags) & GTF_transfer_committed)) {
+                if (sync_cmpxchg(&shared[ref].flags, flags, 0) == flags)
+                        return 0;
+                cpu_relax();
+        }
+
+        /* If a transfer is in progress then wait until it is completed. */
+        while (!(flags & GTF_transfer_completed)) {
+                flags = shared[ref].flags;
+                cpu_relax();
+        }
+
+        rmb();  /* Read the frame number /after/ reading completion status. */
+        frame = shared[ref].frame;
+        BUG_ON(frame == 0);
+
+        return frame;
+}
+EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer_ref);
+
+unsigned long gnttab_end_foreign_transfer(grant_ref_t ref)
+{
+        unsigned long frame = gnttab_end_foreign_transfer_ref(ref);
+        put_free_entry(ref);
+        return frame;
+}
+EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer);
+
+void gnttab_free_grant_reference(grant_ref_t ref)
+{
+        put_free_entry(ref);
+}
+EXPORT_SYMBOL_GPL(gnttab_free_grant_reference);
+
+void gnttab_free_grant_references(grant_ref_t head)
+{
+        grant_ref_t ref;
+        unsigned long flags;
+        int count = 1;
+        if (head == GNTTAB_LIST_END)
+                return;
+        spin_lock_irqsave(&gnttab_list_lock, flags);
+        ref = head;
+        while (gnttab_entry(ref) != GNTTAB_LIST_END) {
+                ref = gnttab_entry(ref);
+                count++;
+        }
+        gnttab_entry(ref) = gnttab_free_head;
+        gnttab_free_head = head;
+        gnttab_free_count += count;
+        check_free_callbacks();
+        spin_unlock_irqrestore(&gnttab_list_lock, flags);
+}
+EXPORT_SYMBOL_GPL(gnttab_free_grant_references);
+
+int gnttab_alloc_grant_references(u16 count, grant_ref_t *head)
+{
+        int h = get_free_entries(count);
+
+        if (h < 0)
+                return -ENOSPC;
+
+        *head = h;
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(gnttab_alloc_grant_references);
+
+int gnttab_empty_grant_references(const grant_ref_t *private_head)
+{
+        return (*private_head == GNTTAB_LIST_END);
+}
+EXPORT_SYMBOL_GPL(gnttab_empty_grant_references);
+
+int gnttab_claim_grant_reference(grant_ref_t *private_head)
+{
+        grant_ref_t g = *private_head;
+        if (unlikely(g == GNTTAB_LIST_END))
+                return -ENOSPC;
+        *private_head = gnttab_entry(g);
+        return g;
+}
+EXPORT_SYMBOL_GPL(gnttab_claim_grant_reference);
+
+void gnttab_release_grant_reference(grant_ref_t *private_head,
+                                    grant_ref_t release)
+{
+        gnttab_entry(release) = *private_head;
+        *private_head = release;
+}
+EXPORT_SYMBOL_GPL(gnttab_release_grant_reference);
+
+void gnttab_request_free_callback(struct gnttab_free_callback *callback,
+                                  void (*fn)(void *), void *arg, u16 count)
+{
+        unsigned long flags;
+        spin_lock_irqsave(&gnttab_list_lock, flags);
+        if (callback->next)
+                goto out;
+        callback->fn = fn;
+        callback->arg = arg;
+        callback->count = count;
+        callback->next = gnttab_free_callback_list;
+        gnttab_free_callback_list = callback;
+        check_free_callbacks();
+out:
+        spin_unlock_irqrestore(&gnttab_list_lock, flags);
+}
+EXPORT_SYMBOL_GPL(gnttab_request_free_callback);
+
+void gnttab_cancel_free_callback(struct gnttab_free_callback *callback)
+{
+        struct gnttab_free_callback **pcb;
+        unsigned long flags;
+
+        spin_lock_irqsave(&gnttab_list_lock, flags);
+        for (pcb = &gnttab_free_callback_list; *pcb; pcb = &(*pcb)->next) {
+                if (*pcb == callback) {
+                        *pcb = callback->next;
+                        break;
+                }
+        }
+        spin_unlock_irqrestore(&gnttab_list_lock, flags);
+}
+EXPORT_SYMBOL_GPL(gnttab_cancel_free_callback);
+
+static int grow_gnttab_list(unsigned int more_frames)
+{
+        unsigned int new_nr_grant_frames, extra_entries, i;
+
+        new_nr_grant_frames = nr_grant_frames + more_frames;
+        extra_entries       = more_frames * GREFS_PER_GRANT_FRAME;
+
+        for (i = nr_grant_frames; i < new_nr_grant_frames; i++) {
+                gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_ATOMIC);
+                if (!gnttab_list[i])
+                        goto grow_nomem;
+        }
+
+
+        for (i = GREFS_PER_GRANT_FRAME * nr_grant_frames;
+             i < GREFS_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)
+                gnttab_entry(i) = i + 1;
+
+        gnttab_entry(i) = gnttab_free_head;
+        gnttab_free_head = GREFS_PER_GRANT_FRAME * nr_grant_frames;
+        gnttab_free_count += extra_entries;
+
+        nr_grant_frames = new_nr_grant_frames;
+
+        check_free_callbacks();
+
+        return 0;
+
+grow_nomem:
+        for ( ; i >= nr_grant_frames; i--)
+                free_page((unsigned long) gnttab_list[i]);
+        return -ENOMEM;
+}
+
+static unsigned int __max_nr_grant_frames(void)
+{
+        struct gnttab_query_size query;
+        int rc;
+
+        query.dom = DOMID_SELF;
+
+        rc = HYPERVISOR_grant_table_op(GNTTABOP_query_size, &query, 1);
+        if ((rc < 0) || (query.status != GNTST_okay))
+                return 4; /* Legacy max supported number of frames */
+
+        return query.max_nr_frames;
+}
+
+static inline unsigned int max_nr_grant_frames(void)
+{
+        unsigned int xen_max = __max_nr_grant_frames();
+
+        if (xen_max > boot_max_nr_grant_frames)
+                return boot_max_nr_grant_frames;
+        return xen_max;
+}
+
+static int map_pte_fn(pte_t *pte, struct page *pmd_page,
+                      unsigned long addr, void *data)
+{
+        unsigned long **frames = (unsigned long **)data;
+
+        set_pte_at(&init_mm, addr, pte, mfn_pte((*frames)[0], PAGE_KERNEL));
+        (*frames)++;
+        return 0;
+}
+
+static int unmap_pte_fn(pte_t *pte, struct page *pmd_page,
+                        unsigned long addr, void *data)
+{
+
+        set_pte_at(&init_mm, addr, pte, __pte(0));
+        return 0;
+}
+
+static int gnttab_map(unsigned int start_idx, unsigned int end_idx)
+{
+        struct gnttab_setup_table setup;
+        unsigned long *frames;
+        unsigned int nr_gframes = end_idx + 1;
+        int rc;
+
+        frames = kmalloc(nr_gframes * sizeof(unsigned long), GFP_ATOMIC);
+        if (!frames)
+                return -ENOMEM;
+
+        setup.dom        = DOMID_SELF;
+        setup.nr_frames  = nr_gframes;
+        setup.frame_list = frames;
+
+        rc = HYPERVISOR_grant_table_op(GNTTABOP_setup_table, &setup, 1);
+        if (rc == -ENOSYS) {
+                kfree(frames);
+                return -ENOSYS;
+        }
+
+        BUG_ON(rc || setup.status);
+
+        if (shared == NULL) {
+                struct vm_struct *area;
+                area = alloc_vm_area(PAGE_SIZE * max_nr_grant_frames());
+                BUG_ON(area == NULL);
+                shared = area->addr;
+        }
+        rc = apply_to_page_range(&init_mm, (unsigned long)shared,
+                                 PAGE_SIZE * nr_gframes,
+                                 map_pte_fn, &frames);
+        BUG_ON(rc);
+        frames -= nr_gframes; /* adjust after map_pte_fn() */
+
+        kfree(frames);
+
+        return 0;
+}
+
+static int gnttab_resume(void)
+{
+        if (max_nr_grant_frames() < nr_grant_frames)
+                return -ENOSYS;
+        return gnttab_map(0, nr_grant_frames - 1);
+}
+
+static int gnttab_suspend(void)
+{
+        apply_to_page_range(&init_mm, (unsigned long)shared,
+                            PAGE_SIZE * nr_grant_frames,
+                            unmap_pte_fn, NULL);
+
+        return 0;
+}
+
+static int gnttab_expand(unsigned int req_entries)
+{
+        int rc;
+        unsigned int cur, extra;
+
+        cur = nr_grant_frames;
+        extra = ((req_entries + (GREFS_PER_GRANT_FRAME-1)) /
+                 GREFS_PER_GRANT_FRAME);
+        if (cur + extra > max_nr_grant_frames())
+                return -ENOSPC;
+
+        rc = gnttab_map(cur, cur + extra - 1);
+        if (rc == 0)
+                rc = grow_gnttab_list(extra);
+
+        return rc;
+}
+
+static int __devinit gnttab_init(void)
+{
+        int i;
+        unsigned int max_nr_glist_frames;
+        unsigned int nr_init_grefs;
+
+        if (!is_running_on_xen())
+                return -ENODEV;
+
+        nr_grant_frames = 1;
+        boot_max_nr_grant_frames = __max_nr_grant_frames();
+
+        /* Determine the maximum number of frames required for the
+         * grant reference free list on the current hypervisor.
+         */
+        max_nr_glist_frames = (boot_max_nr_grant_frames *
+                               GREFS_PER_GRANT_FRAME /
+                               (PAGE_SIZE / sizeof(grant_ref_t)));
+
+        gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),
+                              GFP_KERNEL);
+        if (gnttab_list == NULL)
+                return -ENOMEM;
+
+        for (i = 0; i < nr_grant_frames; i++) {
+                gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_KERNEL);
+                if (gnttab_list[i] == NULL)
+                        goto ini_nomem;
+        }
+
+        if (gnttab_resume() < 0)
+                return -ENODEV;
+
+        nr_init_grefs = nr_grant_frames * GREFS_PER_GRANT_FRAME;
+
+        for (i = NR_RESERVED_ENTRIES; i < nr_init_grefs - 1; i++)
+                gnttab_entry(i) = i + 1;
+
+        gnttab_entry(nr_init_grefs - 1) = GNTTAB_LIST_END;
+        gnttab_free_count = nr_init_grefs - NR_RESERVED_ENTRIES;
+        gnttab_free_head  = NR_RESERVED_ENTRIES;
+
+        printk("Grant table initialized\n");
+        return 0;
+
+ ini_nomem:
+        for (i--; i >= 0; i--)
+                free_page((unsigned long)gnttab_list[i]);
+        kfree(gnttab_list);
+        return -ENOMEM;
+}
+
+core_initcall(gnttab_init);