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[Xen-devel] [PATCH v4.2 4/5] xen-gntdev: Support mapping in HVM domains

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] [PATCH v4.2 4/5] xen-gntdev: Support mapping in HVM domains
From: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
Date: Fri, 21 Jan 2011 09:38:09 -0500
Cc: jeremy@xxxxxxxx, Ian.Campbell@xxxxxxxxxx, konrad.wilk@xxxxxxxxxx
Delivery-date: Fri, 21 Jan 2011 06:38:54 -0800
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HVM does not allow direct PTE modification, so instead we request
that Xen change its internal p2m mappings on the allocated pages and
map the memory into userspace normally.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
 drivers/xen/gntdev.c      |  115 +++++++++++++++++++++++++++++++-------------
 drivers/xen/grant-table.c |    6 ++
 2 files changed, 87 insertions(+), 34 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 11876bb..c9d009c 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -32,6 +32,7 @@
 #include <linux/sched.h>
 #include <linux/spinlock.h>
 #include <linux/slab.h>
+#include <linux/highmem.h>
 
 #include <xen/xen.h>
 #include <xen/grant_table.h>
@@ -52,6 +53,8 @@ MODULE_PARM_DESC(limit, "Maximum number of grants that may be 
mapped by "
 
 static atomic_t pages_mapped = ATOMIC_INIT(0);
 
+static int use_ptemod = 0;
+
 struct gntdev_priv {
        struct list_head maps;
        /* lock protects maps from concurrent changes */
@@ -74,6 +77,8 @@ struct grant_map {
        struct page **pages;
 };
 
+static int unmap_grant_pages(struct grant_map *map, int offset, int pages);
+
 /* ------------------------------------------------------------------ */
 
 static void gntdev_print_maps(struct gntdev_priv *priv,
@@ -180,11 +185,32 @@ static void gntdev_put_map(struct grant_map *map)
        
        atomic_sub(map->count, &pages_mapped);
 
-       if (map->pages)
+       if (map->pages) {
+               if (!use_ptemod)
+                       unmap_grant_pages(map, 0, map->count);
+
                for (i = 0; i < map->count; i++) {
-                       if (map->pages[i])
+                       uint32_t check, *tmp;
+                       if (!map->pages[i])
+                               continue;
+                       /* XXX When unmapping in an HVM domain, Xen will
+                        * sometimes end up mapping the GFN to an invalid MFN.
+                        * In this case, writes will be discarded and reads will
+                        * return all 0xFF bytes.  Leak these unusable GFNs
+                        * until Xen supports fixing their p2m mapping.
+                        */
+                       tmp = kmap(map->pages[i]);
+                       *tmp = 0xdeaddead;
+                       mb();
+                       check = *tmp;
+                       kunmap(map->pages[i]);
+                       if (check == 0xdeaddead)
                                __free_page(map->pages[i]);
+                       else
+                               pr_debug("Discard page %d=%ld\n", i,
+                                       page_to_pfn(map->pages[i]));
                }
+       }
        kfree(map->pages);
        kfree(map->grants);
        kfree(map->map_ops);
@@ -199,17 +225,16 @@ static int find_grant_ptes(pte_t *pte, pgtable_t token,
 {
        struct grant_map *map = data;
        unsigned int pgnr = (addr - map->vma->vm_start) >> PAGE_SHIFT;
+       int flags = map->flags | GNTMAP_application_map | GNTMAP_contains_pte;
        u64 pte_maddr;
 
        BUG_ON(pgnr >= map->count);
        pte_maddr = arbitrary_virt_to_machine(pte).maddr;
 
-       gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr,
-                         GNTMAP_contains_pte | map->flags,
+       gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, flags,
                          map->grants[pgnr].ref,
                          map->grants[pgnr].domid);
-       gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr,
-                           GNTMAP_contains_pte | map->flags,
+       gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr, flags,
                            0 /* handle */);
        return 0;
 }
@@ -217,6 +242,19 @@ static int find_grant_ptes(pte_t *pte, pgtable_t token,
 static int map_grant_pages(struct grant_map *map)
 {
        int i, err = 0;
+       phys_addr_t addr;
+
+       if (!use_ptemod) {
+               for (i = 0; i < map->count; i++) {
+                       addr = (phys_addr_t)
+                               pfn_to_kaddr(page_to_pfn(map->pages[i]));
+                       gnttab_set_map_op(&map->map_ops[i], addr, map->flags,
+                               map->grants[i].ref,
+                               map->grants[i].domid);
+                       gnttab_set_unmap_op(&map->unmap_ops[i], addr,
+                               map->flags, 0 /* handle */);
+               }
+       }
 
        pr_debug("map %d+%d\n", map->index, map->count);
        err = gnttab_map_refs(map->map_ops, map->pages, map->count);
@@ -261,17 +299,8 @@ static void gntdev_vma_close(struct vm_area_struct *vma)
        gntdev_put_map(map);
 }
 
-static int gntdev_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
-{
-       pr_debug("vaddr %p, pgoff %ld (shouldn't happen)\n",
-                       vmf->virtual_address, vmf->pgoff);
-       vmf->flags = VM_FAULT_ERROR;
-       return 0;
-}
-
 static struct vm_operations_struct gntdev_vmops = {
        .close = gntdev_vma_close,
-       .fault = gntdev_vma_fault,
 };
 
 /* ------------------------------------------------------------------ */
@@ -356,14 +385,16 @@ static int gntdev_open(struct inode *inode, struct file 
*flip)
        INIT_LIST_HEAD(&priv->maps);
        spin_lock_init(&priv->lock);
 
-       priv->mm = get_task_mm(current);
-       if (!priv->mm) {
-               kfree(priv);
-               return -ENOMEM;
+       if (use_ptemod) {
+               priv->mm = get_task_mm(current);
+               if (!priv->mm) {
+                       kfree(priv);
+                       return -ENOMEM;
+               }
+               priv->mn.ops = &gntdev_mmu_ops;
+               ret = mmu_notifier_register(&priv->mn, priv->mm);
+               mmput(priv->mm);
        }
-       priv->mn.ops = &gntdev_mmu_ops;
-       ret = mmu_notifier_register(&priv->mn, priv->mm);
-       mmput(priv->mm);
 
        if (ret) {
                kfree(priv);
@@ -391,7 +422,8 @@ static int gntdev_release(struct inode *inode, struct file 
*flip)
        }
        spin_unlock(&priv->lock);
 
-       mmu_notifier_unregister(&priv->mn, priv->mm);
+       if (use_ptemod)
+               mmu_notifier_unregister(&priv->mn, priv->mm);
        kfree(priv);
        return 0;
 }
@@ -517,7 +549,7 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
        int index = vma->vm_pgoff;
        int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
        struct grant_map *map;
-       int err = -EINVAL;
+       int i, err = -EINVAL;
 
        if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
                return -EINVAL;
@@ -529,9 +561,9 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
        map = gntdev_find_map_index(priv, index, count);
        if (!map)
                goto unlock_out;
-       if (map->vma)
+       if (use_ptemod && map->vma)
                goto unlock_out;
-       if (priv->mm != vma->vm_mm) {
+       if (use_ptemod && priv->mm != vma->vm_mm) {
                printk(KERN_WARNING "Huh? Other mm?\n");
                goto unlock_out;
        }
@@ -543,20 +575,24 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
        vma->vm_flags |= VM_RESERVED|VM_DONTCOPY|VM_DONTEXPAND|VM_PFNMAP;
 
        vma->vm_private_data = map;
-       map->vma = vma;
 
-       map->flags = GNTMAP_host_map | GNTMAP_application_map;
+       if (use_ptemod)
+               map->vma = vma;
+
+       map->flags = GNTMAP_host_map;
        if (!(vma->vm_flags & VM_WRITE))
                map->flags |= GNTMAP_readonly;
 
        spin_unlock(&priv->lock);
 
-       err = apply_to_page_range(vma->vm_mm, vma->vm_start,
-                                 vma->vm_end - vma->vm_start,
-                                 find_grant_ptes, map);
-       if (err) {
-               printk(KERN_WARNING "find_grant_ptes() failure.\n");
-               return err;
+       if (use_ptemod) {
+               err = apply_to_page_range(vma->vm_mm, vma->vm_start,
+                                         vma->vm_end - vma->vm_start,
+                                         find_grant_ptes, map);
+               if (err) {
+                       printk(KERN_WARNING "find_grant_ptes() failure.\n");
+                       return err;
+               }
        }
 
        err = map_grant_pages(map);
@@ -567,6 +603,15 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
 
        map->is_mapped = 1;
 
+       if (!use_ptemod) {
+               for(i = 0; i < count; i++) {
+                       err = vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE,
+                                            map->pages[i]);
+                       if (err)
+                               return err;
+               }
+       }
+
        return 0;
 
 unlock_out:
@@ -596,6 +641,8 @@ static int __init gntdev_init(void)
 
        if (!xen_domain())
                return -ENODEV;
+       
+       use_ptemod = xen_pv_domain();
 
        err = misc_register(&gntdev_miscdev);
        if (err != 0) {
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 9ef54eb..9428ced 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -458,6 +458,9 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
        if (ret)
                return ret;
 
+       if (xen_feature(XENFEAT_auto_translated_physmap))
+               return ret;
+
        for (i = 0; i < count; i++) {
                /* m2p override only supported for GNTMAP_contains_pte mappings 
*/
                if (!(map_ops[i].flags & GNTMAP_contains_pte))
@@ -483,6 +486,9 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref 
*unmap_ops,
        if (ret)
                return ret;
 
+       if (xen_feature(XENFEAT_auto_translated_physmap))
+               return ret;
+
        for (i = 0; i < count; i++) {
                ret = m2p_remove_override(pages[i]);
                if (ret)
-- 
1.7.3.4


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