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xen-gntdev: Support mapping in HVM domains
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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.

Note:
The HVM path for map and unmap is slightly different: HVM keeps the pages
mapped until the area is deleted, while the PV case (use_ptemod being true)
must unmap them when userspace unmaps the range. In the normal use case,
this makes no difference to users since unmap time is deletion time.

[v2: Expanded commit descr.]
Signed-off-by: Daniel De Graaf <[email protected]>
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
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@dgdegraaf @konradwilk
dgdegraaf authored and konradwilk committed Feb 14, 2011
1 parent 68b025c commit aab8f11
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Showing 2 changed files with 89 additions and 34 deletions.
117 changes: 83 additions & 34 deletions drivers/xen/gntdev.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand All @@ -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;

struct gntdev_priv {
struct list_head maps;
/* lock protects maps from concurrent changes */
Expand All @@ -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,
Expand Down Expand Up @@ -179,11 +184,34 @@ 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.
*
* Confirmed present in Xen 4.1-RC3 with HVM source
*/
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);
Expand All @@ -198,24 +226,36 @@ 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;
}

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);
Expand Down Expand Up @@ -260,17 +300,8 @@ 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,
};

/* ------------------------------------------------------------------ */
Expand Down Expand Up @@ -355,14 +386,16 @@ 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);
Expand Down Expand Up @@ -390,7 +423,8 @@ 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;
}
Expand Down Expand Up @@ -515,7 +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;
Expand All @@ -527,9 +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;
}
Expand All @@ -541,20 +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);
Expand All @@ -565,6 +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:
Expand Down Expand Up @@ -595,6 +642,8 @@ static int __init gntdev_init(void)
if (!xen_domain())
return -ENODEV;

use_ptemod = xen_pv_domain();

err = misc_register(&gntdev_miscdev);
if (err != 0) {
printk(KERN_ERR "Could not register gntdev device\n");
Expand Down
6 changes: 6 additions & 0 deletions drivers/xen/grant-table.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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))
Expand All @@ -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)
Expand Down

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