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KVM: Fix gfn_to_page() acquiring mmap_sem twice 

KVM's nopage handler calls gfn_to_page() which acquires the mmap_sem when
calling out to get_user_pages().  nopage handlers are already invoked with the
mmap_sem held though.  Introduce a __gfn_to_page() for use by the nopage
handler which requires the lock to already be held.

This was noticed by tglx.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Anthony Liguori 2007-10-29 15:15:20 -05:00 committed by Avi Kivity
parent f78e0e2ee4
commit aab61cc0d2
1 changed files with 18 additions and 4 deletions
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22
drivers/kvm/kvm_main.c
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@ -633,7 +633,10 @@ int kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
}
EXPORT_SYMBOL_GPL(kvm_is_visible_gfn);
struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
/*
* Requires current->mm->mmap_sem to be held
*/
static struct page *__gfn_to_page(struct kvm *kvm, gfn_t gfn)
{
struct kvm_memory_slot *slot;
struct page *page[1];
@ -648,12 +651,10 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
return bad_page;
}
down_read(&current->mm->mmap_sem);
npages = get_user_pages(current, current->mm,
slot->userspace_addr
+ (gfn - slot->base_gfn) * PAGE_SIZE, 1,
1, 1, page, NULL);
up_read(&current->mm->mmap_sem);
if (npages != 1) {
get_page(bad_page);
return bad_page;
@ -661,6 +662,18 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
return page[0];
}
struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
{
struct page *page;
down_read(&current->mm->mmap_sem);
page = __gfn_to_page(kvm, gfn);
up_read(&current->mm->mmap_sem);
return page;
}
EXPORT_SYMBOL_GPL(gfn_to_page);
void kvm_release_page(struct page *page)
@ -2621,7 +2634,8 @@ static struct page *kvm_vm_nopage(struct vm_area_struct *vma,
pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
if (!kvm_is_visible_gfn(kvm, pgoff))
return NOPAGE_SIGBUS;
page = gfn_to_page(kvm, pgoff);
/* current->mm->mmap_sem is already held so call lockless version */
page = __gfn_to_page(kvm, pgoff);
if (is_error_page(page)) {
kvm_release_page(page);
return NOPAGE_SIGBUS;