From aab61cc0d28f6fab0c2c9137d95dea54c7dbcf46 Mon Sep 17 00:00:00 2001 From: Anthony Liguori Date: Mon, 29 Oct 2007 15:15:20 -0500 Subject: [PATCH] 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 Signed-off-by: Avi Kivity --- drivers/kvm/kvm_main.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c index ac5ed00e90..f439e45233 100644 --- a/drivers/kvm/kvm_main.c +++ b/drivers/kvm/kvm_main.c @@ -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(¤t->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(¤t->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(¤t->mm->mmap_sem); + page = __gfn_to_page(kvm, gfn); + up_read(¤t->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; -- 2.39.5