KVM: Fix a race condition for usage of is_hwpoison_address()

is_hwpoison_address accesses the page table, so the caller must hold
current->mm->mmap_sem in read mode. So fix its usage in hva_to_pfn of
kvm accordingly.

Comment is_hwpoison_address to remind other users.

Reported-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 5 insertions, 1 deletions

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 378b0f61fd3..6b44e52caca 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1298,6 +1298,9 @@ done:
         return ret;
 }
 
+/*
+ * The caller must hold current->mm->mmap_sem in read mode.
+ */
 int is_hwpoison_address(unsigned long addr)
 {
         pgd_t *pgdp;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 74f73192094..ec2e3c6ac7e 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -947,12 +947,13 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr)
         if (unlikely(npages != 1)) {
                 struct vm_area_struct *vma;
 
+                down_read(&current->mm->mmap_sem);
                 if (is_hwpoison_address(addr)) {
+                        up_read(&current->mm->mmap_sem);
                         get_page(hwpoison_page);
                         return page_to_pfn(hwpoison_page);
                 }
 
-                down_read(&current->mm->mmap_sem);
                 vma = find_vma(current->mm, addr);
 
                 if (vma == NULL || addr < vma->vm_start ||