KVM: MMU: handle page removal with shadow mapping

Do not assume that a shadow mapping will always point to the same host
frame number.  Fixes crash with madvise(MADV_DONTNEED).

[avi: move after first printk(), add another printk()]

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index e49c4d433c0f..4ba85d95bd29 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -892,14 +892,25 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
                          int *ptwrite, gfn_t gfn, struct page *page)
 {
         u64 spte;
-        int was_rmapped = is_rmap_pte(*shadow_pte);
+        int was_rmapped = 0;
         int was_writeble = is_writeble_pte(*shadow_pte);
+        hfn_t host_pfn = (*shadow_pte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
 
         pgprintk("%s: spte %llx access %x write_fault %d"
                  " user_fault %d gfn %lx\n",
                  __FUNCTION__, *shadow_pte, pt_access,
                  write_fault, user_fault, gfn);
 
+        if (is_rmap_pte(*shadow_pte)) {
+                if (host_pfn != page_to_pfn(page)) {
+                        pgprintk("hfn old %lx new %lx\n",
+                                 host_pfn, page_to_pfn(page));
+                        rmap_remove(vcpu->kvm, shadow_pte);
+                }
+                else
+                        was_rmapped = 1;
+        }
+
         /*
          * We don't set the accessed bit, since we sometimes want to see
          * whether the guest actually used the pte (in order to detect