KVM: x86 emulator: fix xchg instruction emulation

If the destination is a memory operand and the memory cannot
map to a valid page, the xchg instruction emulation and locked
instruction will not work on io regions and stuck in endless
loop. We should emulate exchange as write to fix it.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 689c2c3182ab..97aab036dabf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3562,6 +3562,10 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
                 goto emul_write;
 
         page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
+        if (is_error_page(page)) {
+                kvm_release_page_clean(page);
+                goto emul_write;
+        }
 
         kaddr = kmap_atomic(page, KM_USER0);
         kaddr += offset_in_page(gpa);