KVM: x86: improve reexecute_instruction
The current reexecute_instruction can not well detect the failed instruction
emulation. It allows guest to retry all the instructions except it accesses
on error pfn
For example, some cases are nested-write-protect - if the page we want to
write is used as PDE but it chains to itself. Under this case, we should
stop the emulation and report the case to userspace
Reviewed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6f9cab0..e00dd05 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4751,7 +4751,8 @@
return r;
}
-static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2)
+static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2,
+ bool write_fault_to_shadow_pgtable)
{
gpa_t gpa = cr2;
pfn_t pfn;
@@ -4808,7 +4809,13 @@
* guest to let CPU execute the instruction.
*/
kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa));
- return true;
+
+ /*
+ * If the access faults on its page table, it can not
+ * be fixed by unprotecting shadow page and it should
+ * be reported to userspace.
+ */
+ return !write_fault_to_shadow_pgtable;
}
static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
@@ -4867,7 +4874,13 @@
int r;
struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
bool writeback = true;
+ bool write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable;
+ /*
+ * Clear write_fault_to_shadow_pgtable here to ensure it is
+ * never reused.
+ */
+ vcpu->arch.write_fault_to_shadow_pgtable = false;
kvm_clear_exception_queue(vcpu);
if (!(emulation_type & EMULTYPE_NO_DECODE)) {
@@ -4886,7 +4899,8 @@
if (r != EMULATION_OK) {
if (emulation_type & EMULTYPE_TRAP_UD)
return EMULATE_FAIL;
- if (reexecute_instruction(vcpu, cr2))
+ if (reexecute_instruction(vcpu, cr2,
+ write_fault_to_spt))
return EMULATE_DONE;
if (emulation_type & EMULTYPE_SKIP)
return EMULATE_FAIL;
@@ -4916,7 +4930,7 @@
return EMULATE_DONE;
if (r == EMULATION_FAILED) {
- if (reexecute_instruction(vcpu, cr2))
+ if (reexecute_instruction(vcpu, cr2, write_fault_to_spt))
return EMULATE_DONE;
return handle_emulation_failure(vcpu);