KVM: x86: retry non-page-table writing instructions
If the emulation is caused by #PF and it is non-page_table writing instruction,
it means the VM-EXIT is caused by shadow page protected, we can zap the shadow
page and retry this instruction directly
The idea is from Avi
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e24edbc..7ba1ab7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4836,6 +4836,50 @@
return false;
}
+static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
+ unsigned long cr2, int emulation_type)
+{
+ struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
+ unsigned long last_retry_eip, last_retry_addr, gpa = cr2;
+
+ last_retry_eip = vcpu->arch.last_retry_eip;
+ last_retry_addr = vcpu->arch.last_retry_addr;
+
+ /*
+ * If the emulation is caused by #PF and it is non-page_table
+ * writing instruction, it means the VM-EXIT is caused by shadow
+ * page protected, we can zap the shadow page and retry this
+ * instruction directly.
+ *
+ * Note: if the guest uses a non-page-table modifying instruction
+ * on the PDE that points to the instruction, then we will unmap
+ * the instruction and go to an infinite loop. So, we cache the
+ * last retried eip and the last fault address, if we meet the eip
+ * and the address again, we can break out of the potential infinite
+ * loop.
+ */
+ vcpu->arch.last_retry_eip = vcpu->arch.last_retry_addr = 0;
+
+ if (!(emulation_type & EMULTYPE_RETRY))
+ return false;
+
+ if (x86_page_table_writing_insn(ctxt))
+ return false;
+
+ if (ctxt->eip == last_retry_eip && last_retry_addr == cr2)
+ return false;
+
+ vcpu->arch.last_retry_eip = ctxt->eip;
+ vcpu->arch.last_retry_addr = cr2;
+
+ if (!vcpu->arch.mmu.direct_map)
+ gpa = kvm_mmu_gva_to_gpa_write(vcpu, cr2, NULL);
+
+ kvm_mmu_unprotect_page(vcpu->kvm, gpa >> PAGE_SHIFT);
+
+ return true;
+}
+
int x86_emulate_instruction(struct kvm_vcpu *vcpu,
unsigned long cr2,
int emulation_type,
@@ -4877,6 +4921,9 @@
return EMULATE_DONE;
}
+ if (retry_instruction(ctxt, cr2, emulation_type))
+ return EMULATE_DONE;
+
/* this is needed for vmware backdoor interface to work since it
changes registers values during IO operation */
if (vcpu->arch.emulate_regs_need_sync_from_vcpu) {