KVM: x86 emulator: restart string instruction without going back to a guest.

Currently when string instruction is only partially complete we go back
to a guest mode, guest tries to reexecute instruction and exits again
and at this point emulation continues. Avoid all of this by restarting
instruction without going back to a guest mode, but return to a guest
mode each 1024 iterations to allow interrupt injection. Pending
exception causes immediate guest entry too.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 658e8e8155cb..c88cb8145283 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3755,6 +3755,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 		return EMULATE_DONE;
 	}
 
+restart:
 	r = x86_emulate_insn(&vcpu->arch.emulate_ctxt, &emulate_ops);
 	shadow_mask = vcpu->arch.emulate_ctxt.interruptibility;
 
@@ -3777,7 +3778,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 
 	if (r) {
 		if (kvm_mmu_unprotect_page_virt(vcpu, cr2))
-			return EMULATE_DONE;
+			goto done;
 		if (!vcpu->mmio_needed) {
 			kvm_report_emulation_failure(vcpu, "mmio");
 			return EMULATE_FAIL;
@@ -3792,6 +3793,13 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 		return EMULATE_DO_MMIO;
 	}
 
+done:
+	if (vcpu->arch.exception.pending)
+		vcpu->arch.emulate_ctxt.restart = false;
+
+	if (vcpu->arch.emulate_ctxt.restart)
+		goto restart;
+
 	return EMULATE_DONE;
 }
 EXPORT_SYMBOL_GPL(emulate_instruction);
@@ -4560,6 +4568,15 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 			goto out;
 		}
 	}
+	if (vcpu->arch.emulate_ctxt.restart) {
+		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+		r = emulate_instruction(vcpu, 0, 0, EMULTYPE_NO_DECODE);
+		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+		if (r == EMULATE_DO_MMIO) {
+			r = 0;
+			goto out;
+		}
+	}
 	if (kvm_run->exit_reason == KVM_EXIT_HYPERCALL)
 		kvm_register_write(vcpu, VCPU_REGS_RAX,
 				     kvm_run->hypercall.ret);