KVM: emulator: do not needlesly sync registers from emulator ctxt to vcpu

Commit Message

Gleb Natapov March 29, 2011, 12:08 p.m. UTC

None

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 35f81b1..3bf77c2 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -369,6 +369,8 @@  struct kvm_vcpu_arch {
 	/* emulate context */
 
 	struct x86_emulate_ctxt emulate_ctxt;
+	bool emulate_regs_need_sync_to_vcpu;
+	bool emulate_regs_need_sync_from_vcpu;
 
 	gpa_t time;
 	struct pvclock_vcpu_time_info hv_clock;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bfd7763..274c916 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4321,6 +4321,7 @@  static void init_emulate_ctxt(struct kvm_vcpu *vcpu)
 		? X86EMUL_MODE_PROT32 : X86EMUL_MODE_PROT16;
 	memset(c, 0, sizeof(struct decode_cache));
 	memcpy(c->regs, vcpu->arch.regs, sizeof c->regs);
+	vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
 }
 
 int kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq)
@@ -4403,6 +4404,7 @@  int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 {
 	int r;
 	struct decode_cache *c = &vcpu->arch.emulate_ctxt.decode;
+	bool writeback = true;
 
 	kvm_clear_exception_queue(vcpu);
 	vcpu->arch.mmio_fault_cr2 = cr2;
@@ -4443,9 +4445,12 @@  int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 		return EMULATE_DONE;
 	}
 
-	/* this is needed for vmware backdor interface to work since it
+	/* this is needed for vmware backdoor interface to work since it
 	   changes registers values  during IO operation */
-	memcpy(c->regs, vcpu->arch.regs, sizeof c->regs);
+	if (vcpu->arch.emulate_regs_need_sync_from_vcpu) {
+		vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
+		memcpy(c->regs, vcpu->arch.regs, sizeof c->regs);
+	}
 
 restart:
 	r = x86_emulate_insn(&vcpu->arch.emulate_ctxt);
@@ -4463,21 +4468,30 @@  restart:
 	} else if (vcpu->arch.pio.count) {
 		if (!vcpu->arch.pio.in)
 			vcpu->arch.pio.count = 0;
+		else
+			writeback = false;	
 		r = EMULATE_DO_MMIO;
 	} else if (vcpu->mmio_needed) {
 		if (vcpu->mmio_is_write)
 			vcpu->mmio_needed = 0;
+		else
+			writeback = false;	
 		r = EMULATE_DO_MMIO;
 	} else if (r == EMULATION_RESTART)
 		goto restart;
 	else
 		r = EMULATE_DONE;
 
-	toggle_interruptibility(vcpu, vcpu->arch.emulate_ctxt.interruptibility);
-	kvm_set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
-	kvm_make_request(KVM_REQ_EVENT, vcpu);
-	memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
-	kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
+	if (writeback) {
+		toggle_interruptibility(vcpu,
+				vcpu->arch.emulate_ctxt.interruptibility);
+		kvm_set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
+		memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
+		vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
+		kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
+	} else
+		vcpu->arch.emulate_regs_need_sync_to_vcpu = true;
 
 	return r;
 }
@@ -5437,6 +5451,18 @@  out:
 
 int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 {
+	if (vcpu->arch.emulate_regs_need_sync_to_vcpu) {
+		/*
+		 * We are here if userspace calls get_regs() in the middle of
+		 * instruction emulation. Registers state needs to be copied
+		 * back from emulation context to vcpu. Usrapace shouldn't do
+		 * that usually, but some bad designed PV devices (vmware
+		 * backdoor interface) need this to work
+		 */
+		struct decode_cache *c = &vcpu->arch.emulate_ctxt.decode;
+		memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
+		vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
+	}
 	regs->rax = kvm_register_read(vcpu, VCPU_REGS_RAX);
 	regs->rbx = kvm_register_read(vcpu, VCPU_REGS_RBX);
 	regs->rcx = kvm_register_read(vcpu, VCPU_REGS_RCX);
@@ -5464,6 +5490,9 @@  int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 
 int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 {
+	vcpu->arch.emulate_regs_need_sync_from_vcpu = true;
+	vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
+
 	kvm_register_write(vcpu, VCPU_REGS_RAX, regs->rax);
 	kvm_register_write(vcpu, VCPU_REGS_RBX, regs->rbx);
 	kvm_register_write(vcpu, VCPU_REGS_RCX, regs->rcx);