KVM: vmx: speed up emulation of invalid guest state (98eb2f8b) · Commits · 戴 / test

About 25% of the time spent in emulation of invalid guest state is wasted in checking whether emulation is required for the next instruction. However, this almost never changes except when a segment register (or TR or LDTR) changes, or when there is a mode transition (i.e. CR0 changes). In fact, vmx_set_segment and vmx_set_cr0 already modify vmx->emulation_required (except that the former for some reason uses |= instead of just an assignment). So there is no need to call guest_state_valid in the emulation loop. Emulation performance test results indicate 1650-2600 cycles for common instructions, versus 2300-3200 before this patch on a Sandy Bridge Xeon. Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -3672,7 +3672,7 @@ static void vmx_set_segment(struct kvm_vcpu *vcpu,
		vmcs_write32(sf->ar_bytes, vmx_segment_access_rights(var));

		out:
		vmx->emulation_required \|= emulation_required(vcpu);
		vmx->emulation_required = emulation_required(vcpu);
		}

		static void vmx_get_cs_db_l_bits(struct kvm_vcpu vcpu, int db, int *l)
		@@ -5640,7 +5640,7 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
		cpu_exec_ctrl = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
		intr_window_requested = cpu_exec_ctrl & CPU_BASED_VIRTUAL_INTR_PENDING;

		while (!guest_state_valid(vcpu) && count-- != 0) {
		while (vmx->emulation_required && count-- != 0) {
		if (intr_window_requested && vmx_interrupt_allowed(vcpu))
		return handle_interrupt_window(&vmx->vcpu);

		@@ -5674,7 +5674,6 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
		schedule();
		}

		vmx->emulation_required = emulation_required(vcpu);
		out:
		return ret;
		}

Admin message