From 98eb2f8b145cee711984d42eff5d6f19b6b1df69 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 27 Mar 2014 09:51:52 +0100 Subject: [PATCH] KVM: vmx: speed up emulation of invalid guest state 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 --- arch/x86/kvm/vmx.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 8748c2e..5c7bbde 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -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; } -- 2.7.4