From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755709AbaC0Laz (ORCPT ); Thu, 27 Mar 2014 07:30:55 -0400 Received: from mail-ee0-f44.google.com ([74.125.83.44]:42274 "EHLO mail-ee0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754951AbaC0Lat (ORCPT ); Thu, 27 Mar 2014 07:30:49 -0400 From: Paolo Bonzini To: linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org Subject: [RFC PATCH 2/5] KVM: x86: avoid useless set of KVM_REQ_EVENT after emulation Date: Thu, 27 Mar 2014 12:30:35 +0100 Message-Id: <1395919838-18466-3-git-send-email-pbonzini@redhat.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1395919838-18466-1-git-send-email-pbonzini@redhat.com> References: <1395919838-18466-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Despite the provisions to emulate up to 130 consecutive instructions, in practice KVM will emulate just one before exiting handle_invalid_guest_state, because x86_emulate_instructionn always sets KVM_REQ_EVENT. However, we only need to do this if an interrupt could be injected, which happens a) if an interrupt shadow bit (STI or MOV SS) has gone away; b) if the interrupt flag has just been set (because other instructions than STI can set it without enabling an interrupt shadow). This cuts another 250-300 clock cycles from the cost of emulating an instruction (530-870 cycles before the patch on kvm-unit-tests, 290-600 afterwards). Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 28 ++++++++++++++++++---------- 1 file changed, 18 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index fd31aada351b..ce9523345f2e 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -87,6 +87,7 @@ static u64 __read_mostly efer_reserved_bits = ~((u64)EFER_SCE); static void update_cr8_intercept(struct kvm_vcpu *vcpu); static void process_nmi(struct kvm_vcpu *vcpu); +static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags); struct kvm_x86_ops *kvm_x86_ops; EXPORT_SYMBOL_GPL(kvm_x86_ops); @@ -4856,8 +4857,10 @@ static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask) * means that the last instruction is an sti. We should not * leave the flag on in this case. The same goes for mov ss */ - if (!(int_shadow & mask)) + if (unlikely(int_shadow) && !(int_shadow & mask)) { kvm_x86_ops->set_interrupt_shadow(vcpu, mask); + kvm_make_request(KVM_REQ_EVENT, vcpu); + } } static void inject_emulated_exception(struct kvm_vcpu *vcpu) @@ -5083,20 +5086,18 @@ static int kvm_vcpu_check_hw_bp(unsigned long addr, u32 type, u32 dr7, return dr6; } -static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, int *r) +static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, unsigned long rflags, int *r) { struct kvm_run *kvm_run = vcpu->run; /* - * Use the "raw" value to see if TF was passed to the processor. - * Note that the new value of the flags has not been saved yet. + * rflags is the old, "raw" value of the flags. The new value has + * not been saved yet. * * This is correct even for TF set by the guest, because "the * processor will not generate this exception after the instruction * that sets the TF flag". */ - unsigned long rflags = kvm_x86_ops->get_rflags(vcpu); - if (unlikely(rflags & X86_EFLAGS_TF)) { if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { kvm_run->debug.arch.dr6 = DR6_BS | DR6_FIXED_1; @@ -5263,13 +5264,15 @@ restart: r = EMULATE_DONE; if (writeback) { + unsigned long rflags = kvm_x86_ops->get_rflags(vcpu); toggle_interruptibility(vcpu, ctxt->interruptibility); - kvm_make_request(KVM_REQ_EVENT, vcpu); vcpu->arch.emulate_regs_need_sync_to_vcpu = false; kvm_rip_write(vcpu, ctxt->eip); if (r == EMULATE_DONE) - kvm_vcpu_check_singlestep(vcpu, &r); - kvm_set_rflags(vcpu, ctxt->eflags); + kvm_vcpu_check_singlestep(vcpu, rflags, &r); + __kvm_set_rflags(vcpu, ctxt->eflags); + if (unlikely((ctxt->eflags & ~rflags) & X86_EFLAGS_IF)) + kvm_make_request(KVM_REQ_EVENT, vcpu); } else vcpu->arch.emulate_regs_need_sync_to_vcpu = true; @@ -7385,12 +7388,17 @@ unsigned long kvm_get_rflags(struct kvm_vcpu *vcpu) } EXPORT_SYMBOL_GPL(kvm_get_rflags); -void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) +static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) { if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP && kvm_is_linear_rip(vcpu, vcpu->arch.singlestep_rip)) rflags |= X86_EFLAGS_TF; kvm_x86_ops->set_rflags(vcpu, rflags); +} + +void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) +{ + __kvm_set_rflags(vcpu, rflags); kvm_make_request(KVM_REQ_EVENT, vcpu); } EXPORT_SYMBOL_GPL(kvm_set_rflags); -- 1.8.3.1