When not running in guest-debug mode (i.e. the guest controls the debug registers, having to take an exit for each DR access is a waste of time. If the guest gets into a state where each context switch causes DR to be saved and restored, this can take away as much as 40% of the execution time from the guest.
If the guest is running with vcpu->arch.db == vcpu->arch.eff_db, we can let it write freely to the debug registers and reload them on the next exit. We still need to exit on the first access, so that the KVM_DEBUGREG_WONT_EXIT flag is set in switch_db_regs; after that, further accesses to the debug registers will not cause a vmexit. Signed-off-by: Paolo Bonzini <[email protected]> --- arch/x86/kvm/svm.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 5ed67e9739f6..ac68edccc57c 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1683,6 +1683,21 @@ static void svm_set_dr6(struct kvm_vcpu *vcpu, unsigned long value) mark_dirty(svm->vmcb, VMCB_DR); } +static void svm_sync_dirty_debug_regs(struct kvm_vcpu *vcpu) +{ + struct vcpu_svm *svm = to_svm(vcpu); + + get_debugreg(vcpu->arch.db[0], 0); + get_debugreg(vcpu->arch.db[1], 1); + get_debugreg(vcpu->arch.db[2], 2); + get_debugreg(vcpu->arch.db[3], 3); + vcpu->arch.dr6 = svm_get_dr6(vcpu); + vcpu->arch.dr7 = svm->vmcb->save.dr7; + + vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_WONT_EXIT; + set_dr_intercepts(svm); +} + static void svm_set_dr7(struct kvm_vcpu *vcpu, unsigned long value) { struct vcpu_svm *svm = to_svm(vcpu); @@ -2974,6 +2989,17 @@ static int dr_interception(struct vcpu_svm *svm) unsigned long val; int err; + if (svm->vcpu.guest_debug == 0) { + /* + * No more DR vmexits; force a reload of the debug registers + * and reenter on this instruction. The next vmexit will + * retrieve the full state of the debug registers. + */ + clr_dr_intercepts(svm); + svm->vcpu.arch.switch_db_regs |= KVM_DEBUGREG_WONT_EXIT; + return 1; + } + if (!boot_cpu_has(X86_FEATURE_DECODEASSISTS)) return emulate_on_interception(svm); @@ -4302,6 +4328,7 @@ static struct kvm_x86_ops svm_x86_ops = { .get_dr6 = svm_get_dr6, .set_dr6 = svm_set_dr6, .set_dr7 = svm_set_dr7, + .sync_dirty_debug_regs = svm_sync_dirty_debug_regs, .cache_reg = svm_cache_reg, .get_rflags = svm_get_rflags, .set_rflags = svm_set_rflags, -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
