From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [patch 3/3] KVM: VMX: initialize TSC offset relative to vm creation time Date: Thu, 11 Dec 2008 20:45:05 +0100 Message-ID: <20081211194505.GA5468@dmt.cnet> References: <20081209011247.570596925@localhost.localdomain> <20081209012212.171143870@localhost.localdomain> <493F97B0.2060104@redhat.com> <20081210165307.GA28365@dmt.cnet> <49415010.3000108@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, Benjamin Serebrin To: Avi Kivity Return-path: Received: from mx2.redhat.com ([66.187.237.31]:42257 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757148AbYLKWrJ (ORCPT ); Thu, 11 Dec 2008 17:47:09 -0500 Content-Disposition: inline In-Reply-To: <49415010.3000108@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, Dec 11, 2008 at 07:38:24PM +0200, Avi Kivity wrote: > Marcelo Tosatti wrote: > > > >>> This looks fine, but have you tested it on a host with unsync tsc? >>> I'm worried that we'll get regressions there even on uniprocessor >>> guest. I'd like to keep the current behaviour for the special case >>> of >>> uniprocessor guest on unsync tsc host. >>> >> >> I don't see how. For UP guests the TSC is initialized to zero during >> vcpu setup, similarly to the current behaviour. >> >> Can you explain? >> >> > > On a host with an unsync tsc, when you move the vcpu to another cpu, the > tsc may jump backwards. Ok, this could cause the guest tsc to be initialized to a high value close to wraparound (in case the vcpu is migrated to a cpu with negative difference before vmx_vcpu_setup). What other regression could the updated patch introduce? diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 97215a4..5b70d83 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -378,6 +378,7 @@ struct kvm_arch{ unsigned long irq_sources_bitmap; unsigned long irq_states[KVM_IOAPIC_NUM_PINS]; + u64 vm_init_tsc; }; struct kvm_vm_stat { diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index e446f23..0879852 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -856,11 +856,8 @@ static u64 guest_read_tsc(void) * writes 'guest_tsc' into guest's timestamp counter "register" * guest_tsc = host_tsc + tsc_offset ==> tsc_offset = guest_tsc - host_tsc */ -static void guest_write_tsc(u64 guest_tsc) +static void guest_write_tsc(u64 guest_tsc, u64 host_tsc) { - u64 host_tsc; - - rdtscll(host_tsc); vmcs_write64(TSC_OFFSET, guest_tsc - host_tsc); } @@ -924,6 +921,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data) { struct vcpu_vmx *vmx = to_vmx(vcpu); struct kvm_msr_entry *msr; + u64 host_tsc; int ret = 0; switch (msr_index) { @@ -949,7 +947,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data) vmcs_writel(GUEST_SYSENTER_ESP, data); break; case MSR_IA32_TIME_STAMP_COUNTER: - guest_write_tsc(data); + rdtscll(host_tsc); + guest_write_tsc(data, host_tsc); break; case MSR_P6_PERFCTR0: case MSR_P6_PERFCTR1: @@ -2111,7 +2110,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx) { u32 host_sysenter_cs, msr_low, msr_high; u32 junk; - u64 host_pat; + u64 host_pat, tsc_this, tsc_base; unsigned long a; struct descriptor_table dt; int i; @@ -2239,6 +2238,12 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx) vmcs_writel(CR0_GUEST_HOST_MASK, ~0UL); vmcs_writel(CR4_GUEST_HOST_MASK, KVM_GUEST_CR4_MASK); + tsc_base = vmx->vcpu.kvm->arch.vm_init_tsc; + rdtscll(tsc_this); + if (tsc_this < vmx->vcpu.kvm->arch.vm_init_tsc) + tsc_base = tsc_this; + + guest_write_tsc(0, tsc_base); return 0; } @@ -2331,8 +2336,6 @@ static int vmx_vcpu_reset(struct kvm_vcpu *vcpu) vmcs_write32(GUEST_INTERRUPTIBILITY_INFO, 0); vmcs_write32(GUEST_PENDING_DBG_EXCEPTIONS, 0); - guest_write_tsc(0); - /* Special registers */ vmcs_write64(GUEST_IA32_DEBUGCTL, 0); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ba10287..b2d64eb 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4122,6 +4122,8 @@ struct kvm *kvm_arch_create_vm(void) /* Reserve bit 0 of irq_sources_bitmap for userspace irq source */ set_bit(KVM_USERSPACE_IRQ_SOURCE_ID, &kvm->arch.irq_sources_bitmap); + rdtscll(kvm->arch.vm_init_tsc); + return kvm; }