From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: [PATCH 32/41] KVM: SVM: Ensure timestamp counter monotonicity Date: Sun, 1 Apr 2007 17:35:29 +0300 Message-ID: <11754381393184-git-send-email-avi@qumranet.com> References: <1175438138288-git-send-email-avi@qumranet.com> <11754381381990-git-send-email-avi@qumranet.com> <11754381384009-git-send-email-avi@qumranet.com> <1175438138805-git-send-email-avi@qumranet.com> <11754381382515-git-send-email-avi@qumranet.com> <11754381383730-git-send-email-avi@qumranet.com> <11754381383144-git-send-email-avi@qumranet.com> <11754381381597-git-send-email-avi@qumranet.com> <1175438139242-git-send-email-avi@qumranet.com> <1175438139494-git-send-email-avi@qumranet.com> <11754381392046-git-send-email-avi@qumranet.com> <1175438139795-git-send-email-avi@qumranet.com> <1175438139430-git-send-email-avi@qumranet.com> <11754381393496-git-send-email-avi@qumranet.com> <11754381391514-git-send-email-avi@qumranet.com> <11754381392382-git-send-email-avi@qumranet.com> <11754381392358-git-send-email-avi@qumranet.com> <1175438139872-git-send-email-avi@qumranet.com> <11754381392921-git-send-email-avi@qumranet.com> <117543813978-git-send-email-avi@qumranet.com> <117543 81393061-git-send-email-avi@qumranet.com> <11754381392186-git-send-email-avi@qumranet.com> <117543813916-git-send-email-avi@qumranet.com> <1175438139530-git-send-email-avi@qumranet.com> <1175438139960-git-send-email-avi@qumranet.com> <1175438139816-git-send-email-avi@qumranet.com> <1175438139141-git-send-email-avi@qumranet.com> <11754381391993-git-send-email-avi@qumranet.com> <1175438139877-git-send-email-avi@qumranet.com> <11754381391119-git-send-email-avi@qumranet.com> <1175438139312-git-send-email-avi@qumranet.com> <11754381392527-git-send-email-avi@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Return-path: In-Reply-To: <11754381392527-git-send-email-avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org When a vcpu is migrated from one cpu to another, its timestamp counter may lose its monotonic property if the host has unsynced timestamp counters. This can confuse the guest, sometimes to the point of refusing to boot. As the rdtsc instruction is rather fast on AMD processors (7-10 cycles), we can simply record the last host tsc when we drop the cpu, and adjust the vcpu tsc offset when we detect that we've migrated to a different cpu. Signed-off-by: Avi Kivity --- drivers/kvm/kvm.h | 1 + drivers/kvm/svm.c | 21 +++++++++++++++++---- 2 files changed, 18 insertions(+), 4 deletions(-) diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h index f5e343c..6d0bd7a 100644 --- a/drivers/kvm/kvm.h +++ b/drivers/kvm/kvm.h @@ -244,6 +244,7 @@ struct kvm_vcpu { struct mutex mutex; int cpu; int launched; + u64 host_tsc; struct kvm_run *run; int interrupt_window_open; unsigned long irq_summary; /* bit vector: 1 per word in irq_pending */ diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c index 0542d33..ca2642f 100644 --- a/drivers/kvm/svm.c +++ b/drivers/kvm/svm.c @@ -459,7 +459,6 @@ static void init_vmcb(struct vmcb *vmcb) { struct vmcb_control_area *control = &vmcb->control; struct vmcb_save_area *save = &vmcb->save; - u64 tsc; control->intercept_cr_read = INTERCEPT_CR0_MASK | INTERCEPT_CR3_MASK | @@ -517,8 +516,7 @@ static void init_vmcb(struct vmcb *vmcb) control->iopm_base_pa = iopm_base; control->msrpm_base_pa = msrpm_base; - rdtscll(tsc); - control->tsc_offset = -tsc; + control->tsc_offset = 0; control->int_ctl = V_INTR_MASKING_MASK; init_seg(&save->es); @@ -606,11 +604,26 @@ static void svm_free_vcpu(struct kvm_vcpu *vcpu) static void svm_vcpu_load(struct kvm_vcpu *vcpu) { - get_cpu(); + int cpu; + + cpu = get_cpu(); + if (unlikely(cpu != vcpu->cpu)) { + u64 tsc_this, delta; + + /* + * Make sure that the guest sees a monotonically + * increasing TSC. + */ + rdtscll(tsc_this); + delta = vcpu->host_tsc - tsc_this; + vcpu->svm->vmcb->control.tsc_offset += delta; + vcpu->cpu = cpu; + } } static void svm_vcpu_put(struct kvm_vcpu *vcpu) { + rdtscll(vcpu->host_tsc); put_cpu(); } -- 1.5.0.5 ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV