From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: RFC: VMX: initialize TSC offset relative to vm creation time Date: Wed, 10 Sep 2008 17:58:42 -0300 Message-ID: <20080910205842.GA12514@dmt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "David S. Ahern" , Chris Wright , Glauber de Oliveira Costa To: kvm-devel Return-path: Received: from mx1.redhat.com ([66.187.233.31]:50497 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751521AbYIJU7r (ORCPT ); Wed, 10 Sep 2008 16:59:47 -0400 Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: VMX initializes the TSC offset for each vcpu at different times, and also reinitializes it for vcpus other than 0 on APIC SIPI message. This bug causes the TSC's to appear unsynchronized in the guest, even if the host is good. Older Linux kernels don't handle the situation very well, so gettimeofday is likely to go backwards in time: http://www.mail-archive.com/kvm@vger.kernel.org/msg02955.html http://sourceforge.net/tracker/index.php?func=detail&aid=2025534&group_id=180599&atid=893831 Fix it by initializating the offset of each vcpu relative to vm creation time, and moving it from vmx_vcpu_reset to vmx_vcpu_setup, out of the APIC MP init path. Signed-off-by: Marcelo Tosatti Index: kvm.tip/arch/x86/kvm/vmx.c =================================================================== --- kvm.tip.orig/arch/x86/kvm/vmx.c +++ kvm.tip/arch/x86/kvm/vmx.c @@ -850,11 +850,8 @@ 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); } @@ -918,6 +915,7 @@ static int vmx_set_msr(struct kvm_vcpu * { struct vcpu_vmx *vmx = to_vmx(vcpu); struct kvm_msr_entry *msr; + u64 host_tsc; int ret = 0; switch (msr_index) { @@ -943,7 +941,8 @@ static int vmx_set_msr(struct kvm_vcpu * 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: @@ -2202,6 +2201,7 @@ static int vmx_vcpu_setup(struct vcpu_vm vmcs_writel(CR0_GUEST_HOST_MASK, ~0UL); vmcs_writel(CR4_GUEST_HOST_MASK, KVM_GUEST_CR4_MASK); + guest_write_tsc(0, vmx->vcpu.kvm->arch.vm_init_tsc); return 0; } @@ -2292,8 +2292,6 @@ static int vmx_vcpu_reset(struct kvm_vcp 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); Index: kvm.tip/arch/x86/kvm/x86.c =================================================================== --- kvm.tip.orig/arch/x86/kvm/x86.c +++ kvm.tip/arch/x86/kvm/x86.c @@ -4250,6 +4250,8 @@ struct kvm *kvm_arch_create_vm(void) INIT_LIST_HEAD(&kvm->arch.active_mmu_pages); INIT_LIST_HEAD(&kvm->arch.assigned_dev_head); + rdtscll(kvm->arch.vm_init_tsc); + return kvm; } Index: kvm.tip/include/asm-x86/kvm_host.h =================================================================== --- kvm.tip.orig/include/asm-x86/kvm_host.h +++ kvm.tip/include/asm-x86/kvm_host.h @@ -377,6 +377,7 @@ struct kvm_arch{ struct page *ept_identity_pagetable; bool ept_identity_pagetable_done; + u64 vm_init_tsc; }; struct kvm_vm_stat {