From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752866AbeDLQfa (ORCPT ); Thu, 12 Apr 2018 12:35:30 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:38220 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752389AbeDLQf2 (ORCPT ); Thu, 12 Apr 2018 12:35:28 -0400 Subject: Re: [PATCH 1/2] X86/KVM: Properly restore 'tsc_offset' when running an L2 guest To: KarimAllah Ahmed , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Jim Mattson , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= References: <1523545958-28059-1-git-send-email-karahmed@amazon.de> From: Paolo Bonzini Openpgp: preference=signencrypt Autocrypt: addr=pbonzini@redhat.com; prefer-encrypt=mutual; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0f UGFvbG8gQm9uemluaSA8Ym9uemluaUBnbnUub3JnPsLBTQQTAQIAIwUCVEJ7AwIbAwcLCQgH AwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEH4VEAzNNmmxNcwOniaZVLsuy1lW/ntYCA0Caz0i sHpmecK8aWlvL9wpQCk4GlOX9L1emyYXZPmzIYB0IRqmSzAlZxi+A2qm9XOxs5gJ2xqMEXX5 FMtUH3kpkWWJeLqe7z0EoQdUI4EG988uv/tdZyqjUn2XJE+K01x7r3MkUSFz/HZKZiCvYuze VlS0NTYdUt5jBXualvAwNKfxEkrxeHjxgdFHjYWhjflahY7TNRmuqPM/Lx7wAuyoDjlYNE40 Z+Kun4/KjMbjgpcF4Nf3PJQR8qXI6p3so2qsSn91tY7DFSJO6v2HwFJkC2jU95wxfNmTEUZc znXahYbVOwCDJRuPrE5GKFd/XJU9u5hNtr/uYipHij01WXal2cce1S5mn1/HuM1yo1u8xdHy IupCd57EWI948e8BlhpujUCU2tzOb2iYS0kpmJ9/oLVZrOcSZCcCl2P0AaCAsj59z2kwQS9D du0WxUs8waso0Qq6tDEHo8yLCOJDzSz4oojTtWe4zsulVnWV+wu70AioemAT8S6JOtlu60C5 dHgQUD1Tp+ReXpDKXmjbASJx4otvW0qah3o6JaqO79tbDqIvncu3tewwp6c85uZd48JnIOh3 utBAu684nJakbbvZUGikJfxd887ATQRUQnHuAQgAx4dxXO6/Zun0eVYOnr5GRl76+2UrAAem Vv9Yfn2PbDIbxXqLff7oyVJIkw4WdhQIIvvtu5zH24iYjmdfbg8iWpP7NqxUQRUZJEWbx2CR wkMHtOmzQiQ2tSLjKh/cHeyFH68xjeLcinR7jXMrHQK+UCEw6jqi1oeZzGvfmxarUmS0uRuf fAb589AJW50kkQK9VD/9QC2FJISSUDnRC0PawGSZDXhmvITJMdD4TjYrePYhSY4uuIV02v02 8TVAaYbIhxvDY0hUQE4r8ZbGRLn52bEzaIPgl1p/adKfeOUeMReg/CkyzQpmyB1TSk8lDMxQ zCYHXAzwnGi8WU9iuE1P0wARAQABwsEzBBgBAgAJBQJUQnHuAhsMAAoJEH4VEAzNNmmxp1EO oJy0uZggJm7gZKeJ7iUpeX4eqUtqelUw6gU2daz2hE/jsxsTbC/w5piHmk1H1VWDKEM4bQBT uiJ0bfo55SWsUNN+c9hhIX+Y8LEe22izK3w7mRpvGcg+/ZRG4DEMHLP6JVsv5GMpoYwYOmHn plOzCXHvmdlW0i6SrMsBDl9rw4AtIa6bRwWLim1lQ6EM3PWifPrWSUPrPcw4OLSwFk0CPqC4 HYv/7ZnASVkR5EERFF3+6iaaVi5OgBd81F1TCvCX2BEyIDRZLJNvX3TOd5FEN+lIrl26xecz 876SvcOb5SL5SKg9/rCBufdPSjojkGFWGziHiFaYhbuI2E+NfWLJtd+ZvWAAV+O0d8vFFSvr iy9enJ8kxJwhC0ECbSKFY+W1eTIhMD3aeAKY90drozWEyHhENf4l/V+Ja5vOnW+gCDQkGt2Y 1lJAPPSIqZKvHzGShdh8DduC0U3xYkfbGAUvbxeepjgzp0uEnBXfPTy09JGpgWbg0w91GyfT /ujKaGd4vxG2Ei+MMNDmS1SMx7wu0evvQ5kT9NPzyq8R2GIhVSiAd2jioGuTjX6AZCFv3ToO 53DliFMkVTecLptsXaesuUHgL9dKIfvpm+rNXRn9wAwGjk0X/A== Message-ID: Date: Thu, 12 Apr 2018 18:35:25 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <1523545958-28059-1-git-send-email-karahmed@amazon.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/04/2018 17:12, KarimAllah Ahmed wrote: > When the TSC MSR is captured while an L2 guest is running then restored, > the 'tsc_offset' ends up capturing the L02 TSC_OFFSET instead of the L01 > TSC_OFFSET. So ensure that this is compensated for when storing the value. > > Cc: Jim Mattson > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: kvm@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: KarimAllah Ahmed > --- > arch/x86/kvm/vmx.c | 12 +++++++++--- > arch/x86/kvm/x86.c | 1 - > 2 files changed, 9 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index cff2f50..2f57571 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -2900,6 +2900,8 @@ static u64 guest_read_tsc(struct kvm_vcpu *vcpu) > */ > static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset) > { > + u64 l1_tsc_offset = 0; > + > if (is_guest_mode(vcpu)) { > /* > * We're here if L1 chose not to trap WRMSR to TSC. According > @@ -2908,16 +2910,20 @@ static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset) > * to the newly set TSC to get L2's TSC. > */ > struct vmcs12 *vmcs12; > + > /* recalculate vmcs02.TSC_OFFSET: */ > vmcs12 = get_vmcs12(vcpu); > - vmcs_write64(TSC_OFFSET, offset + > - (nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING) ? > - vmcs12->tsc_offset : 0)); > + > + l1_tsc_offset = nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING) ? > + vmcs12->tsc_offset : 0; > + vmcs_write64(TSC_OFFSET, offset + l1_tsc_offset); > } else { > trace_kvm_write_tsc_offset(vcpu->vcpu_id, > vmcs_read64(TSC_OFFSET), offset); > vmcs_write64(TSC_OFFSET, offset); > } > + > + vcpu->arch.tsc_offset = offset - l1_tsc_offset; Using both "offset + l1_tsc_offset" and "offset - l1_tsc_offset" in this function seems wrong to me: if vcpu->arch.tsc_offset must be "offset - l1_tsc_offset", then "offset" must be written to TSC_OFFSET. I think the bug was introduced by commit 3e3f50262. Before, vmx_read_tsc_offset returned the L02 offset; now it always contains the L01 offset. So the right fix is to adjust vcpu->arch.tsc_offset on nested vmentry/vmexit. If is_guest_mode(vcpu), kvm_read_l1_tsc must use a new kvm_x86_ops callback to subtract the L12 offset from the value it returns. Thanks, Paolo > } > > /* > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index ac42c85..1a2ed92 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1539,7 +1539,6 @@ EXPORT_SYMBOL_GPL(kvm_read_l1_tsc); > static void kvm_vcpu_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset) > { > kvm_x86_ops->write_tsc_offset(vcpu, offset); > - vcpu->arch.tsc_offset = offset; > } > > static inline bool kvm_check_tsc_unstable(void) >