From: Yang Weijiang <weijiang.yang@intel.com>
To: Jim Mattson <jmattson@google.com>
Cc: Yang Weijiang <weijiang.yang@intel.com>,
pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com,
wei.w.wang@intel.com, like.xu.linux@gmail.com,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 06/13] KVM: x86/vmx: Save/Restore host MSR_ARCH_LBR_CTL state
Date: Mon, 12 Jul 2021 17:50:34 +0800 [thread overview]
Message-ID: <20210712095034.GD12162@intel.com> (raw)
In-Reply-To: <CALMp9eQEs9pUyy1PpwLPG0_PtF07tR2Opw+1b=w4-knOwYPvvg@mail.gmail.com>
On Fri, Jul 09, 2021 at 03:54:53PM -0700, Jim Mattson wrote:
> On Fri, Jul 9, 2021 at 2:51 AM Yang Weijiang <weijiang.yang@intel.com> wrote:
> >
> > If host is using MSR_ARCH_LBR_CTL then save it before vm-entry
> > and reload it after vm-exit.
>
> I don't see anything being done here "before VM-entry" or "after
> VM-exit." This code seems to be invoked on vcpu_load and vcpu_put.
>
> In any case, I don't see why this one MSR is special. It seems that if
> the host is using the architectural LBR MSRs, then *all* of the host
> architectural LBR MSRs have to be saved on vcpu_load and restored on
> vcpu_put. Shouldn't kvm_load_guest_fpu() and kvm_put_guest_fpu() do
> that via the calls to kvm_save_current_fpu(vcpu->arch.user_fpu) and
> restore_fpregs_from_fpstate(&vcpu->arch.user_fpu->state)?
I looked back on the discussion thread:
https://patchwork.kernel.org/project/kvm/patch/20210303135756.1546253-8-like.xu@linux.intel.com/
not sure why this code is added, but IMO, although fpu save/restore in outer loop
covers this LBR MSR, but the operation points are far away from vm-entry/exit
point, i.e., the guest MSR setting could leak to host side for a signicant
long of time, it may cause host side profiling accuracy. if we save/restore it
manually, it'll mitigate the issue signifcantly.
next prev parent reply other threads:[~2021-07-12 9:39 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-09 10:04 [PATCH v5 00/13] Introduce Architectural LBR for vPMU Yang Weijiang
2021-07-09 10:04 ` [PATCH v5 01/13] perf/x86/intel: Fix the comment about guest LBR support on KVM Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 02/13] perf/x86/lbr: Simplify the exposure check for the LBR_INFO registers Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 03/13] KVM: x86: Add arch LBR MSRs to msrs_to_save_all list Yang Weijiang
2021-07-09 18:24 ` Jim Mattson
2021-07-12 8:55 ` Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 04/13] KVM: vmx/pmu: Emulate MSR_ARCH_LBR_DEPTH for guest Arch LBR Yang Weijiang
2021-07-09 20:35 ` Jim Mattson
2021-07-12 9:17 ` Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 05/13] KVM: vmx/pmu: Emulate MSR_ARCH_LBR_CTL " Yang Weijiang
2021-07-09 21:55 ` Jim Mattson
2021-07-12 9:36 ` Yang Weijiang
2021-07-12 10:10 ` Like Xu
2021-07-13 9:05 ` Yang Weijiang
2021-07-10 0:42 ` kernel test robot
2021-07-09 10:05 ` [PATCH v5 06/13] KVM: x86/vmx: Save/Restore host MSR_ARCH_LBR_CTL state Yang Weijiang
2021-07-09 22:54 ` Jim Mattson
2021-07-09 23:41 ` Jim Mattson
2021-07-12 9:53 ` Yang Weijiang
2021-07-12 10:19 ` Like Xu
2021-07-12 17:20 ` Jim Mattson
2021-07-12 17:45 ` Jim Mattson
2021-07-13 9:49 ` Like Xu
2021-07-13 17:00 ` Jim Mattson
2021-07-14 13:33 ` Like Xu
2021-07-14 16:15 ` Jim Mattson
2021-07-13 9:53 ` Yang Weijiang
2021-07-12 9:50 ` Yang Weijiang [this message]
2021-07-12 17:23 ` Jim Mattson
2021-07-13 9:47 ` Yang Weijiang
2021-07-13 10:16 ` Like Xu
2021-07-13 17:12 ` Jim Mattson
2021-07-14 13:55 ` Like Xu
2021-07-09 10:05 ` [PATCH v5 07/13] KVM: x86/pmu: Refactor code to support guest Arch LBR Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 08/13] KVM: x86: Refresh CPUID on writes to MSR_IA32_XSS Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 09/13] KVM: x86: Report XSS as an MSR to be saved if there are supported features Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 10/13] KVM: x86: Refine the matching and clearing logic for supported_xss Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 11/13] KVM: x86: Add XSAVE Support for Architectural LBR Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 12/13] KVM: x86/vmx: Check Arch LBR config when return perf capabilities Yang Weijiang
2021-07-09 10:05 ` [PATCH v5 13/13] KVM: x86/cpuid: Advise Arch LBR feature in CPUID Yang Weijiang
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