From: Sean Christopherson <seanjc@google.com>
To: Like Xu <like.xu.linux@gmail.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v2 06/21] KVM: x86/pmu: WARN and bug the VM if PMU is refreshed after vCPU has run
Date: Wed, 15 Feb 2023 07:20:56 -0800 [thread overview]
Message-ID: <Y+z4WF03dD/ytPl9@google.com> (raw)
In-Reply-To: <54d64f0e-871f-3004-d8a6-55c60affede0@gmail.com>
On Wed, Feb 15, 2023, Like Xu wrote:
> On 10/2/2023 8:31 am, Sean Christopherson wrote:
> > Now that KVM disallows changing feature MSRs, i.e. PERF_CAPABILITIES,
> > after running a vCPU, WARN and bug the VM if the PMU is refreshed after
> > the vCPU has run.
> >
> > Note, KVM has disallowed CPUID updates after running a vCPU since commit
> > feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN"), i.e.
> > PERF_CAPABILITIES was the only remaining way to trigger a PMU refresh
> > after KVM_RUN.
>
> A malicious user space could have saved the vcpu state and then deleted
> and recreated a new vcpu w/ previous state so that it would have a chance
> to re-set the features msr.
I don't follow. vcpu->arch.perf_capabilities and kvm_vcpu_has_run() are per-vCPU,
creating another vCPU will not let userspace trigger this WARN.
> The key to this issue may be focused on the KVM_CREATE_VM interface.
>
> How about the contract that when the first vcpu is created and "after
> KVM_RUN of any vcpu", the values of all feature msrs for all vcpus on
> the same guest cannot be changed, even if the (likely) first ever ran
> vcpu is deleted ?
I don't think that's necessary, as above the "freeze" happens per-vCPU.
next prev parent reply other threads:[~2023-02-15 15:21 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-10 0:31 [PATCH v2 00/21] KVM: x86: Disallow writes to feature MSRs post-KVM_RUN Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 01/21] KVM: x86: Rename kvm_init_msr_list() to clarify it inits multiple lists Sean Christopherson
2023-02-14 6:34 ` Xiaoyao Li
2023-02-10 0:31 ` [PATCH v2 02/21] KVM: x86: Add a helper to query whether or not a vCPU has ever run Sean Christopherson
2023-02-14 6:35 ` Xiaoyao Li
2023-02-10 0:31 ` [PATCH v2 03/21] KVM: x86: Add macros to track first...last VMX feature MSRs Sean Christopherson
2023-02-14 10:48 ` Like Xu
2023-02-14 18:51 ` Sean Christopherson
2023-02-15 3:20 ` Xiaoyao Li
2023-02-10 0:31 ` [PATCH v2 04/21] KVM: x86: Generate set of VMX feature MSRs using first/last definitions Sean Christopherson
2023-02-14 6:36 ` Xiaoyao Li
2023-02-10 0:31 ` [PATCH v2 05/21] KVM: x86: Disallow writes to immutable feature MSRs after KVM_RUN Sean Christopherson
2023-02-10 13:01 ` Yu Zhang
2023-02-10 16:31 ` Sean Christopherson
2023-02-14 6:39 ` Xiaoyao Li
2023-02-14 11:39 ` Like Xu
2023-02-15 22:36 ` Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 06/21] KVM: x86/pmu: WARN and bug the VM if PMU is refreshed after vCPU has run Sean Christopherson
2023-02-15 11:53 ` Like Xu
2023-02-15 15:20 ` Sean Christopherson [this message]
2023-02-10 0:31 ` [PATCH v2 07/21] KVM: x86/pmu: Zero out LBR capabilities during PMU refresh Sean Christopherson
2023-02-15 12:00 ` Like Xu
2023-02-15 15:17 ` Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 08/21] KVM: selftests: Split PMU caps sub-tests to avoid writing MSR after KVM_RUN Sean Christopherson
2023-02-14 7:27 ` Like Xu
2023-02-14 17:42 ` Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 09/21] KVM: selftests: Move 0/initial value PERF_CAPS checks to dedicated sub-test Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 10/21] KVM: selftests: Assert that full-width PMC writes are supported if PDCM=1 Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 11/21] KVM: selftests: Print out failing MSR and value in vcpu_set_msr() Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 12/21] KVM: selftests: Verify KVM preserves userspace writes to "durable" MSRs Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 13/21] KVM: selftests: Drop now-redundant checks on PERF_CAPABILITIES writes Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 14/21] KVM: selftests: Test all fungible features in PERF_CAPABILITIES Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 15/21] KVM: selftests: Test all immutable non-format bits " Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 16/21] KVM: selftests: Expand negative testing of guest writes to PERF_CAPABILITIES Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 17/21] KVM: selftests: Test post-KVM_RUN " Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 18/21] KVM: selftests: Drop "all done!" printf() from PERF_CAPABILITIES test Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 19/21] KVM: selftests: Refactor LBR_FMT test to avoid use of separate macro Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 20/21] KVM: selftests: Add negative testcase for PEBS format in PERF_CAPABILITIES Sean Christopherson
2023-02-10 0:31 ` [PATCH v2 21/21] KVM: selftests: Verify LBRs are disabled if vPMU is disabled Sean Christopherson
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