Messages in this thread | | | Date | Wed, 23 Aug 2023 13:35:04 -0700 | Subject | Re: [PATCH] KVM: x86: Allow exposure of VMware backdoor Pseudo-PMCs when !enable_pmu | From | Sean Christopherson <> |
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On Tue, Aug 22, 2023, Like Xu wrote: > From: Like Xu <likexu@tencent.com> > > Fix kvm_pmu_rdpmc() logic to allow exposure of VMware backdoor Pseudo-PMCs > if pmu is globally disabled. > > In this usage scenario, once vmware_backdoor is enabled, the VMs can fully > utilize all of the vmware_backdoor-related resources, not just part of it, > i.e., vcpu should always be able to access the VMware backdoor Pseudo-PMCs > via RDPMC. Since the enable_pmu is more concerned with the visibility of > hardware pmu resources on the host, fix it to decouple the two knobs. > > The test case vmware_backdoors from KUT is used for validation.
Is there a real world need for this? Per commit 672ff6cff80c ("KVM: x86: Raise #GP when guest vCPU do not support PMU"), KVM's behavior is intentional. If there is a real world need, then (a) that justification needs to be provided, (b) this needs a Fixes:, and (c) this probably needs to be tagged for stable.
> Cc: Arbel Moshe <arbel.moshe@oracle.com> > Cc: Liran Alon <liran.alon@oracle.com> > Cc: Nikita Leshenko <nikita.leshchenko@oracle.com>
The expectation is that a Cc: in the changelog means the patch email is Cc'd to that person, i.e. one of the purposes of Cc: here is to record that people who might care about the patch have been made aware of its existence. stable@ is pretty much the only exception to that rule, as "Cc: stable@vger.kernel.org" is really just a metadata tag for scripts.
FWIW, I believe Liran no longer works for Oracle, no idea about the others.
> Signed-off-by: Like Xu <likexu@tencent.com> > --- > arch/x86/kvm/pmu.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c > index edb89b51b383..c896328b2b5a 100644 > --- a/arch/x86/kvm/pmu.c > +++ b/arch/x86/kvm/pmu.c > @@ -526,12 +526,12 @@ int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data) > struct kvm_pmc *pmc; > u64 mask = fast_mode ? ~0u : ~0ull; > > - if (!pmu->version) > - return 1; > - > if (is_vmware_backdoor_pmc(idx)) > return kvm_pmu_rdpmc_vmware(vcpu, idx, data); > > + if (!pmu->version) > + return 1; > + > pmc = static_call(kvm_x86_pmu_rdpmc_ecx_to_pmc)(vcpu, idx, &mask); > if (!pmc) > return 1; > > base-commit: fff2e47e6c3b8050ca26656693caa857e3a8b740 > -- > 2.41.0 >
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