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SubjectRe: [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm
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On 11/8/22 21:54, Sean Christopherson wrote:
> On Tue, Nov 08, 2022, Paolo Bonzini wrote:
>> Since registers are reachable through vcpu_svm, and we will
>> need to access more fields of that struct, pass it instead
>> of the regs[] array.
>>
>> No functional change intended.
>>
>> Cc: stable@vger.kernel.org
>> Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
>
> I don't think a Fixes: tag for a pure nop patch is fair to the original commit.

That's for the sake of correct tracking in stable@, still it's not the
right commit to point at:

- f14eec0a3203 did not move the RSB stuffing before the GSBASE restore,
the code before was:

vmexit_fill_RSB();
#ifdef CONFIG_X86_64
wrmsrl(MSR_GS_BASE, svm->host.gs_base);
#else

- anyway it wasn't really buggy at the time: it's only in -next that
FILL_RETURN_BUFFER uses percpu data, because alternatives take care of
the X86_FEATURE_* checks

The real reason to do all this is to access the percpu host spec_ctrl,
which in turn is needed for retbleed. I'll point the Fixes tag to
a149180fbcf3 ("x86: Add magic AMD return-thunk") instead, again just for
the sake of tracking releases that need the change to full fix retbleed.

Paolo

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