Re: [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm

[Paolo Bonzini]

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@xxxxxxxxxxxxxxx
> > 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