Re: [PATCH v4 1/4] x86/cpufeatures: Add CPUID feature bit for Idle HLT intercept

[Sean Christopherson <seanjc@google.com>]

On Tue, Oct 22, 2024, Borislav Petkov wrote:
> On Tue, Oct 22, 2024 at 05:48:07AM +0000, Manali Shukla wrote:
> > From: Manali Shukla <Manali.Shukla@amd.com>
> > 
> > The Idle HLT Intercept feature allows for the HLT instruction
> > execution by a vCPU to be intercepted by the hypervisor only if there
> > are no pending events (V_INTR and V_NMI) for the vCPU. When the vCPU
> > is expected to service the pending events (V_INTR and V_NMI), the Idle
> > HLT intercept won’t trigger. The feature allows the hypervisor to
> > determine if the vCPU is idle and reduces wasteful VMEXITs.
> > 
> > In addition to the aforementioned use case, the Idle HLT intercept
> > feature is also used for enlightened guests who aim to securely manage
> > events without the hypervisor’s awareness. If a HLT occurs while
> > a virtual event is pending and the hypervisor is unaware of this
> > pending event (as could be the case with enlightened guests), the
> > absence of the Idle HLT intercept feature could result in a vCPU being
> > suspended indefinitely.
> > 
> > Presence of Idle HLT intercept feature for guests is indicated via CPUID
> > function 0x8000000A_EDX[30].
> > 
> > Signed-off-by: Manali Shukla <Manali.Shukla@amd.com>
> > Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
> > ---
> >  arch/x86/include/asm/cpufeatures.h | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> > index dd4682857c12..7461a49e1045 100644
> > --- a/arch/x86/include/asm/cpufeatures.h
> > +++ b/arch/x86/include/asm/cpufeatures.h
> > @@ -382,6 +382,7 @@
> >  #define X86_FEATURE_V_SPEC_CTRL		(15*32+20) /* "v_spec_ctrl" Virtual SPEC_CTRL */
> >  #define X86_FEATURE_VNMI		(15*32+25) /* "vnmi" Virtual NMI */
> >  #define X86_FEATURE_SVME_ADDR_CHK	(15*32+28) /* SVME addr check */
> > +#define X86_FEATURE_IDLE_HLT		(15*32+30) /* "" IDLE HLT intercept */
> 
> Whoever commits this, you can remove the "" in the comment now as they're not
> needed anymore.

Ya, will do.