linux-kernel - RE: [Patch v4 06/13] x86/hyperv: Change vTOM handling to use standard coco mechanisms

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Date:   Mon, 9 Jan 2023 17:37:00 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
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Subject: RE: [Patch v4 06/13] x86/hyperv: Change vTOM handling to use standard
 coco mechanisms

From: Borislav Petkov <bp@...en8.de> Sent: Monday, January 9, 2023 8:39 AM
> 
[snip]

> > diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
> > index 49b44f8..c361c52 100644
> > --- a/arch/x86/coco/core.c
> > +++ b/arch/x86/coco/core.c
> > @@ -44,6 +44,24 @@ static bool intel_cc_platform_has(enum cc_attr attr)
> >  static bool amd_cc_platform_has(enum cc_attr attr)
> >  {
> >  #ifdef CONFIG_AMD_MEM_ENCRYPT
> > +
> > +	/*
> > +	 * Handle the SEV-SNP vTOM case where sme_me_mask must be zero,
> > +	 * and the other levels of SME/SEV functionality, including C-bit
> > +	 * based SEV-SNP, must not be enabled.
> > +	 */
> > +	if (sev_status & MSR_AMD64_SNP_VTOM_ENABLED) {
> 
> 		return amd_cc_platform_vtom();
> 
> or so and then stick that switch in there.
> 
> This way it looks kinda grafted in front and with a function call with a telling
> name it says it is a special case...
> 
> > +		switch (attr) {
> > +		case CC_ATTR_GUEST_MEM_ENCRYPT:
> > +		case CC_ATTR_MEM_ENCRYPT:
> > +		case CC_ATTR_ACCESS_IOAPIC_ENCRYPTED:
> > +			return true;
> > +		default:
> > +			return false;
> > +		}
> > +	}
> 
> The rest looks kinda nice, I gotta say. I can't complain. :)
> 

OK.  I have no objection to putting that code in a separate "helper"
function.  The only slight messiness is that the helper function must
be separately wrapped in #ifdef CONFIG_AMD_MEM_ENCRYPT, or
marked __maybe_unused.

Michael