linux-kernel - RE: [PATCH v6 06/13] x86/hyperv: Change vTOM handling to use standard coco mechanisms

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Date:   Sat, 25 Mar 2023 00:04:28 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Borislav Petkov <bp@...en8.de>
CC:     "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
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Subject: RE: [PATCH v6 06/13] x86/hyperv: Change vTOM handling to use standard
 coco mechanisms

From: Michael Kelley (LINUX) <mikelley@...rosoft.com>
> 
> From: Borislav Petkov <bp@...en8.de> Sent: Friday, March 24, 2023 8:49 AM
> >
> > On Thu, Mar 23, 2023 at 02:43:06PM +0100, Borislav Petkov wrote:
> > > Ok, lemme queue 1-2,4-6 as previously mentioned.
> >
> > With first six applied:
> >
> > arch/x86/coco/core.c:123:7: error: use of undeclared identifier 'sev_status'
> >                 if (sev_status & MSR_AMD64_SNP_VTOM)
> >                     ^
> > arch/x86/coco/core.c:139:7: error: use of undeclared identifier 'sev_status'
> >                 if (sev_status & MSR_AMD64_SNP_VTOM)
> >                     ^
> > 2 errors generated.
> > make[3]: *** [scripts/Makefile.build:252: arch/x86/coco/core.o] Error 1
> > make[2]: *** [scripts/Makefile.build:494: arch/x86/coco] Error 2
> > make[1]: *** [scripts/Makefile.build:494: arch/x86] Error 2
> > make[1]: *** Waiting for unfinished jobs....
> > make: *** [Makefile:2025: .] Error 2
> >
> > compiler is:
> >
> > Debian clang version 14.0.6-2
> > Target: x86_64-pc-linux-gnu
> > Thread model: posix
> > InstalledDir: /usr/bin
> >
> > .config is attached.
> >
> 
> OK, I see what went wrong.  I had tested with CONFIG_AMD_MEM_ENCRYPT=n
> and didn't see any compile problems.  It turns out in my test, arch/x86/coco/core.c
> wasn't built at all because I did not also have TDX configured, so I didn't see
> any errors.  But with CONFIG_INTEL_TDX_GUEST=y, coco/core.c gets built, and
> the error with undefined sev_status pops out.
> 
> The straightforward fix is somewhat ugly.  That's to put #ifdef
> CONFIG_AMD_MEM_ENCRYPT around the entire CC_VENDOR_AMD
> case in cc_mkenc() and in cc_mkdec().  Or put it just around the test of
> sev_status.
> 
> Perhaps a cleaner way would be to have a "vendor_subtype" variable
> declared in arch/x86/coco/core.c and tested instead of sev_status.
> That subtype variable would be set from hv_vtom_init(), maybe via
> a separate accessor function.  But didn't I recently see a patch that
> makes the existing "vendor" variable no longer static?   In that case
> just setting vendor_subtype without the accessor function may be
> OK.
> 
> What's your preference Boris?  I can spin a v7 of the patch series
> that fixes this, and that squashes the last two patches of the series
> per Lorenz Pieralisi's comments.
> 

Actually, a pretty clean approach is to #define sev_status 0ULL in
the #else /* !CONFIG_AMD_MEM_ENCRYPT */ half of
arch/x86/include/asm/mem_encrypt.h.   That's where the existing
extern statement is, and  sme_me_mask is already handled that way.

I'll respin the patch set with that approach.

Michael