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

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Message-ID: <BYAPR21MB16886692DF02269DE1D0C4A5D7849@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Fri, 24 Mar 2023 19:36:02 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Borislav Petkov <bp@...en8.de>
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Subject: RE: [PATCH v6 06/13] x86/hyperv: Change vTOM handling to use standard
 coco mechanisms

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.

Michael