Re: [PATCH Part1 v5 32/38] x86/sev: enable SEV-SNP-validated CPUID in #VC handlers

Michael Roth
2021-09-01T01:17:13Z

On Tue, Aug 31, 2021 at 06:22:44PM +0200, Borislav Petkov wrote:
> On Fri, Aug 27, 2021 at 01:32:40PM -0500, Michael Roth wrote:
> > If the memory is allocated in boot/compressed/mem_encrypt.S, wouldn't
> > kernel proper still need to create a static buffer for its copy?
>
> Just like the other variables like sme_me_mask etc that file allocates
> at the bottom. Or do you have a better idea?

What did you think of the suggestion of defining it in sev-shared.c
as a static buffer/struct as __ro_after_init? It would be nice to
declare/reserve the memory in one place. Another benefit is it doesn't
need to be exported, and could just be local with all the other
snp_cpuid* helpers that access it in sev-shared.c

>
> > Would that be a reasonable approach for v6?
>
> I don't like the ifdeffery one bit, TBH. I guess you should split it
> and have a boot/compressed page and a kernel proper one and keep 'em
> separate. That should make everything nice and clean at the cost of 2*4K
> which is nothing nowadays.

I think I can address the ifdeffery by splitting the boot/proper routines
into separate self-contained routines (and maybe move them out into
boot/compressed/sev.c and kernel/sev.c, respectively), then having them
just initialize the table pointer and create the copy using a common setter
function, e.g.

snp_cpuid_table_create(cc_blob, fixup_offset)

and for boot/compressed.c fixup_offset would just be passed in as 0.

>
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
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