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    SubjectRe: [PATCH Part1 RFC v4 22/36] x86/sev: move MSR-based VMGEXITs for CPUID to helper
    On Thu, Aug 19, 2021 at 11:45:35AM +0200, Borislav Petkov wrote:
    > Finally drop this bouncing npmccallum at RH email address from the Cc
    > list.
    >
    > On Wed, Jul 07, 2021 at 01:14:52PM -0500, Brijesh Singh wrote:
    > > From: Michael Roth <michael.roth@amd.com>
    > >
    > > This code will also be used later for SEV-SNP-validated CPUID code in
    > > some cases, so move it to a common helper.
    > >
    > > Signed-off-by: Michael Roth <michael.roth@amd.com>
    > > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    > > ---
    > > arch/x86/kernel/sev-shared.c | 84 +++++++++++++++++++++++++-----------
    > > 1 file changed, 58 insertions(+), 26 deletions(-)
    > >
    > > diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
    > > index be4025f14b4f..4884de256a49 100644
    > > --- a/arch/x86/kernel/sev-shared.c
    > > +++ b/arch/x86/kernel/sev-shared.c
    > > @@ -184,6 +184,58 @@ static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
    > > return ret;
    > > }
    > >
    > > +static int sev_es_cpuid_msr_proto(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
    >
    > Since it is not only SEV-ES, then it should be prefixed with "sev_" like
    > we do for the other such functions. I guess simply
    >
    > sev_cpuid()
    >
    > ?

    That makes sense, but I think it helps in making sense of the security
    aspects of the code to know that sev_cpuid() would be fetching cpuid
    information from the hypervisor. "msr_proto" is meant to be an indicator
    that it will be using the GHCB MSR protocol to do it, but maybe just
    "_hyp" is enough to get the idea across? I use the convention elsewhere
    in the series as well.

    So sev_cpuid_hyp() maybe?

    >
    > > + u32 *ecx, u32 *edx)
    > > +{
    > > + u64 val;
    > > +
    > > + if (eax) {
    >
    > What's the protection for? Is it ever going to be called with NULL ptrs
    > for the regs? That's not the case in this patchset at least...

    In "enable SEV-SNP-validated CPUID in #VC handler", it does:

    sev_snp_cpuid() -> sev_snp_cpuid_hyp(),

    which will call this with NULL e{a,b,c,d}x arguments in some cases. There
    are enough call-sites in sev_snp_cpuid() that it seemed worthwhile to
    add the guards so we wouldn't need to declare dummy variables for arguments.

    >
    > --
    > Regards/Gruss,
    > Boris.
    >
    > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpeople.kernel.org%2Ftglx%2Fnotes-about-netiquette&amp;data=04%7C01%7Cmichael.roth%40amd.com%7C567fab11117b4072171508d962f6043a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637649631103094962%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=fg87GYa5RX5ea54IwYLzwXupt6VVyLM%2BkyMnGB3S0wQ%3D&amp;reserved=0

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