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    SubjectRe: [PATCH v9 22/43] x86/sev: Move MSR-based VMGEXITs for CPUID to helper
    On Fri, Jan 28, 2022 at 11:17:43AM -0600, 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.

    Suggested-by: Sean Christopherson <seanjc@google.com>

    unless he really doesn't want to be the "suggestor" :)

    > Signed-off-by: Michael Roth <michael.roth@amd.com>
    > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    > ---
    > arch/x86/kernel/sev-shared.c | 62 +++++++++++++++++++++---------------
    > 1 file changed, 36 insertions(+), 26 deletions(-)
    >
    > diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
    > index 3aaef1a18ffe..633f1f93b6e1 100644
    > --- a/arch/x86/kernel/sev-shared.c
    > +++ b/arch/x86/kernel/sev-shared.c
    > @@ -194,6 +194,36 @@ enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
    > return verify_exception_info(ghcb, ctxt);
    > }
    >
    > +static int __sev_cpuid_hv(u32 func, int reg_idx, u32 *reg)
    > +{
    > + u64 val;
    > +
    > + if (!reg)
    > + return 0;

    I don't know what that's supposed to catch? In case callers are
    interested only in some subset of the CPUID leaf?

    Meh, I guess...

    > + sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(func, reg_idx));
    > + VMGEXIT();
    > + val = sev_es_rd_ghcb_msr();
    > + if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
    > + return -EIO;
    > +
    > + *reg = (val >> 32);
    > +
    > + return 0;
    > +}
    > +
    > +static int sev_cpuid_hv(u32 func, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
    > +{
    > + int ret;
    > +
    > + ret = __sev_cpuid_hv(func, GHCB_CPUID_REQ_EAX, eax);
    > + ret = ret ? : __sev_cpuid_hv(func, GHCB_CPUID_REQ_EBX, ebx);
    > + ret = ret ? : __sev_cpuid_hv(func, GHCB_CPUID_REQ_ECX, ecx);
    > + ret = ret ? : __sev_cpuid_hv(func, GHCB_CPUID_REQ_EDX, edx);

    You can format that this way:

    ret = __sev_cpuid_hv(func, GHCB_CPUID_REQ_EAX, eax);
    ret = ret ? : __sev_cpuid_hv(func, GHCB_CPUID_REQ_EBX, ebx);
    ret = ret ? : __sev_cpuid_hv(func, GHCB_CPUID_REQ_ECX, ecx);
    ret = ret ? : __sev_cpuid_hv(func, GHCB_CPUID_REQ_EDX, edx);


    and then it is visible at a quick glance what this does, due to the
    regularity.

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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