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    SubjectRe: [PATCH v8 11/11] x86/tdx: Handle CPUID via #VE
    On Mon, Oct 04, 2021 at 07:52:05PM -0700, Kuppuswamy Sathyanarayanan wrote:
    > +static u64 tdx_handle_cpuid(struct pt_regs *regs)
    > +{
    > + struct tdx_hypercall_output out = {0};
    > + u64 ret;
    > +
    > + /*
    > + * Emulate CPUID instruction via hypercall. More info about
    > + * ABI can be found in TDX Guest-Host-Communication Interface
    > + * (GHCI), section titled "VP.VMCALL<Instruction.CPUID>".
    > + */
    > + ret = _tdx_hypercall(EXIT_REASON_CPUID, regs->ax, regs->cx, 0, 0, &out);
    > +
    > + /*
    > + * As per TDX GHCI CPUID ABI, r12-r15 registers contains contents of
    > + * EAX, EBX, ECX, EDX registers after CPUID instruction execution.
    > + * So copy the register contents back to pt_regs.
    > + */
    > + regs->ax = out.r12;
    > + regs->bx = out.r13;
    > + regs->cx = out.r14;
    > + regs->dx = out.r15;

    Does it still make sense to save the regs if _tdx_hypercall() returns an
    error?

    > +
    > + return ret;

    Also I'm wondering about error handling for all these _tdx_hypercall()
    wrapper functions which are called by the #VE handler.

    First, there are some inconsistencies in whether and how they return the
    r10 error.

    - _tdx_halt() warns and doesn't return anything.

    - tdx_read_msr_safe() and tdx_write_msr_safe() convert all errors to -EIO.

    - tdx_handle_cpuid() returns the raw vmcall error.

    Second, as far as I can tell, the #VE handler doesn't check the actual
    return code value, other than checking for non-zero. Should it at least
    be printed in a warning?

    --
    Josh

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