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SubjectRe: [PATCH 08/10] x86/tdx: Unify TDX_HYPERCALL and TDX_MODULE_CALL assembly


<snip>

> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 0f16ba52ae62..a5e77893b2c0 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -51,13 +51,38 @@
>
> #define TDREPORT_SUBTYPE_0 0
>
> +/* Called from __tdx_hypercall() for unrecoverable failure */
> +static noinstr void __tdx_hypercall_failed(void)
> +{
> + instrumentation_begin();
> + panic("TDVMCALL failed. TDX module bug?");
> +}

So what's the deal with this instrumentation here. The instruction is
noinstr, so you want to make just the panic call itself instrumentable?,
if so where's the instrumentation_end() cal;?No instrumentation_end()
call. Actually is this complexity really worth it for the failure case?

AFAICS there is a single call site for __tdx_hypercall_failed so why
noot call panic() directly ?

> +
> +static inline u64 __tdx_hypercall(struct tdx_module_args *args)
> +{
> + u64 ret;
> +
> + args->rcx = TDVMCALL_EXPOSE_REGS_MASK;
> + ret = __tdcall_saved_ret(TDG_VP_VMCALL, args);
> +
> + /*
> + * RAX!=0 indicates a failure of the TDVMCALL mechanism itself and that

nit: Why mention the register explicitly, just say that if
__tdcall_saved_ret returns non-zero ....

> + * something has gone horribly wrong with the TDX module.
> + */
> + if (ret)
> + __tdx_hypercall_failed();
> +
> + /* The return status of the hypercall itself is in R10. */
> + return args->r10;
> +}
> +
> /*
> - * Wrapper for standard use of __tdx_hypercall with no output aside from
> - * return code.
> + * Wrapper for standard use of __tdx_hypercall() w/o needing any output
> + * register except the return code.
> */
> static inline u64 _tdx_hypercall(u64 fn, u64 r12, u64 r13, u64 r14, u64 r15)
> {
> - struct tdx_hypercall_args args = {
> + struct tdx_module_args args = {
> .r10 = TDX_HYPERCALL_STANDARD,
> .r11 = fn,
> .r12 = r12,

<snip>

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