Re: [PATCH v6 7/7] x86/vmware: Add TDX hypercall support

[H. Peter Anvin]

On January 22, 2024 8:32:22 AM PST, Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
>On 1/9/24 00:40, Alexey Makhalov wrote:
>> +#ifdef CONFIG_INTEL_TDX_GUEST
>> +unsigned long vmware_tdx_hypercall(unsigned long cmd,
>> +				   struct tdx_module_args *args)
>> +{
>> +	if (!hypervisor_is_type(X86_HYPER_VMWARE))
>> +		return ULONG_MAX;
>> +
>> +	if (cmd & ~VMWARE_CMD_MASK) {
>> +		pr_warn_once("Out of range command %lx\n", cmd);
>> +		return ULONG_MAX;
>> +	}
>> +
>> +	args->r10 = VMWARE_TDX_VENDOR_LEAF;
>> +	args->r11 = VMWARE_TDX_HCALL_FUNC;
>> +	args->r12 = VMWARE_HYPERVISOR_MAGIC;
>> +	args->r13 = cmd;
>> +	args->r15 = 0; /* CPL */
>> +
>> +	__tdx_hypercall(args);
>> +
>> +	return args->r12;
>> +}
>> +EXPORT_SYMBOL_GPL(vmware_tdx_hypercall);
>> +#endif
>
>This is the kind of wrapper that I was hoping for.  Thanks.
>
>Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>

I'm slightly confused by this TBH.

Why are the arguments passed in as a structure, which is modified by the wrapper to boot? This is analogous to a system call interface.

Furthermore, this is an out-of-line function; it should never be called with !X86_HYPER_VMWARE or you are introducing overhead for other hypervisors; I believe a pr_warn_once() is in order at least, just as you have for the out-of-range test.