Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature

[Borislav Petkov]

On Wed, Oct 06, 2021 at 08:43:48AM -0700, Kuppuswamy, Sathyanarayanan wrote:
> Yes. But, Joerg Roedel in his review recommended using variable
> similar to sme_me_mask to avoid function call in Intel platform in
> cc_platform_has().

That would normally make sense if this were a fast path. But I don't see
that being one. Besides, the subsequent runs will be the function call +
a couple of instructions:

# arch/x86/kernel/tdx.c:22: 	if (tdx_guest >= 0)
	movl	tdx_guest(%rip), %eax	# tdx_guest,
	testl	%eax, %eax	#
	jns	.L11	#,

...

.L11:
# arch/x86/kernel/tdx.c:23: 		return tdx_guest;
	setne	%al	#, <retval>
# arch/x86/kernel/tdx.c:35: }
	ret

which is not the end of the world.

And it if it is really used in a fast path, then we can do a static
branch etc.

Thx.

-- 
Regards/Gruss,
    Boris.

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