Messages in this thread | | | Date | Wed, 6 Oct 2021 18:20:41 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature |
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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.
https://people.kernel.org/tglx/notes-about-netiquette
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