Re: [PATCH V2 03/14] x86/set_memory: Add x86_set_memory_enc static call support

Peter Zijlstra
2021-08-05T14:23:51Z

On Thu, Aug 05, 2021 at 10:05:17PM +0800, Tianyu Lan wrote:
> static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
> {
> + return static_call(x86_set_memory_enc)(addr, numpages, enc);
> }

Hurpmh... So with a bit of 'luck' you get code-gen like:

__set_memory_enc_dec:
jmp __SCT_x86_set_memory_enc;

set_memory_encrypted:
mov $1, %rdx
jmp __set_memory_enc_dec

set_memory_decrypted:
mov $0, %rdx
jmp __set_memory_enc_dec

Which, to me, seems exceedingly daft. Best to make all 3 of those
inlines and use EXPORT_STATIC_CALL_TRAMP_GPL(x86_set_memory_enc) or
something.

This is assuming any of this is actually performance critical, based off
of this using static_call() to begin with.