On Tue, Jan 9, 2018 at 4:31 PM, Andi Kleen <[email protected]> wrote:
>
> The following patch fixes it for me. Something doesn't
> seem to work with ALTERNATIVE_2. It adds only a few bytes
> more code, so seems acceptable.
Ugh. It's kind of stupid, though.
Why is the code sequence not simply:
ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE_AMD
ALTERNATIVE __stringify(jmp *\reg), __stringify(RETPOLINE_JMP \reg),
X86_FEATURE_RETPOLINE
ie make that X86_FEATURE_RETPOLINE_AMD _only_ emit the "lfence", and
simply fall through to what will be the "jmp *\reg" of the
non-RETPOLINE version.
Then just make sure X86_FEATURE_RETPOLINE_AMD disables X86_FEATURE_RETPOLINE.
That is both simpler an dsmaller, no?
Linus
