Messages in this thread | | | From | Linus Torvalds <> | Date | Tue, 9 Jan 2018 16:39:19 -0800 | Subject | Re: [PATCH] x86/retpoline: Fix NOSPEC_JMP for tip |
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On Tue, Jan 9, 2018 at 4:31 PM, Andi Kleen <andi@firstfloor.org> 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
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