Messages in this thread | | | Date | Wed, 12 Dec 2018 02:37:53 +0300 | From | Alexey Dobriyan <> | Subject | Re: [RFC PATCH 4/4] x86/TSC: Use RDTSCP |
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> And I had a bit of a WTF moment, as in "WTF does > RDTSC have to do with a speculation protection barrier". > Does it actually make sense?
It doesn't. There was too much s/lfence/barrier_nospec/ apparently.
> + asm volatile(ALTERNATIVE_3("rdtsc", > + "mfence; rdtsc", X86_FEATURE_MFENCE_RDTSC, > + "lfence; rdtsc", X86_FEATURE_LFENCE_RDTSC, > + "rdtscp", X86_FEATURE_RDTSCP) > + : EAX_EDX_RET(val, low, high) > + /* RDTSCP clobbers ECX with MSR_TSC_AUX. */ > + :: "ecx");
I have a question: does alternatives ordering matter? CPU can have both features.
And other code in this file uses "c" for clobber.
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