From: Alexey Dobriyan <adobriyan@gmail.com>
To: luto@kernel.org
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@suse.de,
thomas.lendacky@amd.com, hpa@zytor.com, john.stultz@linaro.org,
x86@kernel.org
Subject: Re: [RFC PATCH 4/4] x86/TSC: Use RDTSCP
Date: Wed, 12 Dec 2018 02:37:53 +0300 [thread overview]
Message-ID: <20181211233753.GA26593@avx2> (raw)
> 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.
next reply other threads:[~2018-12-11 23:37 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-11 23:37 Alexey Dobriyan [this message]
2018-12-11 23:43 ` [RFC PATCH 4/4] x86/TSC: Use RDTSCP Borislav Petkov
2018-12-12 0:06 ` Borislav Petkov
-- strict thread matches above, loose matches on Subject: below --
2018-12-11 22:23 [RFC PATCH 0/4] x86/alternative: Add ALTERNATIVE_3 Borislav Petkov
2018-12-11 22:23 ` [RFC PATCH 4/4] x86/TSC: Use RDTSCP Borislav Petkov
2018-12-11 22:59 ` Andy Lutomirski
2018-12-11 23:12 ` Lendacky, Thomas
2018-12-11 23:39 ` Borislav Petkov
2018-12-12 2:24 ` Andy Lutomirski
2018-12-12 9:59 ` Peter Zijlstra
2018-12-12 12:02 ` Andrea Parri
2018-12-12 10:08 ` Borislav Petkov
2018-12-12 18:07 ` Andy Lutomirski
2018-12-12 18:44 ` Borislav Petkov
2018-12-12 18:50 ` Andy Lutomirski
2018-12-12 20:00 ` Borislav Petkov
2018-12-12 20:09 ` Andy Lutomirski
2018-12-12 20:29 ` Borislav Petkov
2018-12-14 13:39 ` David Laight
2018-12-15 18:53 ` Andy Lutomirski
2018-12-12 14:15 ` Lendacky, Thomas
2018-12-12 14:18 ` Lendacky, Thomas
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