From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: Tom Lendacky <Thomas.Lendacky@amd.com>,
LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
John Stultz <john.stultz@linaro.org>
Subject: Re: [RFC PATCH 4/4] x86/TSC: Use RDTSCP
Date: Wed, 12 Dec 2018 21:29:45 +0100 [thread overview]
Message-ID: <20181212202945.GH6653@zn.tnic> (raw)
In-Reply-To: <CALCETrWnYT1P0yPRkbubigvYRxesqYi4OJV-YxO9jzWqgCJBdg@mail.gmail.com>
On Wed, Dec 12, 2018 at 12:09:00PM -0800, Andy Lutomirski wrote:
> Also that the uarch doesn't turn:
>
> LFENCE
> RDTSC
> load some memory
>
> into a load followed a cycle later by RDTSC. If that happened, then
> some cooperating CPUs could observe time going backwards.
How so? Details?
Because I wouldn't be surprised at all if the logical CPUs on the same
node would see actually the same timestamp counter which is propagated
from the northbridge into the cores instead of maintaining it in each
core and having to synchronize it periodically.
But maybe you mean something completely different...
> But RDTSC has no dependencies, so, barring odd register renaming
> effects or similar, this isn't going to be a problem in practice.
Did you talk to hw guys about it? Because I don't see anything blocking
the CPU from reordering those...
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
next prev parent reply other threads:[~2018-12-12 20:29 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-11 22:23 [RFC PATCH 0/4] x86/alternative: Add ALTERNATIVE_3 Borislav Petkov
2018-12-11 22:23 ` [RFC PATCH 1/4] x86/alternatives: Add macro comments Borislav Petkov
2019-01-16 11:57 ` [tip:x86/alternatives] " tip-bot for Borislav Petkov
2018-12-11 22:23 ` [RFC PATCH 2/4] x86/alternatives: Print containing function Borislav Petkov
2019-01-16 11:58 ` [tip:x86/alternatives] " tip-bot for Borislav Petkov
2018-12-11 22:23 ` [RFC PATCH 3/4] x86/alternatives: Add an ALTERNATIVE_3() macro Borislav Petkov
2019-01-16 11:59 ` [tip:x86/alternatives] " tip-bot for 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 [this message]
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
-- strict thread matches above, loose matches on Subject: below --
2018-12-11 23:37 Alexey Dobriyan
2018-12-11 23:43 ` Borislav Petkov
2018-12-12 0:06 ` Borislav Petkov
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