From: Pavel Machek <pavel@ucw.cz>
To: Jiri Kosina <jikos@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>,
Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-arch@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
Greg KH <gregkh@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Elena Reshetova <elena.reshetova@intel.com>,
Alan Cox <alan@linux.intel.com>
Subject: Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
Date: Thu, 4 Jan 2018 21:40:00 +0100 [thread overview]
Message-ID: <20180104204000.GD10427@amd> (raw)
In-Reply-To: <alpine.LRH.2.00.1801040253410.27010@gjva.wvxbf.pm>
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Hi!
> > So this is in that same category, but yes, it's inconvenient.
>
> Disagreed, violently. CPU has to execute the instructions I ask it to
> execute, and if it executes *anything* else that reveals any information
> about the instructions that have *not* been executed, it's flawed.
I agree that's a flaw. Unfortunately... CPUs do execute instructions
you did not ask them to execute all the time.
Plus CPU designers forgot that cache state (and active row in DRAM) is
actually observable side-effect. ....and that's where we are today.
If you want, I have two systems with AMD Geode. One is PC. Neither is
very fast.
All the other general purpose CPUs I have -- and that includes
smartphones -- are likely out-of-order, and that means flawed.
So... situation is bad.
CPUs do execute intruction you did not ask them to execute. I don't
think that's reasonable to change.
I believe "right" fix would be for CPUs to treat even DRAM read as
side-effects, and adjust speculation accordingly. I'm not sure Intel/AMD
is going to do the right thing here.
Oh, I have an FPGA, too, if you want to play with RISC-V :-).
Best regards,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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next prev parent reply other threads:[~2018-01-04 20:40 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-03 22:38 [RFC PATCH 0/4] API for inhibiting speculative arbitrary read primitives Mark Rutland
2018-01-03 22:38 ` [RFC PATCH 1/4] asm-generic/barrier: add generic nospec helpers Mark Rutland
2018-01-04 12:00 ` Mark Rutland
2018-01-05 4:21 ` Dan Williams
2018-01-05 9:15 ` Mark Rutland
2018-01-03 22:38 ` [RFC PATCH 2/4] Documentation: document " Mark Rutland
2018-01-03 22:38 ` [RFC PATCH 3/4] arm64: implement nospec_{load,ptr}() Mark Rutland
2018-01-03 22:38 ` [RFC PATCH 4/4] bpf: inhibit speculated out-of-bounds pointers Mark Rutland
2018-01-03 23:45 ` Peter Zijlstra
2018-01-04 10:59 ` Mark Rutland
2018-01-04 0:15 ` [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier Dan Williams
2018-01-04 0:39 ` Linus Torvalds
2018-01-04 1:07 ` Alan Cox
2018-01-04 1:13 ` Dan Williams
2018-01-04 6:28 ` Julia Lawall
2018-01-04 17:58 ` Dan Williams
2018-01-04 19:26 ` Pavel Machek
2018-01-04 21:43 ` Dan Williams
2018-01-04 22:20 ` Linus Torvalds
2018-01-04 22:23 ` Linus Torvalds
2018-01-04 22:55 ` Alan Cox
2018-01-04 23:06 ` Linus Torvalds
2018-01-04 23:11 ` Alan Cox
2018-01-05 0:24 ` Dan Williams
2018-01-04 22:44 ` Pavel Machek
2018-01-04 23:12 ` Dan Williams
2018-01-04 23:21 ` Alan Cox
2018-01-04 23:33 ` Pavel Machek
2018-01-05 8:11 ` Julia Lawall
2018-01-04 1:27 ` Jiri Kosina
2018-01-04 1:41 ` Alan Cox
2018-01-04 1:47 ` Jiri Kosina
2018-01-04 19:39 ` Pavel Machek
2018-01-04 20:32 ` Alan Cox
2018-01-04 20:39 ` Jiri Kosina
2018-01-04 21:23 ` Alan Cox
2018-01-04 21:48 ` Pavel Machek
2018-01-04 1:51 ` Dan Williams
2018-01-04 1:54 ` Linus Torvalds
2018-01-04 3:10 ` Williams, Dan J
2018-01-04 4:44 ` Al Viro
2018-01-04 5:44 ` Dan Williams
2018-01-04 5:49 ` Dave Hansen
2018-01-04 5:50 ` Al Viro
2018-01-04 5:55 ` Al Viro
2018-01-04 6:42 ` Dan Williams
2018-01-04 5:01 ` Eric W. Biederman
2018-01-04 5:01 ` Eric W. Biederman
2018-01-04 6:32 ` Dan Williams
2018-01-04 14:54 ` Eric W. Biederman
2018-01-04 14:54 ` Eric W. Biederman
2018-01-04 16:39 ` Mark Rutland
2018-01-04 20:56 ` Pavel Machek
2018-01-04 11:47 ` Mark Rutland
2018-01-04 11:47 ` Mark Rutland
2018-01-04 11:47 ` Mark Rutland
2018-01-04 22:09 ` Dan Williams
2018-01-05 14:40 ` Mark Rutland
2018-01-05 16:44 ` Dan Williams
2018-01-05 18:05 ` Dan Williams
2018-01-04 1:59 ` Jiri Kosina
2018-01-04 2:15 ` Alan Cox
2018-01-04 3:12 ` Alexei Starovoitov
2018-01-04 9:16 ` Reshetova, Elena
2018-01-04 20:40 ` Pavel Machek [this message]
-- strict thread matches above, loose matches on Subject: below --
2018-01-05 10:33 Alexey Dobriyan
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