From: Linus Torvalds <torvalds@linux-foundation.org>
To: Borislav Petkov <bp@alien8.de>
Cc: David Howells <dhowells@redhat.com>,
kernel test robot <oliver.sang@intel.com>,
oe-lkp@lists.linux.dev, lkp@intel.com,
linux-kernel@vger.kernel.org,
Christian Brauner <brauner@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
Christian Brauner <christian@brauner.io>,
Matthew Wilcox <willy@infradead.org>,
David Laight <David.Laight@aculab.com>,
ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com
Subject: Re: [linus:master] [iov_iter] c9eec08bac: vm-scalability.throughput -16.9% regression
Date: Wed, 15 Nov 2023 14:15:46 -0500 [thread overview]
Message-ID: <CAHk-=whFW+uWOmOtRNh0What_fu8Xo8KF2+EeUH1kn4qFxGAhA@mail.gmail.com> (raw)
In-Reply-To: <20231115190938.GGZVUXcuUjI3i1JRAB@fat_crate.local>
On Wed, 15 Nov 2023 at 14:10, Borislav Petkov <bp@alien8.de> wrote:
>
> Should we define an alternative_memcpy() which is used *only* during
> rewriting so that this becomes a non-issue?
Yeah, I think the instruction rewriting should use something that
explicitly cannot possibility itself need rewriting, and a plain
'memcpy()' is obviously that.
The good news is that at least things like structure copies would
*not* trigger that alternative, so it's only explicit memcpy() calls
that my patch changes. But I would not be surprised if instruction
rewriting does that. I didn't actually check.
> Yours looks simple enough and makes sense. Lemme poke at it a bit in the
> coming days and see what happens.
Note that it has a nasty interaction with fortify-source, which is why
it has that hacky "#undef memcpy" in that unrelated header.
Also note that I was being very very lazy in how I re-used the
"rep_movs_alternative" function that we already have. And it's
actually a bad laziness, because our existing rep_movs_alternative
does the exception handling for user mode faults.
We don't actually want exception handling for 'memcpy()', because it
could hide bugs. If a memcpy() gets a bad pointer, we want the oops,
not a partial copy.
So my patch really is broken. It might happen to work when everything
else goes right, and it's small, but it is very much a "proof of
concept" rather than something that is actually acceptable.
Linus
next prev parent reply other threads:[~2023-11-15 19:16 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-07 1:40 [linus:master] [iov_iter] c9eec08bac: vm-scalability.throughput -16.9% regression kernel test robot
2023-11-15 12:48 ` David Howells
2023-11-15 13:18 ` David Howells
2023-11-15 15:20 ` David Howells
2023-11-15 16:53 ` Linus Torvalds
2023-11-15 17:38 ` Linus Torvalds
2023-11-15 18:38 ` Linus Torvalds
2023-11-15 19:09 ` Borislav Petkov
2023-11-15 19:15 ` Linus Torvalds [this message]
2023-11-15 20:07 ` Linus Torvalds
2023-11-16 10:07 ` David Laight
2023-11-16 10:14 ` David Howells
2023-11-16 11:38 ` David Laight
2023-11-15 19:26 ` Linus Torvalds
2023-11-16 15:44 ` Borislav Petkov
2023-11-16 16:48 ` Linus Torvalds
2023-11-16 16:58 ` David Laight
2023-11-17 11:44 ` Borislav Petkov
2023-11-17 12:09 ` Jakub Jelinek
2023-11-17 12:18 ` Borislav Petkov
2023-11-17 13:09 ` David Laight
2023-11-17 13:36 ` Linus Torvalds
2023-11-17 15:20 ` David Laight
2023-11-16 16:44 ` David Howells
2023-11-17 11:35 ` Borislav Petkov
2023-11-17 14:12 ` David Howells
2023-11-17 16:09 ` Borislav Petkov
2023-11-17 16:32 ` Linus Torvalds
2023-11-17 16:44 ` Linus Torvalds
2023-11-17 19:12 ` Borislav Petkov
2023-11-17 21:57 ` Linus Torvalds
2023-11-20 13:32 ` David Howells
2023-11-20 16:06 ` Linus Torvalds
2023-11-20 16:09 ` David Laight
2023-11-15 21:43 ` David Howells
2023-11-15 21:50 ` Linus Torvalds
2023-11-15 21:59 ` Borislav Petkov
2023-11-20 11:52 ` Borislav Petkov
2023-11-15 22:59 ` David Howells
2023-11-16 3:26 ` Linus Torvalds
2023-11-16 16:55 ` David Laight
2023-11-16 17:24 ` Linus Torvalds
2023-11-16 22:53 ` David Laight
2023-11-16 21:09 ` David Howells
2023-11-16 22:36 ` Linus Torvalds
2023-11-15 18:35 ` David Howells
2023-11-15 18:45 ` Linus Torvalds
2023-11-15 19:09 ` Linus Torvalds
2023-11-15 20:54 ` David Howells
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