From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Luck, Tony" <tony.luck@intel.com>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>, stable <stable@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Paul Mackerras <paulus@samba.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Erwin Tsaur <erwin.tsaur@intel.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
linux-nvdimm <linux-nvdimm@lists.01.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe()
Date: Thu, 30 Apr 2020 18:20:39 -0700 [thread overview]
Message-ID: <D47C71D3-349B-49C4-9945-330C9F42A3E0@amacapital.net> (raw)
In-Reply-To: <CAHk-=wh1SPyuGkTkQESsacwKTpjWd=_-KwoCK5o=SuC3yMdf7A@mail.gmail.com>
> On Apr 30, 2020, at 5:25 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>
> It wasn't clear how "copy_to_mc()" could ever fault. Poisoning
> after-the-fact? Why would that be preferable to just mapping a dummy
> page?
If the kernel gets an async memory error and maps a dummy page, then subsequent reads will subsequently succeed and return garbage when they should fail. If x86 had write-only pages, we could map a dummy write-only page. But we don’t, so I think we’re stuck.
As for naming the kind of memory we’re taking about, ISTM there are two classes: DAX and monstrous memory-mapped non-persistent cache devices. Both could be Optane, I suppose.
But I also think it’s legitimate to use these accessors to increase the chance of surviving a failure of normal memory. If a normal page happens to be page cache when it fails and if page cache access use these fancy accessors, then we might actually survive a failure.
We could be ambitious: declare that all page cache and all get_user_page’d memory should use the new accessors. I doubt we’ll ever really succeed due to magical things like rseq and anything that thinks that users can set up their own memory as a kernel-accessed ring buffer, but I suppose we could try.
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next prev parent reply other threads:[~2020-05-01 1:20 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-30 8:24 [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe() Dan Williams
2020-04-30 8:25 ` [PATCH v2 1/2] copy_safe: Rename memcpy_mcsafe() to copy_safe() Dan Williams
2020-04-30 8:25 ` [PATCH v2 2/2] x86/copy_safe: Introduce copy_safe_fast() Dan Williams
2020-04-30 14:02 ` [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe() Linus Torvalds
2020-04-30 16:51 ` Andy Lutomirski
2020-04-30 17:17 ` Linus Torvalds
2020-04-30 18:42 ` Andy Lutomirski
2020-04-30 19:22 ` Luck, Tony
2020-04-30 19:50 ` Linus Torvalds
2020-04-30 20:25 ` Luck, Tony
2020-04-30 23:52 ` Dan Williams
2020-05-01 0:10 ` Linus Torvalds
2020-05-01 0:23 ` Andy Lutomirski
2020-05-01 0:39 ` Linus Torvalds
2020-05-01 1:10 ` Andy Lutomirski
2020-05-01 14:09 ` Luck, Tony
2020-05-03 0:29 ` Andy Lutomirski
2020-05-04 20:05 ` Luck, Tony
2020-05-04 20:26 ` Andy Lutomirski
2020-05-04 21:30 ` Dan Williams
2020-05-01 0:24 ` Linus Torvalds
2020-05-01 1:20 ` Andy Lutomirski [this message]
2020-05-01 1:21 ` Dan Williams
2020-05-01 18:28 ` Linus Torvalds
2020-05-01 20:17 ` Dave Hansen
2020-05-03 12:57 ` David Laight
2020-05-04 18:33 ` Dan Williams
2020-05-11 15:24 ` Vivek Goyal
2020-04-30 19:51 ` Dan Williams
2020-04-30 20:07 ` Andy Lutomirski
2020-05-01 7:46 ` David Laight
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