From: "Luck, Tony" <tony.luck@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: 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 13:25:16 -0700 [thread overview]
Message-ID: <20200430202516.GA26147@agluck-desk2.amr.corp.intel.com> (raw)
In-Reply-To: <CAHk-=wg0Sza8uzQHzJbdt7FFc7bRK+o1BB=VBUGrQEvVv6+23w@mail.gmail.com>
On Thu, Apr 30, 2020 at 12:50:40PM -0700, Linus Torvalds wrote:
I see your point about the namimg being important. I think Dan's
case is indeed "copy from pmem to user" where only options for faulting
are #MC on the source addresses, and #PF on the destination.
> The only *fundamental* access would likely be a single read/write
> operation, not a copy operation. Think "get_user()" instead of
> "copy_from_user()". Even there you get combinatorial explosions with
> access sizes, but you can often generate those automatically or with
> simple patterns, and then you can build up the copy functions from
> that if you really need to.
That's maybe very clean. But it looks like it would be hard to build
a high performance interface on top of that primitive. Remember that
for Dan's copy 99.999999999367673%[1] of copies will not hit a machine
check on the read from pmem.
Dan wants (whatever the function name) to get to a "REP MOVS" with an
exception table entry to handle the cases where there is a fault.
-Tony
[1] Likely several more '9's in there
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WARNING: multiple messages have this Message-ID (diff)
From: "Luck, Tony" <tony.luck@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
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 13:25:16 -0700 [thread overview]
Message-ID: <20200430202516.GA26147@agluck-desk2.amr.corp.intel.com> (raw)
In-Reply-To: <CAHk-=wg0Sza8uzQHzJbdt7FFc7bRK+o1BB=VBUGrQEvVv6+23w@mail.gmail.com>
On Thu, Apr 30, 2020 at 12:50:40PM -0700, Linus Torvalds wrote:
I see your point about the namimg being important. I think Dan's
case is indeed "copy from pmem to user" where only options for faulting
are #MC on the source addresses, and #PF on the destination.
> The only *fundamental* access would likely be a single read/write
> operation, not a copy operation. Think "get_user()" instead of
> "copy_from_user()". Even there you get combinatorial explosions with
> access sizes, but you can often generate those automatically or with
> simple patterns, and then you can build up the copy functions from
> that if you really need to.
That's maybe very clean. But it looks like it would be hard to build
a high performance interface on top of that primitive. Remember that
for Dan's copy 99.999999999367673%[1] of copies will not hit a machine
check on the read from pmem.
Dan wants (whatever the function name) to get to a "REP MOVS" with an
exception table entry to handle the cases where there is a fault.
-Tony
[1] Likely several more '9's in there
next prev parent reply other threads:[~2020-04-30 20:25 UTC|newest]
Thread overview: 64+ 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 8:24 ` 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 ` Dan Williams
2020-05-01 2:55 ` Sasha Levin
2020-04-30 8:25 ` [PATCH v2 2/2] x86/copy_safe: Introduce copy_safe_fast() Dan Williams
2020-04-30 8:25 ` Dan Williams
2020-05-01 2:55 ` Sasha Levin
2020-04-30 14:02 ` [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe() Linus Torvalds
2020-04-30 14:02 ` Linus Torvalds
2020-04-30 16:51 ` Andy Lutomirski
2020-04-30 16:51 ` Andy Lutomirski
2020-04-30 17:17 ` Linus Torvalds
2020-04-30 17:17 ` Linus Torvalds
2020-04-30 18:42 ` Andy Lutomirski
2020-04-30 18:42 ` Andy Lutomirski
2020-04-30 19:22 ` Luck, Tony
2020-04-30 19:22 ` Luck, Tony
2020-04-30 19:50 ` Linus Torvalds
2020-04-30 19:50 ` Linus Torvalds
2020-04-30 20:25 ` Luck, Tony [this message]
2020-04-30 20:25 ` Luck, Tony
2020-04-30 23:52 ` Dan Williams
2020-04-30 23:52 ` Dan Williams
2020-05-01 0:10 ` Linus Torvalds
2020-05-01 0:10 ` Linus Torvalds
2020-05-01 0:23 ` Andy Lutomirski
2020-05-01 0:23 ` Andy Lutomirski
2020-05-01 0:39 ` Linus Torvalds
2020-05-01 0:39 ` Linus Torvalds
2020-05-01 1:10 ` Andy Lutomirski
2020-05-01 1:10 ` Andy Lutomirski
2020-05-01 14:09 ` Luck, Tony
2020-05-01 14:09 ` Luck, Tony
2020-05-03 0:29 ` Andy Lutomirski
2020-05-03 0:29 ` Andy Lutomirski
2020-05-04 20:05 ` Luck, Tony
2020-05-04 20:05 ` Luck, Tony
2020-05-04 20:26 ` Andy Lutomirski
2020-05-04 20:26 ` Andy Lutomirski
2020-05-04 21:30 ` Dan Williams
2020-05-04 21:30 ` Dan Williams
2020-05-01 0:24 ` Linus Torvalds
2020-05-01 0:24 ` Linus Torvalds
2020-05-01 1:20 ` Andy Lutomirski
2020-05-01 1:20 ` Andy Lutomirski
2020-05-01 1:21 ` Dan Williams
2020-05-01 1:21 ` Dan Williams
2020-05-01 18:28 ` Linus Torvalds
2020-05-01 18:28 ` Linus Torvalds
2020-05-01 20:17 ` Dave Hansen
2020-05-01 20:17 ` Dave Hansen
2020-05-03 12:57 ` David Laight
2020-05-03 12:57 ` David Laight
2020-05-04 18:33 ` Dan Williams
2020-05-04 18:33 ` Dan Williams
2020-05-11 15:24 ` Vivek Goyal
2020-05-11 15:24 ` Vivek Goyal
2020-04-30 19:51 ` Dan Williams
2020-04-30 19:51 ` Dan Williams
2020-04-30 20:07 ` Andy Lutomirski
2020-04-30 20:07 ` Andy Lutomirski
2020-05-01 7:46 ` David Laight
2020-05-01 7:46 ` David Laight
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