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From: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Paul Mackerras <paulus@samba.org>,
	linux-sparc <sparclinux@vger.kernel.org>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Will Deacon <will@kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	linux-s390 <linux-s390@vger.kernel.org>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Richard Weinberger <richard@nod.at>, linux-x86 <x86@kernel.org>,
	Russell King <linux@armlinux.org.uk>,
	Jason Gunthorpe <jgg@ziepe.ca>, Ingo Molnar <mingo@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Heiko Carstens <hca@linux.ibm.com>, Arnd Bergmann <arnd@arndb.de>,
	John Hubbard <jhubbard@nvidia.com>, Jeff Dike <jdike@addtoit.com>,
	linux-um <linux-um@lists.infradead.org>,
	Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arm <linux-arm-kernel@lists.infradead.org>,
	linux-mm <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-power <linuxppc-dev@lists.ozlabs.org>,
	Mike Rapoport <rppt@kernel.org>
Subject: Re: [RFC PATCH v2 1/3] mm/gup: fix gup_fast with dynamic page table folding
Date: Thu, 10 Sep 2020 21:10:10 +0200	[thread overview]
Message-ID: <20200910211010.46d064a7@thinkpad> (raw)
In-Reply-To: <CAHk-=wh3SjOE2r4WCfagL5Zq4Oj4Jsu1=1jTTi2GxGDTxP-J0Q@mail.gmail.com>

On Thu, 10 Sep 2020 11:33:17 -0700
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Thu, Sep 10, 2020 at 11:13 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > So.. To change away from the stack option I think we'd have to pass
> > the READ_ONCE value to pXX_offset() as an extra argument instead of it
> > derefing the pointer internally.
> 
> Yeah, but I think that would actually be the better model than passing
> an address to a random stack location.
> 
> It's also effectively what we do in some other places, eg the whole
> logic with "orig" in the regular pte fault handling is basically doing
> unlocked loads of the pte, various decisions on that, and then doing a
> final "is this still the same pte" after it has gotten the page table
> lock.

That sounds a lot like the pXd_offset_orig() from Martins first approach
in this thread:
https://lore.kernel.org/linuxppc-dev/20190418100218.0a4afd51@mschwideX1/

It is also the "Patch 1" option from the start of this thread:
https://lore.kernel.org/lkml/20200828140314.8556-1-gerald.schaefer@linux.ibm.com/

I guess I chose wrongly there, should have had more trust in Martins
approach, and not try so hard to do it like others...

So, maybe we can start over again, from that patch option. It would of
course also initially introduce some gup-specific helpers, like with
the other approach. It seemed harder to generalize when I thought
about it back then, but I guess it should not be a lot harder than
the _addr_end stuff.

Or, maybe this time, just not to risk Christian getting a heart attack,
we could go for the gup-specific helper first, so that we would at
least have a fix for the possible s390 data corruption. Jason, would
you agree that we send a new RFC, this time with pXd_offset_orig()
approach, and have that accepted as short-term fix?

Or would you rather also wait for some proper generic change? Have
lost that option from my radar, so cannot really judge how much more
effort it would be. I'm on vacation next week anyway, but Alexander
or Vasily (who did the option 1 patch) could look into this further.

  reply	other threads:[~2020-09-10 19:13 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-07 18:00 [RFC PATCH v2 0/3] mm/gup: fix gup_fast with dynamic page table folding Gerald Schaefer
2020-09-07 18:00 ` [RFC PATCH v2 1/3] " Gerald Schaefer
2020-09-08  5:06   ` Christophe Leroy
2020-09-08 12:09     ` Christian Borntraeger
2020-09-08 12:40       ` Christophe Leroy
2020-09-08 13:38         ` Gerald Schaefer
2020-09-08 14:30   ` Dave Hansen
2020-09-08 17:59     ` Gerald Schaefer
2020-09-09 12:29     ` Gerald Schaefer
2020-09-09 16:18       ` Dave Hansen
2020-09-09 17:25         ` Gerald Schaefer
2020-09-09 18:03           ` Jason Gunthorpe
2020-09-10  9:39             ` Alexander Gordeev
2020-09-10 13:02               ` Jason Gunthorpe
2020-09-10 13:28                 ` Gerald Schaefer
2020-09-10 15:10                   ` Jason Gunthorpe
2020-09-10 17:07                     ` Gerald Schaefer
2020-09-10 17:19                       ` Jason Gunthorpe
2020-09-10 17:57                 ` Gerald Schaefer
2020-09-10 23:21                   ` Jason Gunthorpe
2020-09-10 17:35               ` Linus Torvalds
2020-09-10 18:13                 ` Jason Gunthorpe
2020-09-10 18:33                   ` Linus Torvalds
2020-09-10 19:10                     ` Gerald Schaefer [this message]
2020-09-10 19:32                       ` Linus Torvalds
2020-09-10 21:59                         ` Jason Gunthorpe
2020-09-11  7:09                           ` peterz
2020-09-11 11:19                             ` Jason Gunthorpe
2020-09-11 19:03                             ` [PATCH] " Vasily Gorbik
2020-09-11 19:09                               ` Linus Torvalds
2020-09-11 19:40                               ` Jason Gunthorpe
2020-09-11 20:05                                 ` Jason Gunthorpe
2020-09-11 20:36                                   ` [PATCH v2] " Vasily Gorbik
2020-09-15 17:09                                     ` Vasily Gorbik
2020-09-15 17:14                                     ` Jason Gunthorpe
2020-09-15 17:18                                     ` Mike Rapoport
2020-09-15 17:31                                     ` John Hubbard
2020-09-10 21:22                   ` [RFC PATCH v2 1/3] " John Hubbard
2020-09-10 22:11                     ` Jason Gunthorpe
2020-09-10 22:17                       ` John Hubbard
2020-09-11 12:19                       ` Alexander Gordeev
2020-09-11 16:45                         ` Linus Torvalds
2020-09-10 13:11             ` Gerald Schaefer
2020-09-07 18:00 ` [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions page-table entry aware Gerald Schaefer
2020-09-08  5:14   ` Christophe Leroy
2020-09-08  7:46     ` Alexander Gordeev
2020-09-08  8:16       ` Christophe Leroy
2020-09-08 14:15         ` Alexander Gordeev
2020-09-09  8:38           ` Christophe Leroy
2020-09-08 14:25     ` Alexander Gordeev
2020-09-08 13:26   ` Jason Gunthorpe
2020-09-08 14:33   ` Dave Hansen
2020-09-07 18:00 ` [RFC PATCH v2 3/3] mm: make generic pXd_addr_end() macros inline functions Gerald Schaefer
2020-09-07 20:15   ` Mike Rapoport
2020-09-08  5:19   ` Christophe Leroy
2020-09-08 15:48     ` Alexander Gordeev
2020-09-08 17:20       ` Christophe Leroy
2020-09-07 20:12 ` [RFC PATCH v2 0/3] mm/gup: fix gup_fast with dynamic page table folding Mike Rapoport
2020-09-08  5:22   ` Christophe Leroy
2020-09-08 17:36     ` Gerald Schaefer
2020-09-09 16:12       ` Gerald Schaefer
2020-09-08  4:42 ` Christophe Leroy

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