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From: Thomas Gleixner <tglx@linutronix.de>
To: Daniel Vetter <daniel@ffwll.ch>
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Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends
Date: Sun, 20 Sep 2020 08:23:26 +0200	[thread overview]
Message-ID: <87pn6hc6g1.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <CAKMK7uENFDANQKebS_H0bhHeQRijrp1aVHQqyZPute3KBZ+fVQ@mail.gmail.com>

On Sat, Sep 19 2020 at 12:37, Daniel Vetter wrote:
> On Sat, Sep 19, 2020 at 12:35 PM Daniel Vetter <daniel@ffwll.ch> wrote:
>> I think it should be the case, but I want to double check: Will
>> copy_*_user be allowed within a kmap_temporary section? This would
>> allow us to ditch an absolute pile of slowpaths.
>
> (coffee just kicked in) copy_*_user is ofc allowed, but if you hit a
> page fault you get a short read/write. This looks like it would remove
> the need to handle these in a slowpath, since page faults can now be
> served in this new kmap_temporary sections. But this sounds too good
> to be true, so I'm wondering what I'm missing.

In principle we could allow pagefaults, but not with the currently
proposed interface which can be called from any context. Obviously if
called from atomic context it can't handle user page faults.

In theory we could make a variant which does not disable pagefaults, but
that's what kmap() already provides.

Thanks,

        tglx




  reply	other threads:[~2020-09-20  6:23 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-19  9:17 [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 01/15] mm/highmem: Un-EXPORT __kmap_atomic_idx() Thomas Gleixner
2020-09-21  6:23   ` Christoph Hellwig
2020-09-19  9:17 ` [patch RFC 02/15] highmem: Provide generic variant of kmap_atomic* Thomas Gleixner
2020-09-21  6:28   ` Christoph Hellwig
2020-09-19  9:17 ` [patch RFC 03/15] x86/mm/highmem: Use generic kmap atomic implementation Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 04/15] arc/mm/highmem: " Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 05/15] ARM: highmem: Switch to generic kmap atomic Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 06/15] csky/mm/highmem: " Thomas Gleixner
2020-09-23  0:05   ` Guo Ren
2020-09-19  9:17 ` [patch RFC 07/15] microblaze/mm/highmem: " Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 08/15] mips/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 09/15] nds32/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 10/15] powerpc/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 11/15] sparc/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 12/15] xtensa/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 13/15] mm/highmem: Remove the old kmap_atomic cruft Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 14/15] sched: highmem: Store temporary kmaps in task struct Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 15/15] mm/highmem: Provide kmap_temporary* Thomas Gleixner
2020-09-19 10:35 ` [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends Daniel Vetter
2020-09-19 10:37   ` Daniel Vetter
2020-09-20  6:23     ` Thomas Gleixner [this message]
2020-09-20  8:23       ` Daniel Vetter
2020-09-20 17:24         ` Thomas Gleixner
2020-09-19 17:18 ` Linus Torvalds
2020-09-19 17:39   ` Matthew Wilcox
2020-09-19 19:13     ` Linus Torvalds
2020-09-21 19:58     ` Ira Weiny
2020-09-20  6:41   ` Thomas Gleixner
2020-09-20  8:49     ` Thomas Gleixner
2020-09-20 16:57       ` Linus Torvalds
2020-09-20 17:40         ` Thomas Gleixner
2020-09-20 17:42           ` Linus Torvalds
2020-09-20 17:58             ` Linus Torvalds
2020-09-21  7:39             ` Thomas Gleixner
2020-09-21 16:24               ` Linus Torvalds
2020-09-21 19:27                 ` Thomas Gleixner
2020-09-23  8:40                   ` peterz
2020-09-23 13:35                     ` Thomas Gleixner
2020-09-23 15:52                     ` Steven Rostedt
2020-09-23 20:55                       ` Thomas Gleixner
2020-09-23 21:12                         ` Steven Rostedt
2020-09-24  6:57                           ` Thomas Gleixner
2020-09-24 12:32                             ` Steven Rostedt
2020-09-24 12:42                               ` Peter Zijlstra
2020-09-24 13:51                                 ` Steven Rostedt
2020-09-24 13:58                                   ` Peter Zijlstra
2020-09-24 17:55                               ` Thomas Gleixner
2020-09-24 18:58                                 ` Steven Rostedt
2020-09-24  8:27                       ` peterz
2020-09-24 19:36                         ` Daniel Bristot de Oliveira
2020-09-23 10:19                   ` peterz
2020-09-23 12:33                     ` Thomas Gleixner
2020-09-23 14:33                   ` Thomas Gleixner

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