From: Dan Williams <dan.j.williams@intel.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
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"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Subject: Re: [PATCH v3 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM
Date: Tue, 12 Nov 2019 15:14:58 -0800 [thread overview]
Message-ID: <CAPcyv4gUe__09cnAh3jeFogJH=sGm9U+8axRq_kCASkdbLfNbQ@mail.gmail.com> (raw)
In-Reply-To: <729a16cb-3947-c7cb-c57f-6c917d240665@nvidia.com>
On Tue, Nov 12, 2019 at 3:08 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 11/12/19 2:43 PM, Dan Williams wrote:
> ...
> > Ah, sorry. This was the first time I had looked at this series and
> > jumped in without reading the background.
> >
> > Your patch as is looks ok, I assume you've removed the FOLL_LONGTERM
> > warning in get_user_pages_remote in another patch?
> >
>
> Actually, I haven't gone quite that far. Actually this patch is the last
> change to that function. Therefore, at the end of this patchset,
> get_user_pages_remote() ends up with this check in it which
> is a less-restrictive version of the warning:
>
> /*
> * Current FOLL_LONGTERM behavior is incompatible with
> * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
> * vmas. However, this only comes up if locked is set, and there are
> * callers that do request FOLL_LONGTERM, but do not set locked. So,
> * allow what we can.
> */
> if (gup_flags & FOLL_LONGTERM) {
> if (WARN_ON_ONCE(locked))
> return -EINVAL;
> }
>
> Is that OK, or did you want to go further (possibly in a follow-up
> patchset, as I'm hoping to get this one in soon)?
That looks ok. Something to maybe push down into the core in a future
cleanup, but not something that needs to be done now.
> ...
> >>> I think check_vma_flags() should do the ((FOLL_LONGTERM | FOLL_GET) &&
> >>> vma_is_fsdax()) check and that would also remove the need for
> >>> __gup_longterm_locked.
> >>>
> >>
> >> Good idea, but there is still the call to check_and_migrate_cma_pages(),
> >> inside __gup_longterm_locked(). So it's a little more involved and
> >> we can't trivially delete __gup_longterm_locked() yet, right?
> >
> > [ add Aneesh ]
> >
> > Yes, you're right. I had overlooked that had snuck in there. That to
> > me similarly needs to be pushed down into the core with its own FOLL
> > flag, or it needs to be an explicit fixup that each caller does after
> > get_user_pages. The fact that migration silently happens as a side
> > effect of gup is too magical for my taste.
> >
>
> Yes. It's an intrusive side effect that is surprising, and not in a
> "happy surprise" way. :) . Fixing up the CMA pages by splitting that
> functionality into separate function calls sounds like an improvement
> worth exploring.
Right, future work.
next prev parent reply other threads:[~2019-11-12 23:15 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-12 0:06 [PATCH v3 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM John Hubbard
2019-11-12 0:06 ` [PATCH v3 01/23] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-11-12 0:06 ` [PATCH v3 02/23] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-12 0:06 ` [PATCH v3 03/23] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-11-12 0:06 ` [PATCH v3 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-11-12 0:06 ` [PATCH v3 05/23] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-12 0:06 ` [PATCH v3 06/23] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-11-12 0:06 ` [PATCH v3 07/23] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-12 0:06 ` [PATCH v3 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM John Hubbard
2019-11-12 20:43 ` Jason Gunthorpe
2019-11-12 22:42 ` John Hubbard
2019-11-12 22:45 ` Dan Williams
2019-11-12 23:17 ` John Hubbard
2019-11-12 23:42 ` Jason Gunthorpe
2019-11-13 0:58 ` Dan Williams
2019-11-13 1:08 ` John Hubbard
2019-11-13 1:35 ` Dan Williams
2019-11-13 2:09 ` John Hubbard
2019-11-12 21:57 ` Dan Williams
2019-11-12 22:24 ` John Hubbard
2019-11-12 22:43 ` Dan Williams
[not found] ` <729a16cb-3947-c7cb-c57f-6c917d240665@nvidia.com>
2019-11-12 23:14 ` Dan Williams [this message]
2019-11-12 0:06 ` [PATCH v3 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-12 6:51 ` Mike Rapoport
2019-11-12 0:06 ` [PATCH v3 10/23] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-12 0:06 ` [PATCH v3 11/23] IB/{core,hw,umem}: set FOLL_PIN, FOLL_LONGTERM via pin_longterm_pages*() John Hubbard
2019-11-12 20:44 ` Jason Gunthorpe
2019-11-12 21:14 ` John Hubbard
2019-11-12 0:06 ` [PATCH v3 12/23] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-12 0:06 ` [PATCH v3 13/23] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-12 0:06 ` [PATCH v3 14/23] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-12 0:06 ` [PATCH v3 15/23] net/xdp: " John Hubbard
2019-11-12 0:06 ` [PATCH v3 16/23] mm/gup: track FOLL_PIN pages John Hubbard
2019-11-12 0:06 ` [PATCH v3 17/23] media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-12 0:06 ` [PATCH v3 18/23] vfio, mm: " John Hubbard
2019-11-12 0:06 ` [PATCH v3 19/23] powerpc: book3s64: convert to pin_longterm_pages() and put_user_page() John Hubbard
2019-11-12 0:06 ` [PATCH v3 20/23] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-11-12 0:06 ` [PATCH v3 21/23] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-11-12 0:06 ` [PATCH v3 22/23] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-11-12 0:07 ` [PATCH v3 23/23] mm/gup: remove support for gup(FOLL_LONGTERM) John Hubbard
2019-11-12 20:38 ` [PATCH v3 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM Jason Gunthorpe
2019-11-12 21:10 ` John Hubbard
2019-11-13 8:22 ` Daniel Vetter
2019-11-13 9:02 ` John Hubbard
2019-11-13 10:12 ` Jan Kara
2019-11-13 11:43 ` Daniel Vetter
2019-11-13 20:28 ` John Hubbard
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