dri-devel Archive on lore.kernel.org
 help / color / Atom feed
From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Tomasz Figa <tfiga@chromium.org>
Cc: "Jérôme Glisse" <jglisse@redhat.com>,
	linux-s390 <linux-s390@vger.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
	"Jan Kara" <jack@suse.cz>, "Pawel Osciak" <pawel@osciak.com>,
	"KVM list" <kvm@vger.kernel.org>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"DRI Development" <dri-devel@lists.freedesktop.org>,
	"Linux MM" <linux-mm@kvack.org>,
	"Kyungmin Park" <kyungmin.park@samsung.com>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"open list:DMA BUFFER SHARING FRAMEWORK"
	<linux-media@vger.kernel.org>
Subject: Re: [PATCH v4 05/15] mm/frame-vector: Use FOLL_LONGTERM
Date: Tue, 27 Oct 2020 09:05:01 +0100
Message-ID: <CAKMK7uG4f_7=9VgdQ9AE876gzLTNsszicMD9pKqeqvQybDSDpQ@mail.gmail.com> (raw)
In-Reply-To: <20201026221520.GC2802004@chromium.org>

On Mon, Oct 26, 2020 at 11:15 PM Tomasz Figa <tfiga@chromium.org> wrote:
>
> Hi Daniel,
>
> On Mon, Oct 26, 2020 at 11:58:08AM +0100, Daniel Vetter wrote:
> > This is used by media/videbuf2 for persistent dma mappings, not just
> > for a single dma operation and then freed again, so needs
> > FOLL_LONGTERM.
> >
> > Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to
> > locking issues. Rework the code to pull the pup path out from the
> > mmap_sem critical section as suggested by Jason.
> >
> > By relying entirely on the vma checks in pin_user_pages and follow_pfn
> > (for vm_flags and vma_is_fsdax) we can also streamline the code a lot.
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: Pawel Osciak <pawel@osciak.com>
> > Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> > Cc: Kyungmin Park <kyungmin.park@samsung.com>
> > Cc: Tomasz Figa <tfiga@chromium.org>
> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: John Hubbard <jhubbard@nvidia.com>
> > Cc: Jérôme Glisse <jglisse@redhat.com>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: linux-mm@kvack.org
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-samsung-soc@vger.kernel.org
> > Cc: linux-media@vger.kernel.org
> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > --
> > v2: Streamline the code and further simplify the loop checks (Jason)
> > ---
> >  mm/frame_vector.c | 50 ++++++++++++++---------------------------------
> >  1 file changed, 15 insertions(+), 35 deletions(-)
> >
>
> Thank you for the patch. Please see my comments inline.
>
> > diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> > index 10f82d5643b6..d44779e56313 100644
> > --- a/mm/frame_vector.c
> > +++ b/mm/frame_vector.c
> > @@ -38,7 +38,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> >       struct vm_area_struct *vma;
> >       int ret = 0;
> >       int err;
> > -     int locked;
> >
> >       if (nr_frames == 0)
> >               return 0;
> > @@ -48,40 +47,25 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> >
> >       start = untagged_addr(start);
> >
> > -     mmap_read_lock(mm);
> > -     locked = 1;
> > -     vma = find_vma_intersection(mm, start, start + 1);
> > -     if (!vma) {
> > -             ret = -EFAULT;
> > -             goto out;
> > -     }
> > -
> > -     /*
> > -      * While get_vaddr_frames() could be used for transient (kernel
> > -      * controlled lifetime) pinning of memory pages all current
> > -      * users establish long term (userspace controlled lifetime)
> > -      * page pinning. Treat get_vaddr_frames() like
> > -      * get_user_pages_longterm() and disallow it for filesystem-dax
> > -      * mappings.
> > -      */
> > -     if (vma_is_fsdax(vma)) {
> > -             ret = -EOPNOTSUPP;
> > -             goto out;
> > -     }
> > -
> > -     if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> > +     ret = pin_user_pages_fast(start, nr_frames,
> > +                               FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
> > +                               (struct page **)(vec->ptrs));
> > +     if (ret > 0) {
> >               vec->got_ref = true;
> >               vec->is_pfns = false;
> > -             ret = pin_user_pages_locked(start, nr_frames,
> > -                     gup_flags, (struct page **)(vec->ptrs), &locked);
>
> Should we drop the gup_flags argument, since it's ignored now?

Hm right I think an earlier version even had that, but then I moved to
inlining the functionality in all the places it's used.

I'll drop the gup flag.

> > -             goto out;
> > +             goto out_unlocked;
> >       }
> >
>
> Should we initialize ret with 0 here, since pin_user_pages_fast() can
> return a negative error code, but below we use it as a counter for the
> looked up frames?

Indeed, that's a bug. Will fix for v5.
-Daniel

> Best regards,
> Tomasz
>
> > +     mmap_read_lock(mm);
> >       vec->got_ref = false;
> >       vec->is_pfns = true;
> >       do {
> >               unsigned long *nums = frame_vector_pfns(vec);
> >
> > +             vma = find_vma_intersection(mm, start, start + 1);
> > +             if (!vma)
> > +                     break;
> > +
> >               while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
> >                       err = follow_pfn(vma, start, &nums[ret]);
> >                       if (err) {
> > @@ -92,17 +76,13 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> >                       start += PAGE_SIZE;
> >                       ret++;
> >               }
> > -             /*
> > -              * We stop if we have enough pages or if VMA doesn't completely
> > -              * cover the tail page.
> > -              */
> > -             if (ret >= nr_frames || start < vma->vm_end)
> > +             /* Bail out if VMA doesn't completely cover the tail page. */
> > +             if (start < vma->vm_end)
> >                       break;
> > -             vma = find_vma_intersection(mm, start, start + 1);
> > -     } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
> > +     } while (ret < nr_frames);
> >  out:
> > -     if (locked)
> > -             mmap_read_unlock(mm);
> > +     mmap_read_unlock(mm);
> > +out_unlocked:
> >       if (!ret)
> >               ret = -EFAULT;
> >       if (ret > 0)
> > --
> > 2.28.0
> >



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 10:58 [PATCH v4 00/15] follow_pfn and other iomap races Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 01/15] drm/exynos: Stop using frame_vector helpers Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 02/15] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 03/15] misc/habana: Stop using frame_vector helpers Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 04/15] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 05/15] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter
2020-10-26 22:15   ` Tomasz Figa
2020-10-27  8:05     ` Daniel Vetter [this message]
2020-10-26 10:58 ` [PATCH v4 06/15] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter
2020-10-26 22:03   ` Tomasz Figa
2020-10-26 10:58 ` [PATCH v4 07/15] mm: Close race in generic_access_phys Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 08/15] mm: Add unsafe_follow_pfn Daniel Vetter
     [not found]   ` <20201029085644.GA25658@infradead.org>
2020-10-29  9:23     ` Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 09/15] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter
2020-10-26 22:02   ` Tomasz Figa
2020-10-26 10:58 ` [PATCH v4 10/15] vfio/type1: Mark follow_pfn " Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 11/15] PCI: Obey iomem restrictions for procfs mmap Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 12/15] /dev/mem: Only set filp->f_mapping Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 13/15] resource: Move devmem revoke code to resource framework Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 14/15] sysfs: Support zapping of binary attr mmaps Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 15/15] PCI: Revoke mappings like devmem Daniel Vetter
     [not found] ` <20201029085749.GB25658@infradead.org>
2020-10-29  9:25   ` [PATCH v4 00/15] follow_pfn and other iomap races Daniel Vetter
     [not found]     ` <20201029092800.GA494@infradead.org>
2020-10-29  9:38       ` Daniel Vetter

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAKMK7uG4f_7=9VgdQ9AE876gzLTNsszicMD9pKqeqvQybDSDpQ@mail.gmail.com' \
    --to=daniel.vetter@ffwll.ch \
    --cc=akpm@linux-foundation.org \
    --cc=dan.j.williams@intel.com \
    --cc=daniel.vetter@intel.com \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=jack@suse.cz \
    --cc=jgg@ziepe.ca \
    --cc=jglisse@redhat.com \
    --cc=jhubbard@nvidia.com \
    --cc=kvm@vger.kernel.org \
    --cc=kyungmin.park@samsung.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-media@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-s390@vger.kernel.org \
    --cc=linux-samsung-soc@vger.kernel.org \
    --cc=m.szyprowski@samsung.com \
    --cc=mchehab@kernel.org \
    --cc=pawel@osciak.com \
    --cc=tfiga@chromium.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

dri-devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/dri-devel/0 dri-devel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dri-devel dri-devel/ https://lore.kernel.org/dri-devel \
		dri-devel@lists.freedesktop.org
	public-inbox-index dri-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.freedesktop.lists.dri-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git