From: Jason Gunthorpe <jgg@nvidia.com>
To: David Hildenbrand <david@redhat.com>
Cc: "Kasireddy, Vivek" <vivek.kasireddy@intel.com>,
"Kim, Dongwon" <dongwon.kim@intel.com>,
"Chang, Junxiao" <junxiao.chang@intel.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
Alistair Popple <apopple@nvidia.com>,
Hugh Dickins <hughd@google.com>, Peter Xu <peterx@redhat.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Gerd Hoffmann <kraxel@redhat.com>,
Mike Kravetz <mike.kravetz@oracle.com>
Subject: Re: [RFC v1 1/3] mm/mmu_notifier: Add a new notifier for mapping updates (new pages)
Date: Tue, 1 Aug 2023 09:26:35 -0300 [thread overview]
Message-ID: <ZMj5+7sgkPqHT5Vt@nvidia.com> (raw)
In-Reply-To: <48f22686-2c1b-fd9d-91ba-da6105d410db@redhat.com>
On Tue, Aug 01, 2023 at 02:26:03PM +0200, David Hildenbrand wrote:
> On 01.08.23 14:23, Jason Gunthorpe wrote:
> > On Tue, Aug 01, 2023 at 02:22:12PM +0200, David Hildenbrand wrote:
> > > On 01.08.23 14:19, Jason Gunthorpe wrote:
> > > > On Tue, Aug 01, 2023 at 05:32:38AM +0000, Kasireddy, Vivek wrote:
> > > >
> > > > > > You get another invalidate because the memfd removes the zero pages
> > > > > > that hmm_range_fault installed in the PTEs before replacing them with
> > > > > > actual writable pages. Then you do the move, and another
> > > > > > hmm_range_fault, and basically the whole thing over again. Except this
> > > > > > time instead of returning zero pages it returns actual writable
> > > > > > page.
> > > >
> > > > > Ok, when I tested earlier (by registering an invalidate callback) but without
> > > > > hmm_range_fault(), I did not find this additional invalidate getting triggered.
> > > > > Let me try with hmm_range_fault() and see if everything works as expected.
> > > > > Thank you for your help.
> > > >
> > > > If you do not get an invalidate then there is a pretty serious bug in
> > > > the mm that needs fixing.
> > > >
> > > > Anything hmm_range_fault() returns must be invalidated if the
> > > > underying CPU mapping changes for any reasons. Since hmm_range_fault()
> > > > will populate zero pages when reading from a hole in a memfd, it must
> > > > also get an invalidation when the zero pages are changed into writable
> > > > pages.
> > >
> > > Can you point me at the code that returns that (shared) zero page?
> >
> > It calls handle_mm_fault() - shouldn't that do it? Same as if the CPU
> > read faulted the page?
>
> To the best of my knowledge, the shared zeropage is only used in
> MAP_PRIVATE|MAP_AON mappings and in weird DAX mappings.
>
> If that changed, we have to fix FOLL_PIN|FOLL_LONGTERM for MAP_SHARED VMAs.
>
> If you read-fault on a memfd hole, you should get a proper "zeroed"
> pagecache page that effectively "filled that hole" -- so there is no file
> hole anymore.
Sounds fine then :)
Jason
next prev parent reply other threads:[~2023-08-01 12:26 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-18 8:28 [RFC v1 0/3] udmabuf: Replace pages when there is FALLOC_FL_PUNCH_HOLE in memfd Vivek Kasireddy
2023-07-18 8:28 ` [RFC v1 1/3] mm/mmu_notifier: Add a new notifier for mapping updates (new pages) Vivek Kasireddy
2023-07-18 15:36 ` Jason Gunthorpe
2023-07-19 0:05 ` Kasireddy, Vivek
2023-07-19 0:24 ` Jason Gunthorpe
2023-07-19 6:19 ` Kasireddy, Vivek
2023-07-19 2:08 ` Alistair Popple
2023-07-20 7:43 ` Kasireddy, Vivek
2023-07-20 9:00 ` Alistair Popple
2023-07-24 7:54 ` Kasireddy, Vivek
2023-07-24 13:35 ` Jason Gunthorpe
2023-07-24 20:32 ` Kasireddy, Vivek
2023-07-25 4:30 ` Hugh Dickins
2023-07-25 22:24 ` Kasireddy, Vivek
2023-07-27 21:43 ` Peter Xu
2023-07-29 0:08 ` Kasireddy, Vivek
2023-07-31 17:05 ` Peter Xu
2023-08-01 7:11 ` Kasireddy, Vivek
2023-08-01 21:57 ` Peter Xu
2023-08-03 8:08 ` Kasireddy, Vivek
2023-08-03 13:02 ` Peter Xu
2023-07-25 12:36 ` Jason Gunthorpe
2023-07-25 22:44 ` Kasireddy, Vivek
2023-07-25 22:53 ` Jason Gunthorpe
2023-07-27 7:34 ` Kasireddy, Vivek
2023-07-27 11:58 ` Jason Gunthorpe
2023-07-29 0:46 ` Kasireddy, Vivek
2023-07-30 23:09 ` Jason Gunthorpe
2023-08-01 5:32 ` Kasireddy, Vivek
2023-08-01 12:19 ` Jason Gunthorpe
2023-08-01 12:22 ` David Hildenbrand
2023-08-01 12:23 ` Jason Gunthorpe
2023-08-01 12:26 ` David Hildenbrand
2023-08-01 12:26 ` Jason Gunthorpe [this message]
2023-08-01 12:28 ` David Hildenbrand
2023-08-01 17:53 ` Kasireddy, Vivek
2023-08-01 18:19 ` Jason Gunthorpe
2023-08-03 7:35 ` Kasireddy, Vivek
2023-08-03 12:14 ` Jason Gunthorpe
2023-08-03 12:32 ` David Hildenbrand
2023-08-04 0:14 ` Alistair Popple
2023-08-04 6:39 ` Kasireddy, Vivek
2023-08-04 7:23 ` David Hildenbrand
2023-08-04 21:53 ` Kasireddy, Vivek
2023-08-04 12:49 ` Jason Gunthorpe
2023-08-08 7:37 ` Kasireddy, Vivek
2023-08-08 12:42 ` Jason Gunthorpe
2023-08-16 6:43 ` Kasireddy, Vivek
2023-08-21 9:02 ` Alistair Popple
2023-08-22 6:14 ` Kasireddy, Vivek
2023-08-22 8:15 ` Alistair Popple
2023-08-24 6:48 ` Kasireddy, Vivek
2023-08-28 4:38 ` Kasireddy, Vivek
2023-08-30 16:02 ` Jason Gunthorpe
2023-07-25 3:38 ` Alistair Popple
2023-07-24 13:36 ` Alistair Popple
2023-07-24 13:37 ` Jason Gunthorpe
2023-07-24 20:42 ` Kasireddy, Vivek
2023-07-25 3:14 ` Alistair Popple
2023-07-18 8:28 ` [RFC v1 2/3] udmabuf: Replace pages when there is FALLOC_FL_PUNCH_HOLE in memfd Vivek Kasireddy
2023-08-02 12:40 ` Daniel Vetter
2023-08-03 8:24 ` Kasireddy, Vivek
2023-08-03 8:32 ` Daniel Vetter
2023-07-18 8:28 ` [RFC v1 3/3] selftests/dma-buf/udmabuf: Add tests for huge pages and FALLOC_FL_PUNCH_HOLE Vivek Kasireddy
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