From: Jason Gunthorpe <jgg@nvidia.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
David Rientjes <rientjes@google.com>,
Shakeel Butt <shakeelb@google.com>,
John Hubbard <jhubbard@nvidia.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Yang Shi <shy828301@gmail.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Matthew Wilcox <willy@infradead.org>,
Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
Michal Hocko <mhocko@kernel.org>, Nadav Amit <namit@vmware.com>,
Rik van Riel <riel@surriel.com>, Roman Gushchin <guro@fb.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Peter Xu <peterx@redhat.com>, Donald Dutile <ddutile@redhat.com>,
Christoph Hellwig <hch@lst.de>, Oleg Nesterov <oleg@redhat.com>,
Jan Kara <jack@suse.cz>, Liang Zhang <zhangliang5@huawei.com>,
Pedro Gomes <pedrodemargomes@gmail.com>,
Oded Gabbay <oded.gabbay@gmail.com>,
linux-mm@kvack.org
Subject: Re: [PATCH RFC 12/13] mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page
Date: Wed, 2 Mar 2022 16:59:34 -0400 [thread overview]
Message-ID: <20220302205934.GV219866@nvidia.com> (raw)
In-Reply-To: <fb895ba3-9d7e-7421-d5c6-f5e7a2d1231a@redhat.com>
On Wed, Mar 02, 2022 at 09:38:09PM +0100, David Hildenbrand wrote:
> (a) I want a R/O pin to observe file modifications.
> (b) I want the R/O pin to *not* observe file modifications but observe
> my (eventual? if any) private modifications,
A scenario I know that motivated this is fairly straightfoward:
static char data[] = {};
ibv_reg_mr(data, READ_ONLY)
data[0] = 1
.. go touch data via DMA ..
We want to reliably observe the '1'
What is happening under the covers is that 'data' is placed in the
.data segment and becomes a file backed MAP_PRIVATE page. The write
COWs that page
It would work OK if it was in .bss instead
I think the FOLL_FORCE is there because otherwise the trick doesn't
work on true RO pages and the API becomes broken.
Jason
next prev parent reply other threads:[~2022-03-02 20:59 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-24 12:26 [PATCH RFC 00/13] mm: COW fixes part 2: reliable GUP pins of anonymous pages David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 01/13] mm/rmap: fix missing swap_free() in try_to_unmap() after arch_unmap_one() failed David Hildenbrand
2022-02-24 16:26 ` Khalid Aziz
2022-02-24 12:26 ` [PATCH RFC 02/13] mm/hugetlb: take src_mm->write_protect_seq in copy_hugetlb_page_range() David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 03/13] mm/memory: slightly simplify copy_present_pte() David Hildenbrand
2022-02-25 5:15 ` Hillf Danton
2022-02-25 8:01 ` David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 04/13] mm/rmap: split page_dup_rmap() into page_dup_file_rmap() and page_try_dup_anon_rmap() David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 05/13] mm/rmap: remove do_page_add_anon_rmap() David Hildenbrand
2022-02-24 17:29 ` Linus Torvalds
2022-02-24 17:41 ` David Hildenbrand
2022-02-24 17:48 ` Linus Torvalds
2022-02-25 9:01 ` David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 06/13] mm/rmap: pass rmap flags to hugepage_add_anon_rmap() David Hildenbrand
2022-02-24 17:37 ` Linus Torvalds
2022-02-24 12:26 ` [PATCH RFC 07/13] mm/rmap: use page_move_anon_rmap() when reusing a mapped PageAnon() page exclusively David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 08/13] mm/page-flags: reuse PG_slab as PG_anon_exclusive for PageAnon() pages David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 09/13] mm: remember exclusively mapped anonymous pages with PG_anon_exclusive David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 10/13] mm/gup: disallow follow_page(FOLL_PIN) David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 11/13] mm: support GUP-triggered unsharing of anonymous pages David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 12/13] mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page David Hildenbrand
2022-03-02 16:55 ` Jason Gunthorpe
2022-03-02 20:38 ` David Hildenbrand
2022-03-02 20:59 ` Jason Gunthorpe [this message]
2022-03-03 8:07 ` David Hildenbrand
2022-03-03 1:47 ` John Hubbard
2022-03-03 8:06 ` David Hildenbrand
2022-03-09 7:37 ` David Hildenbrand
2022-02-24 12:26 ` [PATCH RFC 13/13] mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning David Hildenbrand
2022-03-01 8:24 ` [PATCH RFC 00/13] mm: COW fixes part 2: reliable GUP pins of anonymous pages David Hildenbrand
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