From: Linus Torvalds <torvalds@linux-foundation.org>
To: David Hildenbrand <david@redhat.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
David Rientjes <rientjes@google.com>,
Shakeel Butt <shakeelb@google.com>,
John Hubbard <jhubbard@nvidia.com>,
Jason Gunthorpe <jgg@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>, Linux-MM <linux-mm@kvack.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb)
Date: Fri, 17 Dec 2021 12:43:42 -0800 [thread overview]
Message-ID: <CAHk-=wge4Pcrhg-uCyCRVaUBb5B4NdSxb3TNhB5pnnqDqw6Ztg@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wgD1Y_hV3eCRL55m+sGfmwic0wbq+0LV8youYKirHJTog@mail.gmail.com>
On Fri, Dec 17, 2021 at 12:39 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> At the time of such a shared pin, you can do what we already do:
> re-use the page if it has a refcount of 1. Or do an early COW event
> (feel free to avoid the "mark it writable and dirty").
Note that this also depends on fork() doing the right thing, marking
things for "a fork() can not share this page any more".
Which it does for regular pages, and is exactly what that
page_needs_cow_for_dma() logic is all about (and the special
write_protect_seq around gup/fork).
I do believe that huge-pages don't do it right. But I think that as
you try to fix hugepages, you are now breaking the normal case.
If all your logic was only about hugepages, I wouldn't care so much.
But you are playing questionable games with code that I think is
correct.
Please explain why.
Linus
next prev parent reply other threads:[~2021-12-17 20:44 UTC|newest]
Thread overview: 127+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-17 11:30 [PATCH v1 00/11] mm: COW fixes part 1: fix the COW security issue for THP and hugetlb David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 01/11] seqlock: provide lockdep-free raw_seqcount_t variant David Hildenbrand
2021-12-17 17:02 ` Nadav Amit
2021-12-17 17:29 ` David Hildenbrand
2021-12-17 17:49 ` David Hildenbrand
2021-12-17 18:01 ` Nadav Amit
2021-12-17 21:28 ` Thomas Gleixner
2021-12-17 22:02 ` David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 02/11] mm: thp: consolidate mapcount logic on THP split David Hildenbrand
2021-12-17 19:06 ` Yang Shi
2021-12-18 14:24 ` Kirill A. Shutemov
2021-12-17 11:30 ` [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page_mapcount() David Hildenbrand
2021-12-17 17:16 ` Nadav Amit
2021-12-17 17:30 ` David Hildenbrand
2021-12-17 18:06 ` Mike Kravetz
2021-12-17 18:11 ` David Hildenbrand
2021-12-17 19:07 ` Yang Shi
2021-12-18 14:31 ` Kirill A. Shutemov
2021-12-17 11:30 ` [PATCH v1 04/11] mm: thp: simlify total_mapcount() David Hildenbrand
2021-12-17 19:12 ` Yang Shi
2021-12-18 14:35 ` Kirill A. Shutemov
2021-12-17 11:30 ` [PATCH v1 05/11] mm: thp: allow for reading the THP mapcount atomically via a raw_seqlock_t David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb) David Hildenbrand
2021-12-17 19:04 ` Linus Torvalds
2021-12-17 19:22 ` Linus Torvalds
2021-12-17 20:17 ` David Hildenbrand
2021-12-17 20:36 ` Linus Torvalds
2021-12-17 20:39 ` Linus Torvalds
2021-12-17 20:43 ` Linus Torvalds [this message]
2021-12-17 20:42 ` David Hildenbrand
2021-12-17 20:45 ` Linus Torvalds
2021-12-18 22:52 ` Kirill A. Shutemov
2021-12-18 23:05 ` Linus Torvalds
2021-12-17 20:47 ` Jason Gunthorpe
2021-12-17 20:56 ` Linus Torvalds
2021-12-17 21:17 ` David Hildenbrand
2021-12-17 21:04 ` David Hildenbrand
2021-12-18 0:50 ` Jason Gunthorpe
2021-12-17 21:15 ` Nadav Amit
2021-12-17 21:20 ` David Hildenbrand
2021-12-18 0:50 ` Jason Gunthorpe
2021-12-18 1:53 ` Linus Torvalds
2021-12-18 2:17 ` Linus Torvalds
2021-12-18 2:42 ` Linus Torvalds
2021-12-18 3:36 ` Linus Torvalds
2021-12-18 3:05 ` Jason Gunthorpe
2021-12-18 3:30 ` Nadav Amit
2021-12-18 3:38 ` Linus Torvalds
2021-12-18 18:42 ` Jason Gunthorpe
2021-12-18 21:48 ` Nadav Amit
2021-12-18 22:53 ` Linus Torvalds
2021-12-19 0:19 ` Nadav Amit
2021-12-19 0:35 ` Linus Torvalds
2021-12-19 6:02 ` Nadav Amit
2021-12-19 8:01 ` John Hubbard
2021-12-19 11:30 ` Matthew Wilcox
2021-12-19 17:27 ` Linus Torvalds
2021-12-19 17:44 ` David Hildenbrand
2021-12-19 17:44 ` Linus Torvalds
2021-12-19 17:59 ` David Hildenbrand
2021-12-19 21:12 ` Matthew Wilcox
2021-12-19 21:27 ` Linus Torvalds
2021-12-19 21:47 ` Matthew Wilcox
2021-12-19 21:53 ` Linus Torvalds
2021-12-19 22:02 ` Matthew Wilcox
2021-12-19 22:12 ` Linus Torvalds
2021-12-19 22:26 ` Matthew Wilcox
2021-12-20 18:37 ` Matthew Wilcox
2021-12-20 18:52 ` Matthew Wilcox
2021-12-20 19:38 ` Linus Torvalds
2021-12-20 19:15 ` Linus Torvalds
2021-12-20 21:02 ` Matthew Wilcox
2021-12-20 21:27 ` Linus Torvalds
2021-12-21 1:03 ` Jason Gunthorpe
2021-12-21 3:29 ` Matthew Wilcox
2021-12-21 8:58 ` David Hildenbrand
2021-12-21 14:28 ` Jason Gunthorpe
[not found] ` <303f21d3-42b4-2f11-3f22-28f89f819080@redhat.com>
2021-12-21 23:54 ` Jason Gunthorpe
2021-12-21 17:05 ` Linus Torvalds
2021-12-21 17:40 ` David Hildenbrand
2021-12-21 18:00 ` Linus Torvalds
[not found] ` <dda021c8-69ec-c660-46be-793ae345a5bb@redhat.com>
2021-12-21 21:11 ` John Hubbard
2021-12-21 18:07 ` Jan Kara
2021-12-21 18:30 ` Linus Torvalds
[not found] ` <d23ede12-5df7-2f28-00fd-ea58d85ae400@redhat.com>
2021-12-21 18:58 ` Linus Torvalds
2021-12-21 21:16 ` John Hubbard
2021-12-21 19:07 ` Jason Gunthorpe
[not found] ` <3e0868e6-c714-1bf8-163f-389989bf5189@redhat.com>
[not found] ` <dfe1c8d5-6fac-9040-0272-6d77bafa6a16@redhat.com>
2021-12-22 12:41 ` Jan Kara
[not found] ` <4a28e8a0-2efa-8b5e-10b5-38f1fc143a98@redhat.com>
2021-12-22 14:42 ` Jan Kara
[not found] ` <505d3d0f-23ee-0eec-0571-8058b8eedb97@redhat.com>
2021-12-22 16:08 ` Jan Kara
2021-12-22 16:44 ` Matthew Wilcox
2021-12-22 18:40 ` Linus Torvalds
2021-12-23 12:54 ` Jan Kara
2021-12-23 17:18 ` Linus Torvalds
2021-12-23 0:21 ` Matthew Wilcox
2021-12-24 2:53 ` Jason Gunthorpe
2021-12-24 4:53 ` Matthew Wilcox
2022-01-04 0:33 ` Jason Gunthorpe
2021-12-21 23:59 ` Jason Gunthorpe
2021-12-22 12:44 ` Jan Kara
2021-12-17 20:45 ` David Hildenbrand
2021-12-17 20:51 ` Linus Torvalds
2021-12-17 20:55 ` David Hildenbrand
2021-12-17 21:36 ` Linus Torvalds
2021-12-17 21:47 ` David Hildenbrand
2021-12-17 21:50 ` Linus Torvalds
2021-12-17 22:29 ` David Hildenbrand
2021-12-17 22:58 ` Linus Torvalds
2021-12-17 23:29 ` David Hildenbrand
2021-12-17 23:53 ` Nadav Amit
2021-12-18 4:02 ` Linus Torvalds
2021-12-18 4:52 ` Nadav Amit
2021-12-18 5:03 ` Matthew Wilcox
2021-12-18 5:23 ` Nadav Amit
2021-12-18 18:37 ` Linus Torvalds
2021-12-17 22:18 ` Linus Torvalds
2021-12-17 22:43 ` David Hildenbrand
2021-12-17 23:20 ` Linus Torvalds
2021-12-18 9:57 ` David Hildenbrand
2021-12-18 19:21 ` Linus Torvalds
2021-12-18 19:52 ` Linus Torvalds
2021-12-19 8:43 ` David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 07/11] mm: gup: trigger unsharing via FAULT_FLAG_UNSHARE when required (!hugetlb) David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 08/11] mm: hugetlb: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 09/11] mm: gup: trigger unsharing via FAULT_FLAG_UNSHARE when required (hugetlb) David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 10/11] mm: thp: introduce and use page_trans_huge_anon_shared() David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 11/11] selftests/vm: add tests for the known COW security issues David Hildenbrand
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