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From: Andrea Arcangeli <aarcange@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>, Linux-MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Yu Zhao <yuzhao@google.com>, Andy Lutomirski <luto@kernel.org>,
	Peter Xu <peterx@redhat.com>, Pavel Emelyanov <xemul@openvz.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Minchan Kim <minchan@kernel.org>, Will Deacon <will@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Hugh Dickins <hughd@google.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
	Kees Cook <keescook@chromium.org>,
	John Hubbard <jhubbard@nvidia.com>,
	Leon Romanovsky <leonro@nvidia.com>, Jan Kara <jack@suse.cz>,
	Kirill Tkhai <ktkhai@virtuozzo.com>
Subject: Re: [PATCH 0/2] page_count can't be used to decide when wp_page_copy
Date: Thu, 7 Jan 2021 17:02:50 -0500	[thread overview]
Message-ID: <X/eFCt/lxRKgoPXu@redhat.com> (raw)
In-Reply-To: <CAHk-=wjDkyom4haQu6OU_yykkCFqMi98qO2gUPgZBF-11krRAA@mail.gmail.com>

On Thu, Jan 07, 2021 at 01:05:19PM -0800, Linus Torvalds wrote:
> I think those would very much be worth fixing, so that if
> UFFDIO_WRITEPROTECT taking the mmapo_sem for writing causes problems,
> we can _fix_ those problems.
> 
> But I think it's entirely wrong to treat UFFDIO_WRITEPROTECT as
> specially as Andrea seems to want to treat it. Particularly with
> absolutely zero use cases to back it up.

Again for the record: there's nothing at all special in
UFFDIO_WRITEPROTECT in this respect.

If you could stop mentioning UFFDIO_WRITEPROTECT and only focus on
softdirty/clear_refs, maybe you wouldn't think my judgment is biased
towards clear_refs/softdirty too.

You can imagine the side effects of page_count doing a COW
erroneously, as corollary of the fact that KSM won't ever allow to
merge two pages if one of them is under GUP pin. Why is that?

Thanks,
Andrea


  reply	other threads:[~2021-01-07 22:04 UTC|newest]

Thread overview: 96+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-25  9:25 [RFC PATCH v2 0/2] mm: fix races due to deferred TLB flushes Nadav Amit
2020-12-25  9:25 ` [RFC PATCH v2 1/2] mm/userfaultfd: fix memory corruption due to writeprotect Nadav Amit
2021-01-04 12:22   ` Peter Zijlstra
2021-01-04 19:24     ` Andrea Arcangeli
2021-01-04 19:35       ` Nadav Amit
2021-01-04 20:19         ` Andrea Arcangeli
2021-01-04 20:39           ` Nadav Amit
2021-01-04 21:01             ` Andrea Arcangeli
2021-01-04 21:26               ` Nadav Amit
2021-01-05 18:45                 ` Andrea Arcangeli
2021-01-05 19:05                   ` Nadav Amit
2021-01-05 19:45                     ` Andrea Arcangeli
2021-01-05 20:06                       ` Nadav Amit
2021-01-05 21:06                         ` Andrea Arcangeli
2021-01-05 21:43                           ` Peter Xu
2021-01-05  8:13       ` Peter Zijlstra
2021-01-05  8:52         ` Nadav Amit
2021-01-05 14:26           ` Peter Zijlstra
2021-01-05  8:58       ` Peter Zijlstra
2021-01-05  9:22         ` Nadav Amit
2021-01-05 17:58         ` Andrea Arcangeli
2021-01-05 15:08   ` Peter Xu
2021-01-05 18:08     ` Andrea Arcangeli
2021-01-05 18:41       ` Peter Xu
2021-01-05 18:55         ` Andrea Arcangeli
2021-01-05 19:07     ` Nadav Amit
2021-01-05 19:43       ` Peter Xu
2020-12-25  9:25 ` [RFC PATCH v2 2/2] fs/task_mmu: acquire mmap_lock for write on soft-dirty cleanup Nadav Amit
2021-01-05 15:08   ` Will Deacon
2021-01-05 18:20   ` Andrea Arcangeli
2021-01-05 19:26     ` Nadav Amit
2021-01-05 20:39       ` Andrea Arcangeli
2021-01-05 21:20         ` Yu Zhao
2021-01-05 21:22         ` Nadav Amit
2021-01-05 22:16           ` Will Deacon
2021-01-06  0:29             ` Andrea Arcangeli
2021-01-06  0:02           ` Andrea Arcangeli
2021-01-07 20:04           ` [PATCH 0/2] page_count can't be used to decide when wp_page_copy Andrea Arcangeli
2021-01-07 20:04             ` [PATCH 1/2] mm: proc: Invalidate TLB after clearing soft-dirty page state Andrea Arcangeli
2021-01-07 20:04             ` [PATCH 2/2] mm: soft_dirty: userfaultfd: introduce wrprotect_tlb_flush_pending Andrea Arcangeli
2021-01-07 20:17               ` Linus Torvalds
2021-01-07 20:25                 ` Linus Torvalds
2021-01-07 20:58                 ` Andrea Arcangeli
2021-01-07 21:29                   ` Linus Torvalds
2021-01-07 21:53                     ` John Hubbard
2021-01-07 22:00                       ` Linus Torvalds
2021-01-07 22:14                         ` John Hubbard
2021-01-07 22:20                           ` Linus Torvalds
2021-01-07 22:24                             ` Linus Torvalds
2021-01-07 22:37                               ` John Hubbard
2021-01-15 11:27                       ` Jan Kara
2021-01-07 22:31                     ` Andrea Arcangeli
2021-01-07 22:42                       ` Linus Torvalds
2021-01-07 22:51                         ` Linus Torvalds
2021-01-07 23:48                           ` Andrea Arcangeli
2021-01-08  0:25                             ` Linus Torvalds
2021-01-08 12:48                               ` Will Deacon
2021-01-08 16:14                                 ` Andrea Arcangeli
2021-01-08 17:39                                   ` Linus Torvalds
2021-01-08 17:53                                     ` Andrea Arcangeli
2021-01-08 19:25                                       ` Linus Torvalds
2021-01-09  0:12                                         ` Andrea Arcangeli
2021-01-08 17:30                                 ` Linus Torvalds
2021-01-07 23:28                         ` Andrea Arcangeli
2021-01-07 21:36               ` kernel test robot
2021-01-07 20:25             ` [PATCH 0/2] page_count can't be used to decide when wp_page_copy Jason Gunthorpe
2021-01-07 20:32               ` Linus Torvalds
2021-01-07 21:05                 ` Linus Torvalds
2021-01-07 22:02                   ` Andrea Arcangeli [this message]
2021-01-07 22:17                     ` Linus Torvalds
2021-01-07 22:56                       ` Andrea Arcangeli
2021-01-09 19:32                   ` Matthew Wilcox
2021-01-09 19:46                     ` Linus Torvalds
2021-01-15 14:30                       ` Jan Kara
2021-01-07 21:54                 ` Andrea Arcangeli
2021-01-07 21:45               ` Andrea Arcangeli
2021-01-08 13:36                 ` Jason Gunthorpe
2021-01-08 17:00                   ` Andrea Arcangeli
2021-01-08 18:19                     ` Jason Gunthorpe
2021-01-08 18:31                       ` Andy Lutomirski
2021-01-08 18:38                         ` Linus Torvalds
2021-01-08 23:34                         ` Andrea Arcangeli
2021-01-09 19:03                           ` Andy Lutomirski
2021-01-09 19:15                             ` Linus Torvalds
2021-01-08 18:59                       ` Linus Torvalds
2021-01-08 22:43                       ` Andrea Arcangeli
2021-01-09  0:42                         ` Jason Gunthorpe
2021-01-09  2:50                           ` Andrea Arcangeli
2021-01-11 14:30                             ` Jason Gunthorpe
2021-01-13 21:56                           ` Jerome Glisse
2021-01-13 23:39                             ` Jason Gunthorpe
2021-01-14  2:35                               ` Jerome Glisse
     [not found]                     ` <20210109034958.6928-1-hdanton@sina.com>
2021-01-11 14:39                       ` Jason Gunthorpe
2021-01-05 21:55         ` [RFC PATCH v2 2/2] fs/task_mmu: acquire mmap_lock for write on soft-dirty cleanup Peter Xu
2021-03-02 22:13 ` [RFC PATCH v2 0/2] mm: fix races due to deferred TLB flushes Peter Xu
2021-03-02 22:14   ` Nadav Amit

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