From: John Hubbard <jhubbard@nvidia.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>, Yu Zhao <yuzhao@google.com>
Cc: "Peter Zijlstra" <peterz@infradead.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Michal Hocko" <mhocko@suse.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Arnaldo Carvalho de Melo" <acme@kernel.org>,
"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
"Jiri Olsa" <jolsa@redhat.com>,
"Namhyung Kim" <namhyung@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Hugh Dickins" <hughd@google.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
"David Rientjes" <rientjes@google.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Lance Roy" <ldr709@gmail.com>,
"Ralph Campbell" <rcampbell@nvidia.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Dave Airlie" <airlied@redhat.com>,
"Thomas Hellstrom" <thellstrom@vmware.com>,
"Souptick Joarder" <jrdr.linux@gmail.com>,
"Mel Gorman" <mgorman@suse.de>, "Jan Kara" <jack@suse.cz>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Huang Ying" <ying.huang@intel.com>,
"Aaron Lu" <ziqian.lzq@antfin.com>,
"Omar Sandoval" <osandov@fb.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Vineeth Remanan Pillai" <vpillai@digitalocean.com>,
"Daniel Jordan" <daniel.m.jordan@oracle.com>,
"Mike Rapoport" <rppt@linux.ibm.com>,
"Joel Fernandes" <joel@joelfernandes.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"Alexander Duyck" <alexander.h.duyck@linux.intel.com>,
"Pavel Tatashin" <pavel.tatashin@microsoft.com>,
"David Hildenbrand" <david@redhat.com>,
"Juergen Gross" <jgross@suse.com>,
"Anthony Yznaga" <anthony.yznaga@oracle.com>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 3/4] mm: don't expose non-hugetlb page to fast gup prematurely
Date: Thu, 26 Sep 2019 20:26:46 -0700 [thread overview]
Message-ID: <9465df76-0229-1b44-5646-5cced1bc1718@nvidia.com> (raw)
In-Reply-To: <20190926102036.od2wamdx2s7uznvq@box>
On 9/26/19 3:20 AM, Kirill A. Shutemov wrote:
> On Wed, Sep 25, 2019 at 04:26:54PM -0600, Yu Zhao wrote:
>> On Wed, Sep 25, 2019 at 10:25:30AM +0200, Peter Zijlstra wrote:
>>> On Tue, Sep 24, 2019 at 05:24:58PM -0600, Yu Zhao wrote:
...
>>> I'm thinking this patch make stuff rather fragile.. Should we instead
>>> stick the barrier in set_p*d_at() instead? Or rather, make that store a
>>> store-release?
>>
>> I prefer it this way too, but I suspected the majority would be
>> concerned with the performance implications, especially those
>> looping set_pte_at()s in mm/huge_memory.c.
>
> We can rename current set_pte_at() to __set_pte_at() or something and
> leave it in places where barrier is not needed. The new set_pte_at()( will
> be used in the rest of the places with the barrier inside.
+1, sounds nice. I was unhappy about the wide-ranging changes that would have
to be maintained. So this seems much better.
>
> BTW, have you looked at other levels of page table hierarchy. Do we have
> the same issue for PMD/PUD/... pages?
>
Along the lines of "what other memory barriers might be missing for
get_user_pages_fast(), I'm also concerned that the synchronization between
get_user_pages_fast() and freeing the page tables might be technically broken,
due to missing memory barriers on the get_user_pages_fast() side. Details:
gup_fast() disables interrupts, but I think it also needs some sort of
memory barrier(s), in order to prevent reads of the page table (gup_pgd_range,
etc) from speculatively happening before the interrupts are disabled.
Leonardo Bras's recent patchset brought this to my attention. Here, he's
recommending adding atomic counting inc/dec before and after the gup_fast()
irq disable/enable points:
https://lore.kernel.org/r/20190920195047.7703-4-leonardo@linux.ibm.com
...and that lead to noticing a general lack of barriers there.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2019-09-27 3:26 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-08 22:56 [PATCH] mm: don't expose page to fast gup before it's ready Yu Zhao
2018-01-09 8:46 ` Michal Hocko
2018-01-09 10:10 ` Yu Zhao
2018-01-31 23:07 ` Andrew Morton
2019-05-14 21:25 ` Andrew Morton
2019-05-14 23:07 ` Yu Zhao
2019-09-14 7:05 ` [PATCH v2] mm: don't expose page to fast gup prematurely Yu Zhao
2019-09-24 11:23 ` Kirill A. Shutemov
2019-09-24 22:05 ` Yu Zhao
2019-09-25 12:17 ` Kirill A. Shutemov
2019-09-26 3:58 ` Yu Zhao
2019-09-24 23:24 ` [PATCH v3 1/4] mm: remove unnecessary smp_wmb() in collapse_huge_page() Yu Zhao
2019-09-24 23:24 ` [PATCH v3 2/4] mm: don't expose hugetlb page to fast gup prematurely Yu Zhao
2019-09-24 23:24 ` [PATCH v3 3/4] mm: don't expose non-hugetlb " Yu Zhao
2019-09-25 8:25 ` Peter Zijlstra
2019-09-25 22:26 ` Yu Zhao
2019-09-26 10:20 ` Kirill A. Shutemov
2019-09-27 3:26 ` John Hubbard [this message]
2019-09-27 5:06 ` Yu Zhao
2019-10-01 22:31 ` John Hubbard
2019-10-02 0:00 ` Yu Zhao
2019-09-27 12:33 ` Michal Hocko
2019-09-27 18:31 ` Yu Zhao
2019-09-27 19:31 ` John Hubbard
2019-09-29 22:47 ` John Hubbard
2019-09-30 9:20 ` Jan Kara
2019-09-30 17:57 ` John Hubbard
2019-10-01 7:10 ` Jan Kara
2019-10-01 8:36 ` Peter Zijlstra
2019-10-01 8:40 ` Jan Kara
2019-10-01 18:43 ` John Hubbard
2019-10-02 9:24 ` Jan Kara
2019-10-02 17:33 ` John Hubbard
2019-09-24 23:24 ` [PATCH v3 4/4] mm: remove unnecessary smp_wmb() in __SetPageUptodate() Yu Zhao
2019-09-24 23:50 ` Matthew Wilcox
2019-09-25 22:03 ` Yu Zhao
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