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From: Peter Xu <peterx@redhat.com>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>,
	Jerome Glisse <jglisse@redhat.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Matthew Wilcox <willy@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Axel Rasmussen <axelrasmussen@google.com>,
	Hugh Dickins <hughd@google.com>,
	Nadav Amit <nadav.amit@gmail.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 02/23] mm: Clear vmf->pte after pte_unmap_same() returns
Date: Tue, 23 Mar 2021 11:40:53 -0400	[thread overview]
Message-ID: <20210323154053.GF6486@xz-x1> (raw)
In-Reply-To: <28c1dfdc-b72b-88a7-411c-effc078f774a@huawei.com>

On Tue, Mar 23, 2021 at 10:34:45AM +0800, Miaohe Lin wrote:
> Hi:
> On 2021/3/23 8:48, Peter Xu wrote:
> > pte_unmap_same() will always unmap the pte pointer.  After the unmap, vmf->pte
> > will not be valid any more.  We should clear it.
> > 
> > It was safe only because no one is accessing vmf->pte after pte_unmap_same()
> > returns, since the only caller of pte_unmap_same() (so far) is do_swap_page(),
> > where vmf->pte will in most cases be overwritten very soon.
> > 
> > pte_unmap_same() will be used in other places in follow up patches, so that
> > vmf->pte will not always be re-written.  This patch enables us to call
> > functions like finish_fault() because that'll conditionally unmap the pte by
> > checking vmf->pte first.  Or, alloc_set_pte() will make sure to allocate a new
> > pte even after calling pte_unmap_same().
> > 
> > Since we'll need to modify vmf->pte, directly pass in vmf into pte_unmap_same()
> > and then we can also avoid the long parameter list.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> 
> Good cleanup! Thanks.
> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>

Just a note that this is not a pure cleanup - the latter patches may start to
depend on the clearing of vmf->pte in their logic.

Thanks for the quick review!

-- 
Peter Xu


  reply	other threads:[~2021-03-23 15:41 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-23  0:48 [PATCH 00/23] userfaultfd-wp: Support shmem and hugetlbfs Peter Xu
2021-03-23  0:48 ` [PATCH 01/23] shmem/userfaultfd: Take care of UFFDIO_COPY_MODE_WP Peter Xu
2021-03-23  0:48 ` [PATCH 02/23] mm: Clear vmf->pte after pte_unmap_same() returns Peter Xu
2021-03-23  2:34   ` Miaohe Lin
2021-03-23 15:40     ` Peter Xu [this message]
2021-03-23  0:48 ` [PATCH 03/23] mm/userfaultfd: Introduce special pte for unmapped file-backed mem Peter Xu
2021-03-23  0:48 ` [PATCH 04/23] mm/swap: Introduce the idea of special swap ptes Peter Xu
2021-03-23  0:48 ` [PATCH 05/23] shmem/userfaultfd: Handle uffd-wp special pte in page fault handler Peter Xu
2021-03-23  0:48 ` [PATCH 06/23] mm: Drop first_index/last_index in zap_details Peter Xu
2021-03-23  0:48 ` [PATCH 07/23] mm: Introduce zap_details.zap_flags Peter Xu
2021-03-23  2:11   ` Matthew Wilcox
2021-03-23 15:43     ` Peter Xu
2021-03-23  0:48 ` [PATCH 08/23] mm: Introduce ZAP_FLAG_SKIP_SWAP Peter Xu
2021-03-23  0:48 ` [PATCH 09/23] mm: Pass zap_flags into unmap_mapping_pages() Peter Xu
2021-03-23  0:48 ` [PATCH 10/23] shmem/userfaultfd: Persist uffd-wp bit across zapping for file-backed Peter Xu
2021-03-23  0:49 ` [PATCH 11/23] shmem/userfaultfd: Allow wr-protect none pte for file-backed mem Peter Xu
2021-03-23  0:49 ` [PATCH 12/23] shmem/userfaultfd: Allows file-back mem to be uffd wr-protected on thps Peter Xu
2021-03-23  0:49 ` [PATCH 13/23] shmem/userfaultfd: Handle the left-overed special swap ptes Peter Xu
2021-03-23  0:49 ` [PATCH 14/23] shmem/userfaultfd: Pass over uffd-wp special swap pte when fork() Peter Xu
2021-03-23  0:49 ` [PATCH 15/23] hugetlb/userfaultfd: Hook page faults for uffd write protection Peter Xu
2021-04-21 22:02   ` Mike Kravetz
2021-03-23  0:49 ` [PATCH 16/23] hugetlb/userfaultfd: Take care of UFFDIO_COPY_MODE_WP Peter Xu
2021-04-21 23:06   ` Mike Kravetz
2021-04-22  1:14     ` Peter Xu
2021-03-23  0:49 ` [PATCH 17/23] hugetlb/userfaultfd: Handle UFFDIO_WRITEPROTECT Peter Xu
2021-04-22 18:22   ` Mike Kravetz
2021-03-23  0:49 ` [PATCH 18/23] mm/hugetlb: Introduce huge version of special swap pte helpers Peter Xu
2021-04-22 19:00   ` Mike Kravetz
2021-03-23  0:50 ` [PATCH 19/23] hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler Peter Xu
2021-04-22 22:45   ` Mike Kravetz
2021-04-26  2:08     ` Peter Xu
2021-03-23  0:50 ` [PATCH 20/23] hugetlb/userfaultfd: Allow wr-protect none ptes Peter Xu
2021-04-23  0:08   ` Mike Kravetz
2021-03-23  0:50 ` [PATCH 21/23] hugetlb/userfaultfd: Only drop uffd-wp special pte if required Peter Xu
2021-04-23 20:33   ` Mike Kravetz
2021-04-26 21:16     ` Peter Xu
2021-04-26 21:36       ` Mike Kravetz
2021-04-26 22:05         ` Peter Xu
2021-04-26 23:09           ` Mike Kravetz
2021-03-23  0:50 ` [PATCH 22/23] mm/userfaultfd: Enable write protection for shmem & hugetlbfs Peter Xu
2021-03-23  0:50 ` [PATCH 23/23] userfaultfd/selftests: Enable uffd-wp for shmem/hugetlbfs Peter Xu
2021-03-23  0:54 ` [PATCH 00/23] userfaultfd-wp: Support shmem and hugetlbfs Peter Xu
2021-04-21 16:03 ` Peter Xu
2021-04-21 21:39   ` Mike Kravetz
2021-04-22  1:16     ` Peter Xu

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