From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrea Arcangeli <aarcange@redhat.com>,
Axel Rasmussen <axelrasmussen@google.com>,
Ives van Hoorne <ives@codesandbox.io>,
Nadav Amit <nadav.amit@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
stable@vger.kernel.org
Subject: Re: [PATCH v2 1/2] mm/migrate: Fix read-only page got writable when recover pte
Date: Tue, 15 Nov 2022 13:03:44 -0500 [thread overview]
Message-ID: <Y3PUgOUYx6ECN405@x1n> (raw)
In-Reply-To: <82d7a142-8c78-4168-37e9-7b677b18987a@redhat.com>
On Tue, Nov 15, 2022 at 06:22:03PM +0100, David Hildenbrand wrote:
> That's precisely what I had in mind recently, and I am happy to hear that
> you have similar idea:
>
> https://lkml.kernel.org/r/20221108174652.198904-6-david@redhat.com
>
> "
> Note that we don't optimize for the actual migration case:
> (1) When migration succeeds the new PTE will not be writable because the
> source PTE was not writable (protnone); in the future we
> might just optimize that case similarly by reusing
> can_change_pte_writable()/can_change_pmd_writable() when removing
> migration PTEs.
> "
I see, sorry I haven't yet read it, but sounds doable indeed.
>
> Currently, "readable_migration_entry" is even wrong: it might be PROT_NONE
> and not even readable.
Do you mean mprotect(PROT_NONE)?
If we read the "read migration entry" as "migration entry with no write
bit", it seems still fine, and code-wise after pte recovered it should
still be PROT_NONE iiuc because mk_pte() will just make a pte without
e.g. _PRESENT bit set on x86 while it'll have the _PROT_NONE bit.
May not keep true for numa balancing though: when migration happens after a
numa hint applied to a pte, it seems to me it's prone to lose the hint
after migration completes (assuming this migration is not the numa
balancing operation itself caused by a page access). Doesn't sound like a
severe issue though even if I didn't miss something, since if the page got
moved around the original hint may need to reconsider anyway.
--
Peter Xu
next prev parent reply other threads:[~2022-11-15 18:04 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-10 20:31 [PATCH v2 0/2] mm/migrate: Fix writable pte for read migration entry Peter Xu
2022-11-10 20:31 ` [PATCH v2 1/2] mm/migrate: Fix read-only page got writable when recover pte Peter Xu
2022-11-10 21:28 ` Nadav Amit
2022-11-10 22:09 ` Peter Xu
[not found] ` <CADnc5G2-7B7qyPitDY33Wb0D5a=pq-1PC=gp0f9peTtVnOvzjw@mail.gmail.com>
2022-11-10 22:08 ` Peter Xu
2022-11-10 23:42 ` Alistair Popple
2022-11-13 23:56 ` Peter Xu
2022-11-14 6:22 ` Alistair Popple
2022-11-14 16:09 ` David Hildenbrand
2022-11-14 20:09 ` Peter Xu
2022-11-15 9:13 ` David Hildenbrand
2022-11-15 16:08 ` Peter Xu
2022-11-15 17:22 ` David Hildenbrand
2022-11-15 17:54 ` David Hildenbrand
2022-11-15 18:11 ` Peter Xu
2022-11-15 18:16 ` David Hildenbrand
2022-11-15 18:03 ` Peter Xu [this message]
2022-11-15 18:08 ` David Hildenbrand
2022-11-10 20:31 ` [PATCH v2 2/2] mm/uffd: Sanity check write bit for uffd-wp protected ptes Peter Xu
2022-11-11 22:06 ` kernel test robot
2022-11-13 22:33 ` Peter Xu
2022-11-12 2:59 ` kernel test robot
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