From: David Hildenbrand <david@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-kselftest@vger.kernel.org, Shuah Khan <shuah@kernel.org>,
Hugh Dickins <hughd@google.com>, Vlastimil Babka <vbabka@suse.cz>,
Peter Xu <peterx@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
Jason Gunthorpe <jgg@nvidia.com>,
John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v1 4/7] mm/ksm: fix KSM COW breaking with userfaultfd-wp via FAULT_FLAG_UNSHARE
Date: Sat, 1 Oct 2022 10:13:41 +0200 [thread overview]
Message-ID: <e9d19ba0-2a92-02a1-3f1f-e21f65d2a3c5@redhat.com> (raw)
In-Reply-To: <20220930152742.55ee9c25b89ba483ec211be8@linux-foundation.org>
On 01.10.22 00:27, Andrew Morton wrote:
> On Fri, 30 Sep 2022 16:19:28 +0200 David Hildenbrand <david@redhat.com> wrote:
>
>> Let's stop breaking COW via a fake write fault and let's use
>> FAULT_FLAG_UNSHARE instead. This avoids any wrong side effects of the fake
>> write fault, such as mapping the PTE writable and marking the pte
>> dirty/softdirty.
>>
>> Also, this fixes KSM interaction with userfaultfd-wp: when we have a KSM
>> page that's write-protected by userfaultfd, break_ksm()->handle_mm_fault()
>> will fail with VM_FAULT_SIGBUS and will simpy return in break_ksm() with 0.
>> The warning in dmesg indicates this wrong handling:
>
> We're at -rc7. I'd prefer to avoid merging larger patchsets at this
> time.
Yes, this is 6.1 material.
>
> Is there some minimal fix for 6.0 and -stable? Or is the problem
> non-serious enough to only fix it in 6.1 and later?
>
See the end of this lengthy patch description:
"This is primarily a fix for KSM+userfaultfd-wp, however, the fake write
fault was always questionable. As this fix is not easy to backport and
it's not very critical, let's not cc stable."
This can wait, thanks!
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2022-10-01 8:13 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-30 14:19 [PATCH v1 0/7] mm/ksm: break_ksm() cleanups and fixes David Hildenbrand
2022-09-30 14:19 ` [PATCH v1 1/7] selftests/vm: add test to measure MADV_UNMERGEABLE performance David Hildenbrand
2022-10-05 20:27 ` Peter Xu
2022-09-30 14:19 ` [PATCH v1 2/7] mm/ksm: simplify break_ksm() to not rely on VM_FAULT_WRITE David Hildenbrand
2022-10-05 20:29 ` Peter Xu
2022-09-30 14:19 ` [PATCH v1 3/7] mm: remove VM_FAULT_WRITE David Hildenbrand
2022-10-05 20:29 ` Peter Xu
2022-09-30 14:19 ` [PATCH v1 4/7] mm/ksm: fix KSM COW breaking with userfaultfd-wp via FAULT_FLAG_UNSHARE David Hildenbrand
2022-09-30 22:27 ` Andrew Morton
2022-10-01 8:13 ` David Hildenbrand [this message]
2022-10-05 20:35 ` Peter Xu
2022-10-06 9:29 ` David Hildenbrand
2022-10-06 19:04 ` Peter Xu
2022-10-20 10:05 ` David Hildenbrand
2022-09-30 14:19 ` [PATCH v1 5/7] mm/pagewalk: add walk_page_range_vma() David Hildenbrand
2022-10-05 20:42 ` Peter Xu
2022-10-06 9:35 ` David Hildenbrand
2022-09-30 14:19 ` [PATCH v1 6/7] mm/ksm: convert break_ksm() to use walk_page_range_vma() David Hildenbrand
2022-10-05 21:00 ` Peter Xu
2022-10-06 9:20 ` David Hildenbrand
2022-10-06 19:28 ` Peter Xu
2022-10-21 9:11 ` David Hildenbrand
2022-10-20 8:59 ` David Hildenbrand
2022-09-30 14:19 ` [PATCH v1 7/7] mm/gup: remove FOLL_MIGRATION David Hildenbrand
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