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From: Andrew Morton <akpm@linux-foundation.org>
To: David Hildenbrand <david@redhat.com>
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: Fri, 30 Sep 2022 15:27:42 -0700	[thread overview]
Message-ID: <20220930152742.55ee9c25b89ba483ec211be8@linux-foundation.org> (raw)
In-Reply-To: <20220930141931.174362-5-david@redhat.com>

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.

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?

  reply	other threads:[~2022-09-30 22:28 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 [this message]
2022-10-01  8:13     ` David Hildenbrand
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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