From: David Hildenbrand <david@redhat.com>
To: Peter Xu <peterx@redhat.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
Matthew Wilcox <willy@infradead.org>,
Olivier Dion <odion@efficios.com>,
linux-mm@kvack.org
Subject: Re: [RFC PATCH 0/2] SKSM: Synchronous Kernel Samepage Merging
Date: Mon, 3 Mar 2025 17:36:25 +0100 [thread overview]
Message-ID: <c35cf981-3530-4496-8400-912f230cfd06@redhat.com> (raw)
In-Reply-To: <Z8XEZsZ2LZfqwfhu@x1.local>
On 03.03.25 16:01, Peter Xu wrote:
> On Sat, Mar 01, 2025 at 10:44:22AM -0500, Mathieu Desnoyers wrote:
>>>> Also, I notice that do_wp_page() only calls handle_userfault
>>>> VM_UFFD_WP when vm_fault flags does not have FAULT_FLAG_UNSHARE
>>>> set.
>>>
>>> AFAICT that's expected, unshare should only be set on reads, never writes.
>>> So uffd-wp shouldn't trap any of those.
>>
>> I'm confused by your comment. I thought unshare only applies to
>> *write* faults. What am I missing ?
>
> The major path so far to set unshare is here in GUP (ignoring two corner
> cases used in either s390 and ksm):
"unshare" fault, in contrast to a write fault, will not turn the PTE
writable.
That's why it does not trigger userfaultfd-wp: there is no write access,
write-protection is left unchanged.
--
Cheers,
David / dhildenb
next prev parent reply other threads:[~2025-03-03 16:36 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-28 2:30 Mathieu Desnoyers
2025-02-28 2:30 ` [RFC PATCH 1/2] mm: Introduce " Mathieu Desnoyers
2025-02-28 2:30 ` [RFC PATCH 2/2] selftests/kskm: Introduce SKSM basic test Mathieu Desnoyers
2025-02-28 2:51 ` [RFC PATCH 0/2] SKSM: Synchronous Kernel Samepage Merging Linus Torvalds
2025-02-28 3:03 ` Mathieu Desnoyers
2025-02-28 5:17 ` Linus Torvalds
2025-02-28 13:59 ` David Hildenbrand
2025-02-28 14:59 ` Sean Christopherson
2025-02-28 15:10 ` David Hildenbrand
2025-02-28 15:19 ` David Hildenbrand
2025-02-28 21:38 ` Mathieu Desnoyers
2025-02-28 21:45 ` David Hildenbrand
2025-02-28 21:49 ` Mathieu Desnoyers
2025-02-28 15:01 ` Mathieu Desnoyers
2025-02-28 15:18 ` David Hildenbrand
2025-02-28 14:59 ` Mathieu Desnoyers
2025-02-28 16:32 ` Peter Xu
2025-02-28 17:53 ` Mathieu Desnoyers
2025-02-28 22:32 ` Peter Xu
2025-03-01 15:44 ` Mathieu Desnoyers
2025-03-03 15:01 ` Peter Xu
2025-03-03 16:36 ` David Hildenbrand [this message]
2025-03-03 20:01 ` Mathieu Desnoyers
2025-03-03 20:45 ` Peter Xu
2025-03-03 20:49 ` David Hildenbrand
2025-03-05 14:06 ` Mathieu Desnoyers
2025-03-05 19:22 ` David Hildenbrand
2025-02-28 15:34 ` David Hildenbrand
2025-02-28 15:38 ` Matthew Wilcox
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