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AJvYcCX5wHZwLOolEbzn/mB4wUhNrPOenZJkw1cyviuIzdUYP/uxhuiL0q8wr6NwhkxOtytFzf/2a8/bHw==@kvack.org X-Gm-Message-State: AOJu0YzJqpKIV53fp0RNWestiXyTyQqAaWkIGRT61pFN/9wtWK3Evf94 4xOf/H2q97viWwVS7Xxw2wN4VIVQ3WTji90qWyyDGX+BlE+ot+dip/tUNDROC46V03Gyf7iI+sc Mu8WmV5lsoO7YhtnNKYoiLqZNb48= X-Gm-Gg: ASbGncv50FVLfjSMpbZJHiHSfitBtA5ZISHdAt/g6gE9vByuOBxR3cfRhjl/JQScmuq uX48Owqq1yEU1now0D0D+CL2MQ7kmrWn+tGz6izgHPYh0WsNhjftkIrw0vUh9o8nEkeaeqOep87 eniqA8d1+fIM3S09h2YK6gWA== X-Google-Smtp-Source: AGHT+IEy7LHeE27vl9WIdNN8TAFalU6lGLqSRL81CvZXvba5jmHKr8MbVut43YTi0kfBOO5ncTZ9H7TM8nIp4vtA4KY= X-Received: by 2002:a05:6102:4a8c:b0:4db:154f:aa02 with SMTP id ada2fe7eead31-4deed30ce38mr1415177137.1.1746740182375; Thu, 08 May 2025 14:36:22 -0700 (PDT) MIME-Version: 1.0 References: <20250508090735.39756-1-21cnbao@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Fri, 9 May 2025 09:36:11 +1200 X-Gm-Features: AX0GCFs7i0Fgmspd5yZQhwdm-Rw-CeN8l-Y8J88CN_rblOo8bSiZ0fXu9LaRc5k Message-ID: Subject: Re: [PATCH RFC] mm: userfaultfd: correct dirty flags set for both present and swap pte To: Lokesh Gidra Cc: Peter Xu , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , David Hildenbrand , Suren Baghdasaryan , Kalesh Singh Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Queue-Id: 696B940005 X-Rspamd-Server: rspam04 X-Stat-Signature: qkazu9yc8dy75whug9ssrfst38m4giko X-HE-Tag: 1746740183-162483 X-HE-Meta: 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 53qmUN1K 9IGlq6HUGsT0UD/ezDLQX3l0wW+aqXmNvV9qC6Zv9OfIHv902YzTeqTlY4uZm/gR9LiaJjJ/GSc4N9m57IA7698sOeHl7ggezCITiQGRr8u/b1hwYyyjvECyuQGT5SpE0z5dq5HZ6TXDCqZiZiJ0nrectkosW94YJgECNMg+//e4GT7oogYA7Sq/0WWLoraV96JeuIf81watHttAFJ7uLXxrlBxpRk3e2foFBe3BPBOzAQp2yI0VcA/z21GtK7QEg+Z39vSm9PCoZ5udlfav70oXfuUmL03Wac3oBd2FIADnkD3Os0qBYCPMreeR+/i5ofpuds22843VNCo4tt//Tc+sUw++STBXfqhqAPorob24+ho1fKSUgHl2x5d2uS/lvw9DAkybqKb336wdUyj8277IUygSdEd/xCS6H X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 9, 2025 at 3:27=E2=80=AFAM Lokesh Gidra wrote: > > Thanks Barry for fixing this. > > On Thu, May 8, 2025 at 8:24=E2=80=AFAM Peter Xu wrote= : > > > > On Thu, May 08, 2025 at 09:07:35PM +1200, Barry Song wrote: > > > From: Barry Song > > > > > > As David pointed out, what truly matters for mremap and userfaultfd > > > move operations is the soft dirty bit. The current comment and > > > implementation=E2=80=94which always sets the dirty bit for present PT= Es > > > and fails to set the soft dirty bit for swap PTEs=E2=80=94are incorre= ct. > > Can you please briefly describe the consequences of not setting the > soft-dirty bit? I'm wondering if it needs to be backported as a fix? As I understand it, this could break features like Checkpoint-Restore in Userspace (CRIU), which relies on tracking memory changes to create incremental dumps. While Android may not currently have a real-world use case for this, it would still be beneficial to backport the fix in a general way. > > > > This patch updates the behavior to correctly set the soft dirty bit > > > for both present and swap PTEs in accordance with mremap. > > > > > > Reported-by: David Hildenbrand > > > Closes: https://lore.kernel.org/linux-mm/02f14ee1-923f-47e3-a994-4950= afb9afcc@redhat.com/ > > > Cc: Peter Xu > > > Cc: Suren Baghdasaryan > > > Cc: Lokesh Gidra > > > Signed-off-by: Barry Song > > > > Acked-by: Peter Xu > > > > -- > > Peter Xu Thanks Barry