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AJvYcCVHxQd53dxDcSVcHPqNc+8Cq87X1JIqlRQyfQErH85HmMrPkyxMbJIeABpwGxnk+iYo83+GIxHQ9w==@kvack.org X-Gm-Message-State: AOJu0Ywkxf+rPKcsAZSd9sO9UOWMZ1vEvJMMLgPin+k+zmxnGr6oYUlj svj+pQCpUrG9WRJ0GYlwrb9xBB/RDZqGKPMuOIF6nyrsr563/rs5e3Dxbe4Bcf+xje/IMCxNJMa gcUHNNY7+V4QKaw2GhVpwqFCZhJqSFMWSYO+Q X-Gm-Gg: ASbGncsN8ZEpnhEmcYJRSL7T1K/O6WAK5/zBV/FClk5+uWnZ/2Ih1IoBLvm9DyQ2a2/ JdZyVv57N1WwjXPkV42XUtl89h4EVj69x/xAt3iCBRaoG5Gy2M3wLCxM9o1WUcsqDFdb2T4a1/0 EvDZH0y0DIO9CdPBpwujGkDHYNVkLSwVIwOCfrvW0a8nMeYcV+Mxo= X-Google-Smtp-Source: AGHT+IEgqsrWQUA9rdeo3kuLeufSbMfNQwE/56BObevaH3Yn2x2Uznm7M/g+3rok3OqVMrMP3b5YzchOsh92luUxKMw= X-Received: by 2002:a05:6402:128a:b0:5fb:89b1:717f with SMTP id 4fb4d7f45d1cf-5fca18fcc39mr32041a12.0.1746741647706; Thu, 08 May 2025 15:00:47 -0700 (PDT) MIME-Version: 1.0 References: <20250508090735.39756-1-21cnbao@gmail.com> In-Reply-To: From: Lokesh Gidra Date: Thu, 8 May 2025 15:00:36 -0700 X-Gm-Features: ATxdqUGEAHdTjxmi3Y7ZoVNdjW68Vcol4AF7ledDZS6qmSnUbnYiR7JvZuwMaUY Message-ID: Subject: Re: [PATCH RFC] mm: userfaultfd: correct dirty flags set for both present and swap pte To: Barry Song <21cnbao@gmail.com> 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-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 8B58E4000F X-Stat-Signature: qz4jt96f43qeb4o81yb9w3fofyztu3ko X-Rspam-User: X-HE-Tag: 1746741649-951267 X-HE-Meta: U2FsdGVkX1+tLyWCqbmunCXDjikH6qI21u6RcMmIYPkUmTc+TsBGTG0SmZEJeksAZ1E7dO4LvfHrDtsqNfDVr/nbJHniGoxYOFpz8HeuY5c26g/QjkwMGfL79/Ym15uq7UqOtJCddT8QMeB62PkhYzd/9CqXErzelxsjUlfPEF2EH9nPwiPqCGsKW3i8eoG0LFH8esfHQl/yqD64fUNQw3wj5iq6qKTX8MIgDj/GL0YszLtnILywN9nGuTNb3p8NHk0Dq0Y/4KiTj0Krre62W4JWWr+U3lMlp+K49mprPSN0DPeV78+lwwPmIW4vc9cVmQakqPXnEuZCH0egNsEPtnI5RR9wf1/27s6aIbL+bURRnm+WchtaV09OCJ6cDpqlhaowi5/fHPp0VTQyJ4DEGUSFdqdBILt4q+1zuLcM7CszpIxPS98sB4S7gNw/EFEJifpwlfYQTK0tr0XGHRSUUK0ZfpuuU5M/BN0bAJt4XSJ4hKi70SKjAtwhUuO4zpEfpM3GAQL23rwTwdsvdSQ7wdETLU9+MKZVJK+AaoCoGYeKCCRz7BaRzAFFeuF2MNvNz5zI79KmbV2WF+gsV5IqoFZQtEDRAb4m5qQObTJ5dVyQ2YvcqymuZlGcE2SV8La5MWMSRWgTWGJtbSGWWynwyO/Ds/xsXaoRytvOzSH8ghhHSErHyaPr/AQhArA9bUQaMZz5/3+kmp197HJd3ahOfl59LX2wC1QtfaYwJPAc7sl3D/Fi61T2Cc0PG+1UueugSSoX2KEQ611icC2rHjNZR5Ugjo0x+yFC6vcoU6/84BpC9C4CzqGfffRMvoO61MNFS+RaHvsXocSUVuhBMw/5YuyuUKNLYx4yQvonCB235f1Ziwl30+o6nHlPFMOAhSUXnDoDwMwg+929S4KLUz8zl1cb2N+uZZHXW0qnkL0Gre3Uws9xqAStbJ9ttK5ClvMY2a8cwik4hXWEwfq9YMf ZUVXm96R jZ1grm2VAf832qB9K1pbd+mqcogF4nM0Ky3Vd/6WMEDKjtaFCevY30RtxNT7SozLsV9xDHTwTxBvnKL7uH+CNCrRk8Ba8tQPhaKatyIwge5rjnvb/oThnVcZlgAtrCRKXa3Z4JoNNGTBjwQfxBWNh1MGzlA3OORwUQGg9yx1iw9+KA9au+rn87cw4ix3bSivUe2CcJFp0TojgKpSVnwU54aLBkqaczi7SAHY57mlKL1jbVkv/rhr+lM7rJ9Xky1cI6YzGFOnBVxVqdc03EJSXJJNwiCwlsfxDBxV6GRX1Fn8VszI52jLOdV0jGg== 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 Thu, May 8, 2025 at 2:36=E2=80=AFPM Barry Song <21cnbao@gmail.com> wrote= : > > 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 wro= te: > > > > > > 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 = PTEs > > > > and fails to set the soft dirty bit for swap PTEs=E2=80=94are incor= rect. > > > > 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. > Makes sense. Thanks for clarifying. > > > > > > 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-a994-49= 50afb9afcc@redhat.com/ > > > > Cc: Peter Xu > > > > Cc: Suren Baghdasaryan > > > > Cc: Lokesh Gidra > > > > Signed-off-by: Barry Song > > > > > > Acked-by: Peter Xu > > > > > > -- > > > Peter Xu > > Thanks > Barry