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Wed, 19 Mar 2025 08:15:33 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGw7muwol2OI7wSYL9a9iCyn+ZyN/NbRnjdL4AIqfECKKb7LsSD6rIVvzulorR8ijKfurSGNQLANVDULXCR0Sg= X-Received: by 2002:a05:6122:8d5:b0:520:51a4:b81c with SMTP id 71dfb90a1353d-525891bfc08mr2198425e0c.6.1742397332338; Wed, 19 Mar 2025 08:15:32 -0700 (PDT) MIME-Version: 1.0 References: <278393de-2729-4ed0-822c-87f33c7ce27e@redhat.com> <23000b6a-8a58-4c38-a032-ad62637d3fa4@lucifer.local> In-Reply-To: <23000b6a-8a58-4c38-a032-ad62637d3fa4@lucifer.local> From: Aleksandr Mikhalitsyn Date: Wed, 19 Mar 2025 16:15:21 +0100 X-Gm-Features: AQ5f1JqxdWeNnEOv-kQ64TqNajnS4hkxmZIQ-2f_7rOqGOdfJG9iC0RXfJ9SbYY Message-ID: Subject: Re: [PATCH v4 0/5] implement lightweight guard pages To: Lorenzo Stoakes Cc: David Hildenbrand , James.Bottomley@hansenpartnership.com, Liam.Howlett@oracle.com, akpm@linux-foundation.org, arnd@kernel.org, brauner@kernel.org, chris@zankel.net, deller@gmx.de, hch@infradead.org, jannh@google.com, jcmvbkbc@gmail.com, jeffxu@chromium.org, jhubbard@nvidia.com, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mattst88@gmail.com, muchun.song@linux.dev, paulmck@kernel.org, richard.henderson@linaro.org, shuah@kernel.org, sidhartha.kumar@oracle.com, surenb@google.com, tsbogend@alpha.franken.de, vbabka@suse.cz, willy@infradead.org, criu@lists.linux.dev, Andrei Vagin , Pavel Tikhomirov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: amjh44qgdk8w9hek848pmd13r6hrphs4 X-Rspamd-Queue-Id: 0752912001F X-HE-Tag: 1742397337-547061 X-HE-Meta: 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 EIX1gkVc Lq8zJoGSibhL7WIS5EU8gXNtE0wKjfPtqD+rVZcJKkG7GeA55cTgwHNDGOx4bjKFTXChejjKEAnNY/CvxlcfhdbwqXPCuullNgIz9u8e0yAB/JsxBO9hS5pmi/dAZJvVPGFwWJg+a3Al3QNRakLWvKTBDCS79RavRlBBMpH+Dq6G9iucR4ow5S0xLHpnTnzm5YPzkjDZRaXBverW9LCFqIgmLBLhQpWf4LbVGsmiAg59+XLKV1qSX9xQH6jf1ZbJx/nfJbly8rtQ/3L3x9hC4n99k4rEJJjSgQQHs8qBoc70MW4pTmI6QTWhPLfdBkEiMTZ61ywoBFSyyeAja9IJuC4IJ+GhAqTmZxyCFUpOmo+4ecW/vm9qJcbAhsPaGIZc5Qi/rg//HL0ailw8u8Hol4i9vKs07q+mYD4yxOO0X+IqniID6Tu+tIFljmD75HHulLOLs X-Bogosity: Ham, tests=bogofilter, spamicity=0.117482, 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 Wed, Mar 19, 2025 at 4:02=E2=80=AFPM Lorenzo Stoakes wrote: > > On Wed, Mar 19, 2025 at 03:52:56PM +0100, David Hildenbrand wrote: > > On 19.03.25 15:50, Alexander Mikhalitsyn wrote: > > > On Mon, Oct 28, 2024 at 02:13:26PM +0000, Lorenzo Stoakes wrote: > > [snip] > > > > > > > > Dear Lorenzo, > > > Dear colleagues, > > > > > > sorry about raising an old thread. > > > > > No worries! > > > > It looks like this feature is now used in glibc [1]. And we noticed f= ailures in CRIU [2] > > > CI on Fedora Rawhide userspace. Now a question is how we can properly= detect such > > > "guarded" pages from user space. As I can see from MADV_GUARD_INSTALL= implementation, > > > it does not modify VMA flags anyhow, but only page tables. It means t= hat /proc//maps > > > and /proc//smaps interfaces are useless in this case. (Please, c= orrect me if I'm missing > > > anything here.) > > Sorry to hear that. No problem at all ;) > > > > > > > I wonder if you have any ideas / suggestions regarding Checkpoint/Res= tore here. We (CRIU devs) are happy > > > to develop some patches to bring some uAPI to expose MADV_GUARDs, but= before going into this we decided > > > to raise this question in LKML. > > There's no need. > > > > > > > See [1] and [2] > > > > [1] > > https://lkml.kernel.org/r/cover.1740139449.git.lorenzo.stoakes@oracle.c= om > > [2] https://lwn.net/Articles/1011366/ > > As per David, there is already a feature heading for 6.15 which will allo= w > this to be exposed by /proc/$pid/pagemap. Yeah, that's indeed very helpful! > > In addition, I plan to add a 'maybe has guard regions' flag that can be > observed in smaps to assist narrowing down which VMAs to check. > > However unfortunately due to the nature of the feature there is no gettin= g > around the need to traverse page tables. > > That thread (and LWN article :) go into extensive detail as to why. In > essence - it's the basis of its design to express this information at the > page table level only, and any attempt to encode this at the VMA level > (other than a 'maybe' flag) would eliminate the purpose of the feature. Thank you very much for these explanations! I'll read the LWN article too. > > Let me know if there's any way I can help! Keep in contact! ;) Kind regards, Alex > > Cheers, Lorenzo > > > > > > > -- > > Cheers, > > > > David / dhildenb > >