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b=clZ63voxCVThA2Nayvoz6O+UjlaA9DDU4Mg62Y9ygdASi3msfm1CYKGs+EcrWNGBQ lHa5GoSoNErp+EGBY2I/bUxz+SXw4R7WTmY/U3Kv63VZr1iQJ7ZGNHOCIbPoC+XSw6 We7p6jpbb+JUT2RJ14DRdJ+bwwvWJJpPf/T5RjMpLPsx+jwXhDbC8ewjXrjh+buNwm k/BIyAUEXM3fqEHRIvYnohEL8e1IMenHmlyS5jaPCNvBjCGfaK74GtBX3gTFbc+sXn 2r9xtNjKPPzeBlb2gTkAMynxUc9I6hF83hwP0aVQYiP5Jc/UgSiiLgy2kOl9rl3yWy eBromN4hOqA3g== From: Pratyush Yadav To: Pasha Tatashin Cc: David CARLIER , akpm@linux-foundation.org, pratyush@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm/memfd_luo: reject memfds whose page count exceeds UINT_MAX In-Reply-To: (Pasha Tatashin's message of "Fri, 1 May 2026 19:38:34 +0000") References: <20260423125648.152113-1-devnexen@gmail.com> Date: Mon, 04 May 2026 10:05:03 +0200 Message-ID: <2vxzo6iv38i8.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Rspamd-Queue-Id: 9145C1C0009 X-Rspamd-Server: rspam04 X-Stat-Signature: cdtb46t8wxwc7zxjqs16kcgb8f4r8e7x X-HE-Tag: 1777881906-109704 X-HE-Meta: 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 CeOzI76F xw8sEIHQbwZm+yIPU62mHgQZcmnWAc4HqP+hdxv2/300QvQnJ6IFj0gEHBAxp5SkC914q7YUJGu5qEITOqfIQoDa+ZWvZJuqshNjYQxIYkGVUATpN1nfNiI8MiwUaEmEKwrVvrc9Pu4iU8m7KURVkhIPkWdo37TFZ1guZakstmKsbi44goqjsagAkys2/Nbx09PAtHN43LBtl8paHsvXZeGd20/JS+2qrV60/CfD34yowE1ktaa09pjGCoAFZOyNaWQsah2dH8cjxrh4ywp3Osf/q/6kyzbhlsqw1k9I23OYlJJY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 01 2026, Pasha Tatashin wrote: > On 05-01 20:26, David CARLIER wrote: >> On 2026-05-01 18:59, Pasha Tatashin wrote: >> > I think, the fix should be first done at memfd_pin_folios() to >> change >> > max_folios to 'long' or 'unsigned long', and then just updated >> > memfd_luo.c to match. >> >> Even with memfd_pin_folios() widened, memfd_luo_preserve_folios() >> still >> kvmalloc_objs()s the folios array up front -- at UINT_MAX entries >> that's >> already ~32 GiB of pointer array, which won't realistically succeed. >> So >> the guard here still makes sense, just on allocation grounds rather than >> interface truncation. >> >> Happy to widen memfd_pin_folios() as a separate patch, but I'd keep >> the >> -EFBIG check regardless. Or did you have a different shape in mind? > > Ah, Good point about kvmalloc_objs(), I am not against this, even though > it is a very theoretical issue. Yeah. I plan to get rid of the pinning anyway and do this via the page cache directly (might be easier said than done though), so this should be fine for now I think. I suspect we might run into a lot more problems if we get a memfd like this anyway. Reviewed-by: Pratyush Yadav > > Reviewed-by: Pasha Tatashin -- Regards, Pratyush Yadav