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Fri, 01 May 2026 12:38:35 -0700 (PDT) Date: Fri, 1 May 2026 19:38:34 +0000 From: Pasha Tatashin To: David CARLIER Cc: Pasha Tatashin , 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 Message-ID: References: <20260423125648.152113-1-devnexen@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: D857E20003 X-Rspamd-Server: rspam06 X-Stat-Signature: iix46nupeaeacirgxdrpqub7kjbcxs1j X-HE-Tag: 1777664316-64231 X-HE-Meta: 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 ldfFCn6w 7/9wBUpHLw49kavTPAX9lKu70de2x1mW5AopkuWOzRFGHVKXIN2n2xg+04EYwrKRPb0QldETtsAbatmSEb540jDr1SdUhM2OOT1QHpKDNkW9GJ17b5CAfuILztCWFcDgQcdAUbyF+JgzsKLARu6fSF4c/rK93Ekq6vmzfybmgTnGIphum8BPhLhVTuu4N3mJaX1KEemoxJmZ82EYuIIdJmUUu2l+JhbtJYIzj1V2um9FNnniSY2xc7GcNhr7a60WTBoZjQcUSfi6uATkndNYK7ZCX0GXelqhUAhGk/SsU1+QfjDvK3pHfnUD3ubYo6sLoPP+9WsUwh/wtCNhe2UDgsyMFjFP4ZTqmppE1zEuK89/17oZ9uGb+jGjlOBH6whoAP/NILfCjvn8C474mPiiGncuQiEVFmfyfUTMP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Reviewed-by: Pasha Tatashin