From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.zx2c4.com (lists.zx2c4.com [165.227.139.114]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E4980CF2561 for ; Tue, 18 Nov 2025 23:56:02 +0000 (UTC) Received: by lists.zx2c4.com (ZX2C4 Mail Server) with ESMTP id a544ba77; Tue, 18 Nov 2025 17:27:18 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.zx2c4.com (ZX2C4 Mail Server) with ESMTP id b2e9f276 for ; Tue, 26 Aug 2025 13:11:46 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7C1B82BF2; Tue, 26 Aug 2025 06:11:36 -0700 (PDT) Received: from raptor (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0B7A13F63F; Tue, 26 Aug 2025 06:11:36 -0700 (PDT) Date: Tue, 26 Aug 2025 14:11:34 +0100 From: Alexandru Elisei To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Alexander Potapenko , Andrew Morton , Brendan Jackman , Christoph Lameter , Dennis Zhou , Dmitry Vyukov , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux.dev, io-uring@vger.kernel.org, Jason Gunthorpe , Jens Axboe , Johannes Weiner , John Hubbard , kasan-dev@googlegroups.com, kvm@vger.kernel.org, "Liam R. Howlett" , Linus Torvalds , linux-arm-kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-ide@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Lorenzo Stoakes , Marco Elver , Marek Szyprowski , Michal Hocko , Mike Rapoport , Muchun Song , netdev@vger.kernel.org, Oscar Salvador , Peter Xu , Robin Murphy , Suren Baghdasaryan , Tejun Heo , virtualization@lists.linux.dev, Vlastimil Babka , wireguard@lists.zx2c4.com, x86@kernel.org, Zi Yan Subject: Re: [PATCH RFC 21/35] mm/cma: refuse handing out non-contiguous page ranges Message-ID: References: <20250821200701.1329277-1-david@redhat.com> <20250821200701.1329277-22-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Mailman-Approved-At: Tue, 18 Nov 2025 17:23:16 +0000 X-BeenThere: wireguard@lists.zx2c4.com X-Mailman-Version: 2.1.30rc1 Precedence: list List-Id: Development discussion of WireGuard List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: wireguard-bounces@lists.zx2c4.com Sender: "WireGuard" Hi David, On Tue, Aug 26, 2025 at 03:08:08PM +0200, David Hildenbrand wrote: > On 26.08.25 15:03, Alexandru Elisei wrote: > > Hi David, > > > > On Tue, Aug 26, 2025 at 01:04:33PM +0200, David Hildenbrand wrote: > > .. > > > > Just so I can better understand the problem being fixed, I guess you can have > > > > two consecutive pfns with non-consecutive associated struct page if you have two > > > > adjacent memory sections spanning the same physical memory region, is that > > > > correct? > > > > > > Exactly. Essentially on SPARSEMEM without SPARSEMEM_VMEMMAP it is not > > > guaranteed that > > > > > > pfn_to_page(pfn + 1) == pfn_to_page(pfn) + 1 > > > > > > when we cross memory section boundaries. > > > > > > It can be the case for early boot memory if we allocated consecutive areas > > > from memblock when allocating the memmap (struct pages) per memory section, > > > but it's not guaranteed. > > > > Thank you for the explanation, but I'm a bit confused by the last paragraph. I > > think what you're saying is that we can also have the reverse problem, where > > consecutive struct page * represent non-consecutive pfns, because memmap > > allocations happened to return consecutive virtual addresses, is that right? > > Exactly, that's something we have to deal with elsewhere [1]. For this code, > it's not a problem because we always allocate a contiguous PFN range. > > > > > If that's correct, I don't think that's the case for CMA, which deals out > > contiguous physical memory. Or were you just trying to explain the other side of > > the problem, and I'm just overthinking it? > > The latter :) Ok, sorry for the noise then, and thank you for educating me. Alex