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Wed, 9 Sep 2026 03:25:08 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ThreadId: AMXrPpDe2nhJ Date: Wed, 09 Sep 2026 09:24:23 +0200 From: "Arnd Bergmann" To: "Karl Mehltretter" , "Russell King" Cc: "Nicolas Pitre" , "Marek Szyprowski" , "Robin Murphy" , iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Message-Id: In-Reply-To: <20260909064443.90544-1-kmehltretter@gmail.com> References: <20260909064443.90544-1-kmehltretter@gmail.com> Subject: Re: [PATCH] ARM: dma-mapping: split cache maintenance at highmem boundary Content-Type: text/plain Content-Transfer-Encoding: 7bit On Wed, Sep 9, 2026, at 08:44, Karl Mehltretter wrote: > dma_cache_maint_page() processes highmem pages one at a time, but passes > the complete remaining range to a cache operation when the current page > is lowmem. If a physically contiguous range starts in lowmem and crosses > into highmem, the operation continues beyond high_memory through virtual > addresses which do not map the highmem pages. > > On a Raspberry Pi 400 running an ARM32 LPAE kernel, an 8 KiB scatterlist > entry crossing this boundary caused a deterministic data abort at f0000000 > in v7_dma_clean_range(). > > Limit the crossing lowmem iteration to the end of its page. Subsequent > iterations advance page by page until the existing highmem path takes > over. Keep the bulk operation for ranges contained in lowmem. > > Fixes: 43377453af83 ("[ARM] introduce dma_cache_maint_page()") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Karl Mehltretter Hi Karl, I can see how the fix addresses the problem, but I don't yet see how you can arrive in this situation. What type of memory allocation can produce a physically contiguous page range from multiple zones? Arnd