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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RyvOPtCrsaxhbwyyXJ9/sJxTBCYbXkxvMc+iFf5L1/ntPvY+woD6bO16mABcc9fzV TRRjRLZAcc2Nn8wIqx41NvyZRgmTLLMoST3hzqBUZIzl1WOZ+HRkzq+Y0o3H08c2yb TuGDO7ocWaI0p0OlB0jJ5cAO9ZDJxmYha4jc0j0g= Message-ID: <75f65aa7-4f89-4ef8-8941-51b1d54d1ad3@arm.com> Date: Wed, 1 Apr 2026 16:26:14 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] dma-debug: suppress cacheline overlap warning when arch has no DMA alignment requirement To: Andy Shevchenko Cc: Marek Szyprowski , Mikhail Gavrilov , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, linux-mm@kvack.org, harry@kernel.org, vbabka@kernel.org, akpm@linux-foundation.org, stern@rowland.harvard.edu, linux@roeck-us.net, hch@lst.de, Jeff.kirsher@gmail.com, catalin.marinas@arm.com References: <20260327124156.24820-1-mikhail.v.gavrilov@gmail.com> <6270d4f0-85e4-496d-8db4-87ccb791ca4d@samsung.com> From: Robin Murphy Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 0BB0B140009 X-Stat-Signature: dfskjkjmi71iw4gahkz4inc3uj3ewe8x X-Rspamd-Server: rspam06 X-HE-Tag: 1775057180-423295 X-HE-Meta: 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 TS9zo3fi qFVBwK6XmU95X5PYeCHQlccSKzBGPzelEwuT+P6J3Za/jvrsfiAKAz3X3/d86kxVpnJGbN8p4qHQYudC/2H3qek0xUWCk4rIxanL7PJeVPw9tu042zMeM6HywnRysNgqmWFeoCDwNLYFbDgog1GmaydF+ItHPcDnVk77940UGiep+6lv776pk0N8jCQaI/NLauXuxHvhCfes2LBjm33BZsF4e5FPfiHDw7xOho1rAhBNR3ASaNlMaa36f1N07BLUS7LoYInHmiA2XXZixN+zSrJVbAJPOyThtgCiJjBlh9bp5nG9GR+TArPc5P6u4b3le2TOem+pWSKQHbzsX4GF7Gh7KB1g8jE/nSfjCr1cTnPTRXEUqU5UIHLbj6TtVPDFJgavc8ltm10Douq4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026-04-01 2:25 pm, Andy Shevchenko wrote: > On Wed, Apr 1, 2026 at 3:11 PM Robin Murphy wrote: >> On 2026-03-30 8:44 am, Marek Szyprowski wrote: >>> On 27.03.2026 13:41, Mikhail Gavrilov wrote: > > ... > >> TBH I'd be inclined to have CONFIG_DMA_DEBUG raise ARCH_DMA_MINALIGN as >> appropriate such that genuine false-positives can't happen, rather than >> effectively defeat the whole check, > > I dunno if you read v1 thread, where I proposed to unroll the check > and use pr_debug_once() for the cases which we expect not to panic, > but would be good to have a track of. I had not seen v1, as I took the last 3 days off and hadn't got that far up my inbox yet - I guess it's at least reassuring to have reached similar conclusions independently :) The fundamental issue here is that dma-debug doesn't realistically have a way to know whether the thing being mapped is intentionally a whole dedicated kmalloc allocation - where we can trust SLUB (and DMA_BOUNCE_UNALIGNED_KMALLOC if appropriate) to do the right thing across different systems - or just something which might happen to line up by coincidence on someone's development machine, but for portability they definitely do still need to take explicit care about (e.g. struct devres::data). Certainly some milder and/or opt-in reporting of potential-false-positive overlaps wouldn't be a terrible idea, if someone wants to have a crack at it. Thanks, Robin.