From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 5DB30363C6C; Fri, 8 May 2026 12:16:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778242591; cv=none; b=lIoz9As+ZQAzw6+G1p40n+sCPLo2dT+miCatKiOHF6vufM4mryQdDstZH/Ys09HcZ1ZfNt9e3FBztiML2jROZMQOm5KV43wvyDFk6c/fe1J3OiTgRhyNzApB70/SK09S30O70s5WrN7kiwUrQWoHeb/HLCe6ibuNDGtGXH1xnzU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778242591; c=relaxed/simple; bh=HbTupgDMI57jkZxLiL4IdpGCIDjjMhZjnIHjIezty50=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JYOU4XCfy75+YpF1iBP3MOWovoRVfQWJ84GiAsJ7l87yxLxYGCoTLNxRNh85y9MhmApOcIlrUpJ88VILvErAWZrjXyFDcIKIoiADQ3YNoDRRdQm8g1vzdkwJ5DSpPug3gPSuqHg1+M+T1kBk4Gm4h8C4LrQn09Bbz7ZYoAG1r/4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=icrLRbdL; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="icrLRbdL" 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 18EAF1BCA; Fri, 8 May 2026 05:16:23 -0700 (PDT) Received: from [10.57.63.248] (unknown [10.57.63.248]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3E9813F763; Fri, 8 May 2026 05:16:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1778242588; bh=HbTupgDMI57jkZxLiL4IdpGCIDjjMhZjnIHjIezty50=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=icrLRbdLBTqGmRZrGCpNV0w9uRuKVvRNaT3O0/INRkfmQokvUSd0d2Dg9ZTb4Lp2z qClzYe3kBdA7W0afgCBlUiG3wtVGIkmD7c6MKqNitK57ToXXeglg0RV2KCCjPJlfjv YaqJH/0o5pawmQ/XB4kWuEpxzeE18mRDlLV+ZgrI= Message-ID: <662fdf07-6475-4807-94b0-54b3b439ae1c@arm.com> Date: Fri, 8 May 2026 13:16:25 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] dma-mapping: remove bogus test for pfn_valid from dma_map_resource To: Jason Gunthorpe , Jianpeng Chang Cc: m.szyprowski@samsung.com, leon@kernel.org, kbusch@kernel.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260507032120.4072283-1-jianpeng.chang.cn@windriver.com> <2dcc29d6-a4a9-4fdf-861d-312941ab0f07@arm.com> <89094011-fe78-40f9-9695-d50ee19167c5@windriver.com> <20260508113100.GA9285@ziepe.ca> From: Robin Murphy Content-Language: en-GB In-Reply-To: <20260508113100.GA9285@ziepe.ca> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2026-05-08 12:31 pm, Jason Gunthorpe wrote: > On Fri, May 08, 2026 at 06:01:01PM +0800, Jianpeng Chang wrote: >>> As I said last time, I think pfn_valid() && !PageReserved(pfn_to_page()) >>> would be enough for what we want here, although now it's strictly under >>> CONFIG_DMA_API_DEBUG, perhaps the overhead of memblock_is_map_memory() >>> might be less of an issue. Either way though, now that it's all >>> channelled through the single dma_map_phys() path, it would probably >>> make sense to consolidate any MMIO sanity-checking into >>> dma_debug_map_phys() anyway :/ > >> Thanks for the suggestion. Move the check into debug_dma_map_phys() is >> indeed better, and I will replace pfn_valid() with pfn_valid() && >> !PageReserved() as you suggested. > > I'm not sure that is right. IIRC pfn_valid() is true for ZONE_DEVICE > P2P pages that are used with map_phys but never with map_resource. > > PageReserved isn't enough to fix it. It fixes the false-positive on non-reserved pages, which is the important thing. Yes, we'll get false-negatives on reserved ZONE_DEVICE pages and similar, but that's still an improvement over getting false-negatives on _everything_ by not checking at all. Realistically, dma-debug can never be exhaustive and 100% accurate, but there's still value in catching as much obvious misuse as is straightforward to do. In the long term, perhaps we could add some kind of "DMAable memory/P2Pable MMIO/neither" attribute to our wishlist of physical address range properties along with CoCO shared/private, such that dma_map_phys() could then do the right thing all by itself and we wouldn't even need DMA_ATTR_MMIO any more... Thanks, Robin.