From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0256A36D9F8; Mon, 11 May 2026 17:56:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778522208; cv=none; b=AcdN+chxQuFlHL/j1+VdTRvq2lQLTxbWP3UbMREkRY40zm872Nmkk6NouPtFbOcMsl73VUauS3Mkko7aEtpw1KIJ8g6L687nRVPxO/7s83aOb2Ez0khIuRL4e/cq7+UHFoH5RJEnyGyaUqM+UzoDAsPN9GZwPORVFeIhDZnHcM4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778522208; c=relaxed/simple; bh=wWPR3Z3pINbn3KtsYC+19U2lza/TgQV1Wvb7U7l2jmw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=X7OeOaPrlHTIDdXz0l3m8I1ZyVd3HGFCefP981b/KsnZr27OUij3XC29A0KaKI+A2kz58b7OnrTs7nR+AqA8zsWONYq0k1Koy4tKprF/l3dEUiyJC6lkQn7wVKgO5W7fLVP0cpcVaX9t6FFKUsRCjBHFMVfaxrRqsCXvSK7XOOE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ju5nl9OE; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ju5nl9OE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F0B3CC2BCF5; Mon, 11 May 2026 17:56:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778522207; bh=wWPR3Z3pINbn3KtsYC+19U2lza/TgQV1Wvb7U7l2jmw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ju5nl9OETjvrFQmOEPGPKlDirxEP18xoxFYafD21aUX0IT3KSmhitqE4dTjsk0Jbd uzUPkPWKF+qD7pvydhtFjOttblywKU/+fc5zcKUt25DUKAyyvoB8WAP4t5L7DAv7oY pfmCIVYTo6Elh6m8n20HB2QnUfVgWKVr59A8SQY45IoDlb7cATRhgaI1C9NKzl34NN eOS0a+4mJ94Q7FO77OSpuFVDuQo1W/b/3aJORsVaE7CaYOEVYO1KpBOfSydU+yHlZD rxK7t0g9YCSkhm9/VC0/sE5pCl8GOcVrn7fGh4TWiQJ+I+B25/7JxC4CNJPjEXh9H6 FXSOGS489jxyg== Date: Mon, 11 May 2026 20:56:41 +0300 From: Leon Romanovsky To: Jianpeng Chang Cc: m.szyprowski@samsung.com, robin.murphy@arm.com, kbusch@kernel.org, jgg@ziepe.ca, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] dma-mapping: move dma_map_resource() sanity check into debug code Message-ID: <20260511175641.GL15586@unreal> References: <20260511083133.1096171-1-jianpeng.chang.cn@windriver.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260511083133.1096171-1-jianpeng.chang.cn@windriver.com> On Mon, May 11, 2026 at 04:31:33PM +0800, Jianpeng Chang wrote: > dma_map_resource() uses pfn_valid() to ensure the range is not RAM. > However, pfn_valid() only checks for availability of the memory map for > a PFN but it does not ensure that the PFN is actually backed by RAM. On > ARM64 with SPARSEMEM (128MB section granularity), MMIO addresses that > share a section with RAM will falsely trigger the WARN_ON_ONCE and cause > dma_map_resource() to return DMA_MAPPING_ERROR. > > This causes a WARNING on Raspberry Pi 4 during spi_bcm2835 probe because > the SPI FIFO register (0xfe204004) falls in the same sparsemem section > as the end of RAM (0xf8000000-0xfbffffff), both in section 31 > (0xf8000000-0xffffffff). > > Move the sanity check from dma_map_resource() into debug_dma_map_phys() > and replace the unreliable pfn_valid() with pfn_valid() && > !PageReserved(), which correctly identifies actual usable RAM without > false positives for MMIO regions that happen to have struct pages. > > Since dma_map_resource() is dma_map_phys(DMA_ATTR_MMIO), the check > applies equally to both APIs. Any non-reserved page represents kernel > memory to a sufficient degree that using DMA_ATTR_MMIO on it is almost > certainly wrong and risks breaking coherency on non-coherent platforms. > ZONE_DEVICE pages used for PCI P2P DMA (MEMORY_DEVICE_PCI_P2PDMA) have > PageReserved set, so they will not trigger a false positive. > > The check is now a WARN_ONCE that no longer blocks the mapping, since > being unobtrusive is more important than being exhaustive for what is > merely a debug sanity check. > > Fixes: f7326196a781 ("dma-mapping: export new dma_*map_phys() interface") > Signed-off-by: Jianpeng Chang > --- > v2: > - move check to debug_dma_map_phys and replace pfn_valid() with > pfn_valid() && !PageReserved() as Robin suggested. > - update commit message to explain why PageReserved is safe for > ZONE_DEVICE PCI_P2PDMA pages > v1: https://lore.kernel.org/all/20260507032120.4072283-1-jianpeng.chang.cn@windriver.com/ > kernel/dma/debug.c | 9 +++++++++ > kernel/dma/mapping.c | 4 ---- > 2 files changed, 9 insertions(+), 4 deletions(-) > > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c > index 1a725edbbbf6..180aa2c930b5 100644 > --- a/kernel/dma/debug.c > +++ b/kernel/dma/debug.c > @@ -1239,6 +1239,15 @@ void debug_dma_map_phys(struct device *dev, phys_addr_t phys, size_t size, > if (dma_mapping_error(dev, dma_addr)) > return; > > + if (attrs & DMA_ATTR_MMIO) { > + unsigned long pfn = PHYS_PFN(phys); > + > + WARN_ONCE(pfn_valid(pfn) && !PageReserved(pfn_to_page(pfn)), > + "dma_map_resource called for RAM address %pa\n", > + &phys); > + return; I’m not comfortable with this return statement. It effectively disables DMA debugging for any caller that uses dma_map_phys(..., DMA_ATTR_MMIO), like dma-buf, block layer, HMM, e.t.c Thanks > + } > + > entry = dma_entry_alloc(); > if (!entry) > return; > diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c > index 23ed8eb9233e..e6b07f160d20 100644 > --- a/kernel/dma/mapping.c > +++ b/kernel/dma/mapping.c > @@ -365,10 +365,6 @@ EXPORT_SYMBOL(dma_unmap_sg_attrs); > dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr, > size_t size, enum dma_data_direction dir, unsigned long attrs) > { > - if (IS_ENABLED(CONFIG_DMA_API_DEBUG) && > - WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr)))) > - return DMA_MAPPING_ERROR; > - > return dma_map_phys(dev, phys_addr, size, dir, attrs | DMA_ATTR_MMIO); > } > EXPORT_SYMBOL(dma_map_resource); > -- > 2.54.0 >