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Fri, 8 May 2026 10:01:10 +0000 Message-ID: <89094011-fe78-40f9-9695-d50ee19167c5@windriver.com> Date: Fri, 8 May 2026 18:01:01 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] dma-mapping: remove bogus test for pfn_valid from dma_map_resource To: Robin Murphy , m.szyprowski@samsung.com Cc: leon@kernel.org, kbusch@kernel.org, jgg@ziepe.ca, 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> From: Jianpeng Chang In-Reply-To: <2dcc29d6-a4a9-4fdf-861d-312941ab0f07@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: KL1PR0401CA0014.apcprd04.prod.outlook.com (2603:1096:820:f::19) To DS0PR11MB7736.namprd11.prod.outlook.com (2603:10b6:8:f1::17) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=bi6dqmuHe4P4UrxVR6um:22 a=fTW__CHxibyLmBMfj2wP:22 a=NEAV23lmAAAA:8 a=t7CeM3EgAAAA:8 a=23wbk4N_KxE_iVXtykIA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=FdTzh2GWekK77mhwV6Dw:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-07_02,2026-05-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 bulkscore=0 adultscore=0 spamscore=0 priorityscore=1501 phishscore=0 clxscore=1015 lowpriorityscore=0 malwarescore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605080101 在 2026/5/7 下午9:18, Robin Murphy 写道: > CAUTION: This email comes from a non Wind River email account! > Do not click links or open attachments unless you recognize the sender > and know the content is safe. > > On 07/05/2026 4:21 am, 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. >> >> 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). >> >> The pfn_valid() check was originally removed by commit a9c38c5d267c >> ("dma-mapping: remove bogus test for pfn_valid from dma_map_resource") >> but was accidentally re-introduced by commit f7326196a781 >> ("dma-mapping: export new dma_*map_phys() interface") during the >> refactoring of dma_map_resource() into a wrapper around dma_map_phys(). >> >> Drop the pfn_valid() test from dma_map_resource() again. > > 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. Thanks, Jianpeng> > Thanks, > Robin. > >> Fixes: f7326196a781 ("dma-mapping: export new dma_*map_phys() interface") >> Signed-off-by: Jianpeng Chang >> --- >> Hi, >> >> I found the WARNING in dma_map_resource() on Raspberry Pi 4 when using >> the >> downstream kernel from https://github.com/raspberrypi/linux, which calls >> dma_map_resource() in bcm2835-dma.c (mainline uses the physical address >> directly instead). >> >> Although mainline bcm2835-dma does not call dma_map_resource(), the bogus >> pfn_valid() check can still affect any other driver that does, so it >> should be removed again. >> >> Thanks, >> Jianpeng >> >>   kernel/dma/mapping.c | 4 ---- >>   1 file changed, 4 deletions(-) >> >> 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); >