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[34.87.188.174]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82f8ec24850sm26334037b3a.60.2026.04.24.22.36.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Apr 2026 22:36:20 -0700 (PDT) Date: Sat, 25 Apr 2026 05:36:15 +0000 From: Pranjal Shrivastava To: Mostafa Saleh Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org, joro@8bytes.org, robin.murphy@arm.com, will@kernel.org, jgg@ziepe.ca, baolu.lu@linux.intel.com, kevin.tian@intel.com Subject: Re: [PATCH] iommu/pages: Fix iommu_pages_flush_incoherent() for non-x86 Message-ID: References: <20260424115051.2082174-1-smostafa@google.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=us-ascii Content-Disposition: inline In-Reply-To: <20260424115051.2082174-1-smostafa@google.com> On Fri, Apr 24, 2026 at 11:50:51AM +0000, Mostafa Saleh wrote: > The dma_sync_single_for_device() function expects a dma_addr_t, but > iommu_pages_flush_incoherent() was incorrectly passing a virtual > address. > > Since iommu_pages_start_incoherent() enforces a 1:1 mapping between > DMA addresses and physical addresses (checked via WARN_ON), we can > convert the virtual address to a physical address before passing it to > the DMA API. > > This also matches the behaviour of the other non-x86 in > iommu_pages_free_incoherent(), which uses virt_to_phys(virt); > > Fixes: 36ae67b13976 ("iommu/pages: Add support for incoherent IOMMU page table walkers") > Signed-off-by: Mostafa Saleh > --- > drivers/iommu/iommu-pages.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iommu/iommu-pages.h b/drivers/iommu/iommu-pages.h > index ae9da4f571f6..e9e605b5fa3a 100644 > --- a/drivers/iommu/iommu-pages.h > +++ b/drivers/iommu/iommu-pages.h > @@ -137,7 +137,7 @@ static inline void iommu_pages_flush_incoherent(struct device *dma_dev, > void *virt, size_t offset, > size_t len) > { > - dma_sync_single_for_device(dma_dev, (uintptr_t)virt + offset, len, > + dma_sync_single_for_device(dma_dev, virt_to_phys(virt) + offset, len, > DMA_TO_DEVICE); > } > void iommu_pages_stop_incoherent_list(struct iommu_pages_list *list, Nice catch! Additionally, I think we should update the comment in iommu_pages_start_incoherent() to clarify the restriction. The current comment says: "The DMA API is not allowed to do anything other than DMA direct." But dma_direct actually handles bus offsets perfectly fine. However, this code fails on platforms with a bus offset is because of the strict check: WARN_ON(dma != virt_to_phys(virt)) which enforces a strict 1:1 mapping. So saying that we only allow dma_direct is a bit misleading as to why bus offsets fail here. We should update that comment to something like: diff --git a/drivers/iommu/iommu-pages.c b/drivers/iommu/iommu-pages.c index 3bab175d8557..3904de686206 100644 --- a/drivers/iommu/iommu-pages.c +++ b/drivers/iommu/iommu-pages.c @@ -161,9 +161,11 @@ int iommu_pages_start_incoherent(void *virt, struct device *dma_dev) return -EINVAL; /* - * The DMA API is not allowed to do anything other than DMA - * direct. It would be nice to also check - * dev_is_dma_coherent(dma_dev)); + * We enforce a strict 1:1 mapping (dma == phys). This means + * platforms with a bus offset or those that require translation for + * the IOMMU's own memory are not supported, even though dma_direct + * could otherwise handle bus offsets. + * It would be nice to also check dev_is_dma_coherent(dma_dev)); */ if (WARN_ON(dma != virt_to_phys(virt))) { dma_unmap_single(dma_dev, dma, ioptdesc_mem_size(iopt), For the fix: Reviewed-by: Pranjal Shrivastava Thanks, Praan