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Tue, 09 Jun 2026 06:12:26 -0700 (PDT) Date: Tue, 9 Jun 2026 15:12:22 +0200 From: Petr Tesarik To: "Aneesh Kumar K.V (Arm)" Cc: iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, Robin Murphy , Marek Szyprowski , Will Deacon , Marc Zyngier , Steven Price , Suzuki K Poulose , Catalin Marinas , Jiri Pirko , Jason Gunthorpe , Mostafa Saleh , Alexey Kardashevskiy , Dan Williams , Xu Yilun , linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , x86@kernel.org, stable@vger.kernel.org, Michael Kelley Subject: Re: [PATCH v6 14/20] dma-direct: return struct page from dma_direct_alloc_from_pool() Message-ID: <20260609151222.476a5521@mordecai> In-Reply-To: <20260604083959.1265923-15-aneesh.kumar@kernel.org> References: <20260604083959.1265923-1-aneesh.kumar@kernel.org> <20260604083959.1265923-15-aneesh.kumar@kernel.org> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-suse-linux-gnu) Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 4 Jun 2026 14:09:53 +0530 "Aneesh Kumar K.V (Arm)" wrote: > Commit 5b138c534fda ("dma-direct: factor out a dma_direct_alloc_from_pool > helper") changed dma_direct_alloc_from_pool() to return the CPU address > from dma_alloc_from_pool(). That fits dma_direct_alloc(), but > dma_direct_alloc_pages() also uses the helper and expects a struct page *. > > Fix this by making dma_direct_alloc_from_pool() return the struct page * > again, and pass the CPU address back through an out-parameter for the > dma_direct_alloc() caller. > > Fixes: 5b138c534fda ("dma-direct: factor out a dma_direct_alloc_from_pool helper") > Cc: stable@vger.kernel.org While I totally agree with the reasoning and the fix, it's interesting that this bug has been apparently present in the kernel for 5+ years without anybody hitting nasty memory corruption bugs. How can it be? Is the buggy code path never actually used in practice? Does it hint at a missed opportunity to simplify the code? Anyway, these these thoughts are intended for a possible future cleanup. For now, let's apply the fix as is, of course. Petr T > Tested-by: Michael Kelley > Tested-by: Mostafa Saleh > Signed-off-by: Aneesh Kumar K.V (Arm) > --- > kernel/dma/direct.c | 21 ++++++++++++--------- > 1 file changed, 12 insertions(+), 9 deletions(-) > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > index 4e446aa4130e..e0ab9ff3f1d6 100644 > --- a/kernel/dma/direct.c > +++ b/kernel/dma/direct.c > @@ -157,24 +157,24 @@ static bool dma_direct_use_pool(struct device *dev, gfp_t gfp) > return !gfpflags_allow_blocking(gfp) && !is_swiotlb_for_alloc(dev); > } > > -static void *dma_direct_alloc_from_pool(struct device *dev, size_t size, > - dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs) > +static struct page *dma_direct_alloc_from_pool(struct device *dev, size_t size, > + dma_addr_t *dma_handle, void **cpu_addr, gfp_t gfp, > + unsigned long attrs) > { > struct page *page; > u64 phys_limit; > - void *ret; > > if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_DMA_COHERENT_POOL))) > return NULL; > > gfp |= dma_direct_optimal_gfp_mask(dev, &phys_limit); > - page = dma_alloc_from_pool(dev, size, &ret, gfp, attrs, > + page = dma_alloc_from_pool(dev, size, cpu_addr, gfp, attrs, > dma_coherent_ok); > if (!page) > return NULL; > *dma_handle = phys_to_dma_direct(dev, page_to_phys(page), > !!(attrs & DMA_ATTR_CC_SHARED)); > - return ret; > + return page; > } > > static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size, > @@ -270,9 +270,12 @@ void *dma_direct_alloc(struct device *dev, size_t size, > * the atomic pools instead if we aren't allowed block. > */ > if ((remap || (attrs & DMA_ATTR_CC_SHARED)) && > - dma_direct_use_pool(dev, gfp)) > - return dma_direct_alloc_from_pool(dev, size, dma_handle, > - gfp, attrs); > + dma_direct_use_pool(dev, gfp)) { > + page = dma_direct_alloc_from_pool(dev, size, > + dma_handle, &cpu_addr, > + gfp, attrs); > + return page ? cpu_addr : NULL; > + } > > if (is_swiotlb_for_alloc(dev)) { > page = dma_direct_alloc_swiotlb(dev, size, attrs); > @@ -445,7 +448,7 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size, > > if ((attrs & DMA_ATTR_CC_SHARED) && dma_direct_use_pool(dev, gfp)) > return dma_direct_alloc_from_pool(dev, size, dma_handle, > - gfp, attrs); > + &cpu_addr, gfp, attrs); > > if (is_swiotlb_for_alloc(dev)) { > page = dma_direct_alloc_swiotlb(dev, size, attrs);