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Sat, 16 May 2026 21:30:13 -0700 (PDT) Received: from ryzen ([2601:644:8000:5b5d:7285:c2ff:fe45:8a32]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2bd5cfe47bdsm109726135ad.44.2026.05.16.21.30.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 16 May 2026 21:30:12 -0700 (PDT) From: Rosen Penev To: iommu@lists.linux.dev Cc: Marek Szyprowski , Robin Murphy , linux-kernel@vger.kernel.org (open list) Subject: [PATCH] dma-direct: Clear pages before coherent remap Date: Sat, 16 May 2026 21:29:55 -0700 Message-ID: <20260517042955.2218649-1-rosenp@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Clear pages through their page mapping before creating a coherent remap for dma-direct allocations. Some architectures implement the coherent remap as uncached memory, where the generic memset() path may use cache-only zeroing instructions that are not valid for the returned CPU mapping. Keep the existing memset() for non-remapped allocations, but avoid normal memset() on the remapped coherent allocation path. Assisted-by: Codex:GPT-5.5 Signed-off-by: Rosen Penev --- kernel/dma/direct.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index 583c5922bca2..76f7bf43bd28 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -8,6 +8,7 @@ #include #include #include +#include #include #include #include @@ -104,6 +105,15 @@ static void __dma_direct_free_pages(struct device *dev= , struct page *page, dma_free_contiguous(dev, page, size); } =20 +static void dma_direct_zero_pages(struct page *page, size_t size) +{ + unsigned long count =3D PAGE_ALIGN(size) >> PAGE_SHIFT; + unsigned long i; + + for (i =3D 0; i < count; i++) + clear_highpage(page + i); +} + static struct page *dma_direct_alloc_swiotlb(struct device *dev, size_t si= ze) { struct page *page =3D swiotlb_alloc(dev, size); @@ -268,6 +278,13 @@ void *dma_direct_alloc(struct device *dev, size_t size, if (remap) { pgprot_t prot =3D dma_pgprot(dev, PAGE_KERNEL, attrs); =20 + /* + * Zero via the page mapping before creating a potentially + * uncached remap. Some architectures cannot safely run normal + * memset on uncached memory. + */ + dma_direct_zero_pages(page, size); + if (force_dma_unencrypted(dev)) prot =3D pgprot_decrypted(prot); =20 @@ -283,10 +300,9 @@ void *dma_direct_alloc(struct device *dev, size_t size, ret =3D page_address(page); if (dma_set_decrypted(dev, ret, size)) goto out_leak_pages; + memset(ret, 0, size); } =20 - memset(ret, 0, size); - if (set_uncached) { arch_dma_prep_coherent(page, size); ret =3D arch_dma_set_uncached(ret, size); --=20 2.54.0