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Thu, 26 Feb 2026 12:22:57 -0800 (PST) Received: from localhost (2620:10d:c085:208::f) by mail.thefacebook.com (2620:10d:c08b:78::2ac9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.35; Thu, 26 Feb 2026 20:22:56 +0000 From: Matt Evans To: Alex Williamson , Leon Romanovsky , Jason Gunthorpe , Alex Mastro , Mahmoud Adam , David Matlack CC: =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= , Sumit Semwal , =?UTF-8?q?Christian=20K=C3=B6nig?= , Kevin Tian , Ankit Agrawal , Pranjal Shrivastava , Alistair Popple , Vivek Kasireddy , , , , , Subject: [RFC PATCH 6/7] vfio/pci: Add mmap() attributes to DMABUF feature Date: Thu, 26 Feb 2026 12:22:02 -0800 Message-ID: <20260226202211.929005-7-mattev@meta.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260226202211.929005-1-mattev@meta.com> References: <20260226202211.929005-1-mattev@meta.com> 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 X-Proofpoint-GUID: tLZAnEt99yhMVR7DzzedwG1Q3dqkNAqK X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjI2MDE4NiBTYWx0ZWRfX15eKNzaG/OmP JFo3cdA2DKdUsgi8aH90lXhs5OMcRD7XzA97n5hdziEdEWmdyrYdnxdK0PJZdQVyzJ/XLBHIMwj qJL6SlcuMCuHgiQ0/TuqPlBY4fFt2hp183lpHN591XieNyxFQfOrTQZ8+6ZoZ/rOddth5U7N/TD FjTA+V8Rp7vXPfToGi40TmaPianF5D9K9vBtl5zVS1KnchMnIX1ghgZwNogwYfFovthbdct58yx BWqCfP0qLO2p+iGbx/xGiHLh3AE/dK5SUka6uin+x+GffqNXNtcWXL+K8U/vrBfwunu3Busiu3Z an0F0I+9k5EPQRFdpk2IubbFH1IP68nTkHva23hF49VRObMu0ZBG2ZvY5bQUFQWxHsdM8MOjE/b zLUgmyACMGwhWlnkCEcgti7VcRXe3sGQGi8Zdnm4esYA0feklcvHPLeDWYfatBi8a4/Nerd0HHb xZeiBGylNYCFg65TbWA== X-Proofpoint-ORIG-GUID: tLZAnEt99yhMVR7DzzedwG1Q3dqkNAqK X-Authority-Analysis: v=2.4 cv=abZsXBot c=1 sm=1 tr=0 ts=69a0aba1 cx=c_pps a=CB4LiSf2rd0gKozIdrpkBw==:117 a=CB4LiSf2rd0gKozIdrpkBw==:17 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=Mpw57Om8IfrbqaoTuvik:22 a=GgsMoib0sEa3-_RKJdDe:22 a=VabnemYjAAAA:8 a=dDaxl782XL0KO6pWJDcA:9 a=gKebqoRLp9LExxC7YDUY:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-26_02,2026-02-26_01,2025-10-01_01 Content-Type: text/plain; charset="utf-8" A new field is reserved in vfio_device_feature_dma_buf.flags to request CPU-facing memory type attributes for mmap()s of the buffer. Add a flag VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_WC, which results in WC PTEs for the DMABUF's BAR region. Signed-off-by: Matt Evans --- drivers/vfio/pci/vfio_pci_dmabuf.c | 18 ++++++++++++++---- include/uapi/linux/vfio.h | 12 +++++++++--- 2 files changed, 23 insertions(+), 7 deletions(-) diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci= _dmabuf.c index af30ca205f31..d66a918e9934 100644 --- a/drivers/vfio/pci/vfio_pci_dmabuf.c +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c @@ -28,6 +28,7 @@ struct vfio_pci_dma_buf { struct dma_buf_phys_vec *phys_vec; struct p2pdma_provider *provider; u32 nr_ranges; + u32 attrs; enum vfio_pci_dma_buf_status status; }; =20 @@ -286,13 +287,15 @@ static int vfio_pci_dma_buf_mmap(struct dma_buf *dmab= uf, struct vm_area_struct * return -EINVAL; =20 vma->vm_private_data =3D priv; - vma->vm_page_prot =3D pgprot_noncached(vma->vm_page_prot); + + if (priv->attrs =3D=3D VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_WC) + vma->vm_page_prot =3D pgprot_writecombine(vma->vm_page_prot); + else + vma->vm_page_prot =3D pgprot_noncached(vma->vm_page_prot); vma->vm_page_prot =3D pgprot_decrypted(vma->vm_page_prot); =20 /* * See comments in vfio_pci_core_mmap() re VM_ALLOW_ANY_UNCACHED. - * - * FIXME: get mapping attributes from dmabuf? */ vm_flags_set(vma, VM_ALLOW_ANY_UNCACHED | VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP); @@ -402,6 +405,12 @@ static int validate_dmabuf_input(struct vfio_device_fe= ature_dma_buf *dma_buf, size_t length =3D 0; u32 i; =20 + if ((dma_buf->flags !=3D 0) && + ((dma_buf->flags & ~VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_MASK) || + ((dma_buf->flags & VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_MASK) !=3D + VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_WC))) + return -EINVAL; + for (i =3D 0; i < dma_buf->nr_ranges; i++) { u64 offset =3D dma_ranges[i].offset; u64 len =3D dma_ranges[i].length; @@ -446,7 +455,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_= device *vdev, u32 flags, if (copy_from_user(&get_dma_buf, arg, sizeof(get_dma_buf))) return -EFAULT; =20 - if (!get_dma_buf.nr_ranges || get_dma_buf.flags) + if (!get_dma_buf.nr_ranges) return -EINVAL; =20 /* @@ -490,6 +499,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_= device *vdev, u32 flags, priv->vdev =3D vdev; priv->nr_ranges =3D get_dma_buf.nr_ranges; priv->size =3D length; + priv->attrs =3D get_dma_buf.flags & VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_MASK; ret =3D vdev->pci_ops->get_dmabuf_phys(vdev, &priv->provider, get_dma_buf.region_index, priv->phys_vec, dma_ranges, diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h index ac2329f24141..9e0fbf333452 100644 --- a/include/uapi/linux/vfio.h +++ b/include/uapi/linux/vfio.h @@ -1487,7 +1487,9 @@ struct vfio_device_feature_bus_master { * etc. offset/length specify a slice of the region to create the dmabuf f= rom. * nr_ranges is the total number of (P2P DMA) ranges that comprise the dma= buf. * - * flags should be 0. + * flags contains: + * - A field for userspace mapping attribute: by default, suitable for reg= ular + * MMIO. Alternate attributes (such as WC) can be selected. * * Return: The fd number on success, -1 and errno is set on failure. */ @@ -1501,8 +1503,12 @@ struct vfio_region_dma_range { struct vfio_device_feature_dma_buf { __u32 region_index; __u32 open_flags; - __u32 flags; - __u32 nr_ranges; + __u32 flags; + /* Flags sub-field reserved for attribute enum */ +#define VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_MASK (0xf << 28) +#define VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_UC (0 << 28) +#define VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_WC (1 << 28) + __u32 nr_ranges; struct vfio_region_dma_range dma_ranges[] __counted_by(nr_ranges); }; =20 --=20 2.47.3