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Thu, 12 Mar 2026 11:46:52 -0700 (PDT) Received: from localhost (2620:10d:c085:208::7cb7) by mail.thefacebook.com (2620:10d:c08b:78::c78f) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.35; Thu, 12 Mar 2026 18:46:51 +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 v2 PATCH 09/10] vfio/pci: Add mmap() attributes to DMABUF feature Date: Thu, 12 Mar 2026 11:46:07 -0700 Message-ID: <20260312184613.3710705-10-mattev@meta.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260312184613.3710705-1-mattev@meta.com> References: <20260312184613.3710705-1-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-Authority-Analysis: v=2.4 cv=WKtyn3sR c=1 sm=1 tr=0 ts=69b30a1c cx=c_pps a=CB4LiSf2rd0gKozIdrpkBw==:117 a=CB4LiSf2rd0gKozIdrpkBw==:17 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=7x6HtfJdh03M6CCDgxCd:22 a=JnKecZnUtZousrUlYMGU:22 a=VabnemYjAAAA:8 a=ZZip-zt6qTTd7FoaoeoA:9 a=gKebqoRLp9LExxC7YDUY:22 X-Proofpoint-ORIG-GUID: RFpW0x6_sBMQCOROfH6RjBKGMUM_JHHy X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzEyMDE1MSBTYWx0ZWRfX/r6l02q19NCa Hukc4vvWd5CNLxy6AloCnP4dOLsgPctiR2Fw/lDsGBe6oeEcGk+2q/SSH/0jZLyhsLGh363UkKp tsLATz9toKL8Sl/JfJhfH+ihnRbPDhp2na/SodIeVdIflIuhwRATy6d2uUrKkrW7GtYS3Jwi4SZ OvvOKFCC17LsxfeJjp5pZEPWONdgzVfATXmKuT5NkOLk6Y3eToNtmtCRIqkHb14b1Y7rMrLL8zC Mm/n+HZm7k2NLjWXSDVW1DhxS0hg3FvsSGgvmJzSLPHIwlsalx3wltZmYQ9srJql+Y9nc1/zdHo j6VLGND/SycL8wTKLzTQn9yvfIp0WMWBhHCvo+XxbbSjeBKzSSJl22lcySX2/f1XcS7a6I+GKFe 9Jk0oMG4ofXh6KxB9rhxmGWB5fDbdJsuEOORIGjxKFh6KXuTP0mGXTLEDRl666+TJvG45mfD73V qWJFNzbEavhU5JhZEWQ== X-Proofpoint-GUID: RFpW0x6_sBMQCOROfH6RjBKGMUM_JHHy 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=2026-03-12_02,2026-03-12_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 | 15 +++++++++++++-- drivers/vfio/pci/vfio_pci_priv.h | 1 + include/uapi/linux/vfio.h | 12 +++++++++--- 3 files changed, 23 insertions(+), 5 deletions(-) diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci= _dmabuf.c index 362207cf7e71..ed5b80f6911e 100644 --- a/drivers/vfio/pci/vfio_pci_dmabuf.c +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c @@ -42,7 +42,10 @@ static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf,= struct vm_area_struct * if (req_start + req_len > priv->size) return -EINVAL; =20 - 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. */ @@ -343,6 +346,12 @@ 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; @@ -386,7 +395,7 @@ 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 /* @@ -429,6 +438,7 @@ 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, @@ -488,6 +498,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core= _device *vdev, priv->vdev =3D vdev; priv->nr_ranges =3D nr_ranges; priv->size =3D req_len; + priv->attrs =3D 0; priv->phys_vec[0].paddr =3D phys_start + (pgoff << PAGE_SHIFT); priv->phys_vec[0].len =3D req_len; =20 diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_p= riv.h index c5a9e06bf81a..562de3cc88f4 100644 --- a/drivers/vfio/pci/vfio_pci_priv.h +++ b/drivers/vfio/pci/vfio_pci_priv.h @@ -40,6 +40,7 @@ struct vfio_pci_dma_buf { u32 nr_ranges; struct kref kref; struct completion comp; + u32 attrs; enum vfio_pci_dma_buf_status status; }; =20 diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h index c1b3fa880aa1..fbbe1adea533 100644 --- a/include/uapi/linux/vfio.h +++ b/include/uapi/linux/vfio.h @@ -1521,7 +1521,9 @@ 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. */ @@ -1535,8 +1537,12 @@ 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