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 mattev@meta.com --- 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;
- vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); + if (priv->attrs == VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_WC) + vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot); + else + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
/* See comments in vfio_pci_core_mmap() re VM_ALLOW_ANY_UNCACHED. */ @@ -343,6 +346,12 @@ static int validate_dmabuf_input(struct vfio_device_feature_dma_buf *dma_buf, size_t length = 0; u32 i;
+ if ((dma_buf->flags != 0) && + ((dma_buf->flags & ~VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_MASK) || + ((dma_buf->flags & VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_MASK) != + VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_WC))) + return -EINVAL; + for (i = 0; i < dma_buf->nr_ranges; i++) { u64 offset = dma_ranges[i].offset; u64 len = 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;
- if (!get_dma_buf.nr_ranges || get_dma_buf.flags) + if (!get_dma_buf.nr_ranges) return -EINVAL;
/* @@ -429,6 +438,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags, priv->vdev = vdev; priv->nr_ranges = get_dma_buf.nr_ranges; priv->size = length; + priv->attrs = get_dma_buf.flags & VFIO_DEVICE_FEATURE_DMA_BUF_ATTR_MASK; ret = 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 = vdev; priv->nr_ranges = nr_ranges; priv->size = req_len; + priv->attrs = 0; priv->phys_vec[0].paddr = phys_start + (pgoff << PAGE_SHIFT); priv->phys_vec[0].len = req_len;
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.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; };
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 from. * nr_ranges is the total number of (P2P DMA) ranges that comprise the dmabuf. * - * flags should be 0. + * flags contains: + * - A field for userspace mapping attribute: by default, suitable for regular + * 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); };