The main use for udmabuf is sending guest memory pages to the host.
It's generally a bad idea to have to separate mappings with different attributes. For example, a WC mapping the guest kernel and cached mapping on the host is problematic.
v2: Cache attribute flags instead of read/write flags (kraxel@) --- drivers/dma-buf/udmabuf.c | 12 ++++++++++++ include/uapi/linux/udmabuf.h | 2 ++ 2 files changed, 14 insertions(+)
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index b345e91d831a..ce9caaaa9e4b 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -16,6 +16,7 @@ static const u32 list_limit = 1024; /* udmabuf_create_list->count limit */ static const size_t size_limit_mb = 64; /* total dmabuf size, in megabytes */
struct udmabuf { + u32 flags; pgoff_t pagecount; struct page **pages; }; @@ -37,6 +38,12 @@ static const struct vm_operations_struct udmabuf_vm_ops = { static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma) { struct udmabuf *ubuf = buf->priv; + pgprot_t pgprot = vm_get_page_prot(vma->vm_flags); + + if (ubuf->flags & UDMABUF_FLAGS_WC) + vma->vm_page_prot = pgprot_writecombine(pgprot); + else if (ubuf->flags & UDMABUF_FLAGS_NONCACHED) + vma->vm_page_prot = pgprot_noncached(pgprot);
if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0) return -EINVAL; @@ -132,6 +139,10 @@ static long udmabuf_create(const struct udmabuf_create_list *head, int seals, ret = -EINVAL; u32 i, flags;
+ if ((head->flags & UDMABUF_FLAGS_NONCACHED) && + (head->flags & UDMABUF_FLAGS_WC)) + return -EINVAL; + ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL); if (!ubuf) return -ENOMEM; @@ -188,6 +199,7 @@ static long udmabuf_create(const struct udmabuf_create_list *head, exp_info.priv = ubuf; exp_info.flags = O_RDWR;
+ ubuf->flags = head->flags; buf = dma_buf_export(&exp_info); if (IS_ERR(buf)) { ret = PTR_ERR(buf); diff --git a/include/uapi/linux/udmabuf.h b/include/uapi/linux/udmabuf.h index 46b6532ed855..f90831f2bb0d 100644 --- a/include/uapi/linux/udmabuf.h +++ b/include/uapi/linux/udmabuf.h @@ -6,6 +6,8 @@ #include <linux/ioctl.h>
#define UDMABUF_FLAGS_CLOEXEC 0x01 +#define UDMABUF_FLAGS_WC 0x02 +#define UDMABUF_FLAGS_NONCACHED 0x04
struct udmabuf_create { __u32 memfd;