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;
--
2.24.0.432.g9d3f5f5b63-goog
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