On 2025/11/12 13:24, Kasireddy, Vivek wrote:
Hi Akihiko,
Subject: Re: [PATCH v2 09/10] virtio-gpu-dmabuf: Introduce
qemu_iovec_same_memory_regions()
On 2025/11/09 14:33, Vivek Kasireddy wrote:
Add a helper to check whether the addresses in an iovec array
belong to the same memory region or not. This is useful to verify
before trying to create a dmabuf from an iovec array.
Cc: Marc-André Lureau <[email protected]>
Cc: Alex Bennée <[email protected]>
Cc: Akihiko Odaki <[email protected]>
Cc: Dmitry Osipenko <[email protected]>
Cc: Alex Williamson <[email protected]>
Cc: Cédric Le Goater <[email protected]>
Signed-off-by: Vivek Kasireddy <[email protected]>
---
hw/display/virtio-gpu-dmabuf.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-
dmabuf.c
index c34d4c85bc..80143034d4 100644
--- a/hw/display/virtio-gpu-dmabuf.c
+++ b/hw/display/virtio-gpu-dmabuf.c
@@ -27,6 +27,31 @@
#include "standard-headers/linux/udmabuf.h"
#include "standard-headers/drm/drm_fourcc.h"
+static bool qemu_iovec_same_memory_regions(const struct iovec *iov,
int iov_cnt)
+{
+ RAMBlock *rb, *curr_rb;
+ ram_addr_t offset;
+ int i;
+
+ rb = qemu_ram_block_from_host(iov[0].iov_base, false, &offset);
+ if (!rb) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: Could not find ramblock/memory region\n", __func__);
+ return false;
+ }
+
+ for (i = 1; i < iov_cnt; i++) {
+ curr_rb = qemu_ram_block_from_host(iov[i].iov_base, false,
&offset);
+ if (curr_rb != rb) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: memory regions not same for iov entries\n",
+ __func__);
+ return false;
+ }
+ }
+ return true;
+}
+
static void virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource
*res)
{
struct udmabuf_create_list *list;
@@ -137,6 +162,10 @@ void virtio_gpu_init_dmabuf(struct
virtio_gpu_simple_resource *res)
res->iov[0].iov_len < 4096) {
pdata = res->iov[0].iov_base;
} else {
+ if (!qemu_iovec_same_memory_regions(res->iov, res->iov_cnt)) {
+ return;
+ }
+
This check is unnecessary. Perhaps rejecting iov with different memory
regions may be fine if that simplifies the code, but this actually adds
some code.
I think we can keep this sanity check but I don't really mind dropping this
patch given that buffers with mixed memory regions are not encountered
in practical situations. Or, I guess I could move the if (curr_rb != rb) check
to virtio_gpu_create_udmabuf() and vfio_device_create_dmabuf_fd()
like you suggested previously.
I won't call it a "sanity check"; it is "unlikely" to have different
memory regions, but it is still not "wrong" and is sane.
The VFIO code path still needs to check if the memory regions belong to
one VFIO device. Trying to create one DMA-BUF using multiple VFIO
devices is wrong.
Regards,
Akihiko Odaki
