Hi Akihiko,
> Subject: Re: [PATCH v8 09/10] virtio-gpu-dmabuf: Improve error
> handling with 'Error **' and err enum
> >> On 2026/02/28 7:13, Vivek Kasireddy wrote:
> >>> Make the error handling more robust in virtio_gpu_init_udmabuf()
> >>> by introducing 'Error **' parameter to capture errors and using an
> >>> enum from VFIO to categorize Guest and Host errors. This allows
> >>> for better error reporting and handling of errors from
> >>> virtio_gpu_create_udmabuf() and virtio_gpu_remap_dmabuf().
> >>>
> >>> 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 | 61 ++++++++++++++++++++++++-
> ------
> >> ---
> >>> 1 file changed, 43 insertions(+), 18 deletions(-)
> >>>
> >>> diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-
> >> dmabuf.c
> >>> index 8d67ef7c2a..b2badfc1bd 100644
> >>> --- a/hw/display/virtio-gpu-dmabuf.c
> >>> +++ b/hw/display/virtio-gpu-dmabuf.c
> >>> @@ -18,6 +18,7 @@
> >>> #include "ui/console.h"
> >>> #include "hw/virtio/virtio-gpu.h"
> >>> #include "hw/virtio/virtio-gpu-pixman.h"
> >>> +#include "hw/vfio/vfio-device.h"
> >>> #include "trace.h"
> >>> #include "system/ramblock.h"
> >>> #include "system/hostmem.h"
> >>> @@ -27,16 +28,18 @@
> >>> #include "standard-headers/linux/udmabuf.h"
> >>> #include "standard-headers/drm/drm_fourcc.h"
> >>>
> >>> -static void virtio_gpu_create_udmabuf(struct
> >> virtio_gpu_simple_resource *res)
> >>> +static int virtio_gpu_create_udmabuf(struct
> >> virtio_gpu_simple_resource *res,
> >>> + Error **errp)
> >>> {
> >>> g_autofree struct udmabuf_create_list *list = NULL;
> >>> RAMBlock *rb;
> >>> ram_addr_t offset;
> >>> - int udmabuf, i;
> >>> + int udmabuf, i, fd;
> >>>
> >>> udmabuf = udmabuf_fd();
> >>> if (udmabuf < 0) {
> >>> - return;
> >>> + error_setg(errp, "udmabuf device not available or enabled");
> >>> + return VFIO_DMABUF_CREATE_HOST_ERROR;
> >>
> >> I failed to point out one thing for naming of the enum. The name
> should
> >> express if the error is caused by invalid iov or something else. Then
> >> virtio-gpu decides how to recover the error; it's virtio-gpu who knows
> >> the iov is from the guest and decides to report a guest error, not
> vfio.
> >> Otherwise, it reports a host error.
> > So, it sounds like you are suggesting that there needs to be three
> enum
> > values:
> > enum {
> > /* Guest is responsible for this error */
> > VFIO_DMABUF_CREATE_GUEST_ERROR = -1,
> > /* Guest is at fault as the IOVEC passed in is invalid */
> > VFIO_DMABUF_CREATE_INVALID_IOV_ERROR = -2,
> > /* Host is at fault for this error */
> > VFIO_DMABUF_CREATE_HOST_ERROR = -3,
> > }
>
> vfio doesn't know if the guest or the host is responsible, so it cannot
> make use of VFIO_DMABUF_CREATE_GUEST_ERROR and
> VFIO_DMABUF_CREATE_HOST_ERROR.
>
> >
> > Or, please let me know in detail what changes you would like to see.
>
> A possible combination of values is as follows:
>
> - VFIO_DMABUF_CREATE_ERR_UNSPEC
> - VFIO_DMABUF_CREATE_ERR_INVALID_IOV
Just these two error types are needed? Should I completely drop
VFIO_DMABUF_CREATE_GUEST_ERROR and VFIO_DMABUF_CREATE_HOST_ERROR,
even for udmabuf errors?
Thanks,
Vivek
>
> I took the example of VIRTIO_GPU_RESP_ERR_UNSPEC and
> VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER for naming.
>
> >
> >>
> >>> }
> >>>
> >>> list = g_malloc0(sizeof(struct udmabuf_create_list) +
> >>> @@ -45,7 +48,8 @@ static void virtio_gpu_create_udmabuf(struct
> >> virtio_gpu_simple_resource *res)
> >>> for (i = 0; i < res->iov_cnt; i++) {
> >>> rb = qemu_ram_block_from_host(res->iov[i].iov_base, false,
> >> &offset);
> >>> if (!rb || rb->fd < 0) {
> >>> - return;
> >>> + error_setg(errp, "IOV memory address incompatible with
> >> udmabuf ");
> >>> + return VFIO_DMABUF_CREATE_GUEST_ERROR;
> >>> }
> >>>
> >>> list->list[i].memfd = rb->fd;
> >>> @@ -56,22 +60,30 @@ static void
> virtio_gpu_create_udmabuf(struct
> >> virtio_gpu_simple_resource *res)
> >>> list->count = res->iov_cnt;
> >>> list->flags = UDMABUF_FLAGS_CLOEXEC;
> >>>
> >>> - res->dmabuf_fd = ioctl(udmabuf, UDMABUF_CREATE_LIST, list);
> >>> - if (res->dmabuf_fd < 0) {
> >>> - warn_report("%s: UDMABUF_CREATE_LIST: %s", __func__,
> >>> - strerror(errno));
> >>> + fd = ioctl(udmabuf, UDMABUF_CREATE_LIST, list);
> >>> + if (fd < 0) {
> >>> + error_setg_errno(errp, errno, "UDMABUF_CREATE_LIST: ioctl
> >> failed");
> >>> + if (errno == EINVAL || errno == EBADFD) {
> >>> + return VFIO_DMABUF_CREATE_GUEST_ERROR;
> >>> + }
> >>> + return VFIO_DMABUF_CREATE_HOST_ERROR;
> >>> }
> >>> + return fd;
> >>> }
> >>>
> >>> -static void virtio_gpu_remap_dmabuf(struct
> >> virtio_gpu_simple_resource *res)
> >>> +static bool virtio_gpu_remap_dmabuf(struct
> >> virtio_gpu_simple_resource *res,
> >>> + Error **errp)
> >>> {
> >>> - res->remapped = mmap(NULL, res->blob_size, PROT_READ,
> >>> - MAP_SHARED, res->dmabuf_fd, 0);
> >>> - if (res->remapped == MAP_FAILED) {
> >>> - warn_report("%s: dmabuf mmap failed: %s", __func__,
> >>> - strerror(errno));
> >>> + void *map;
> >>> +
> >>> + map = mmap(NULL, res->blob_size, PROT_READ, MAP_SHARED,
> res-
> >>> dmabuf_fd, 0);
> >>> + if (map == MAP_FAILED) {
> >>> + error_setg_errno(errp, errno, "dmabuf mmap failed");
> >>> res->remapped = NULL;
> >>> + return false;
> >>> }
> >>> + res->remapped = map;
> >>> + return true;
> >>> }
> >>>
> >>> static void virtio_gpu_destroy_dmabuf(struct
> >> virtio_gpu_simple_resource *res)
> >>> @@ -125,19 +137,32 @@ bool virtio_gpu_have_udmabuf(void)
> >>>
> >>> void virtio_gpu_init_dmabuf(struct virtio_gpu_simple_resource
> *res)
> >>> {
> >>> + Error *local_err = NULL;
> >>> void *pdata = NULL;
> >>> + int ret;
> >>>
> >>> res->dmabuf_fd = -1;
> >>> if (res->iov_cnt == 1 &&
> >>> res->iov[0].iov_len < 4096) {
> >>> pdata = res->iov[0].iov_base;
> >>> } else {
> >>> - virtio_gpu_create_udmabuf(res);
> >>> - if (res->dmabuf_fd < 0) {
> >>> + ret = virtio_gpu_create_udmabuf(res, &local_err);
> >>> + if (ret < 0) {
> >>> + error_prepend(&local_err, "Cannot create dmabuf: ");
> >>
> >> This error_prepend() is redundant. The error messages
> >> virtio_gpu_create_udmabuf() emits already suggests they are
> problems
> >> with DMA-BUF.
> > Ok, I'll drop the error_prepend().
> >
> > Thanks,
> > Vivek
> >
> >>
> >> Regards,
> >> Akihiko Odaki
> >>
> >>> +
> >>> + if (ret == VFIO_DMABUF_CREATE_GUEST_ERROR) {
> >>> + qemu_log_mask(LOG_GUEST_ERROR,
> >>> + "Cannot create dmabuf: incompatible
> memory\n");
> >>> + error_free(local_err);
> >>> + return;
> >>> + }
> >>> + error_report_err(local_err);
> >>> return;
> >>> }
> >>> - virtio_gpu_remap_dmabuf(res);
> >>> - if (!res->remapped) {
> >>> +
> >>> + res->dmabuf_fd = ret;
> >>> + if (!virtio_gpu_remap_dmabuf(res, &local_err)) {
> >>> + error_report_err(local_err);
> >>> return;
> >>> }
> >>> pdata = res->remapped;
> >
