In order to create a dmabuf associated with a buffer that spans multiple ranges, we first need to identify the VFIO region and index the buffer (represented by iovec) belongs to and then translate its addresses to offsets within that region.
The qemu_ram_block_from_host() API gives us both the region and the offset info we need to populate the dma ranges so that we can invoke the VFIO_DEVICE_FEATURE_DMA_BUF feature to create the dmabuf. Also, instead of iterating over all QOM devices to find the VFIODevice associated with a memory region, introduce a helper to just use the vfio_device_list to lookup the VFIODevice. And, introduce another helper to lookup the VFIO region given an address. Lastly, introduce an enum to return the type of error encountered while creating the dmabuf fd. Cc: Alex Williamson <[email protected]> Cc: Cédric Le Goater <[email protected]> Signed-off-by: Vivek Kasireddy <[email protected]> --- include/hw/vfio/vfio-device.h | 22 +++++++ hw/vfio/device.c | 109 ++++++++++++++++++++++++++++++++++ hw/vfio/dmabuf-stubs.c | 17 ++++++ hw/vfio/meson.build | 1 + 4 files changed, 149 insertions(+) create mode 100644 hw/vfio/dmabuf-stubs.c diff --git a/include/hw/vfio/vfio-device.h b/include/hw/vfio/vfio-device.h index 8472420d3f..c05430be8a 100644 --- a/include/hw/vfio/vfio-device.h +++ b/include/hw/vfio/vfio-device.h @@ -41,6 +41,13 @@ enum { VFIO_DEVICE_TYPE_AP = 3, }; +enum { + /* The Guest passed addresses stored in IOV are invalid */ + VFIO_DMABUF_CREATE_ERR_INVALID_IOV = -1, + /* Guest or Host may be at fault for this type of error */ + VFIO_DMABUF_CREATE_ERR_UNSPEC = -2, +}; + typedef struct VFIODeviceOps VFIODeviceOps; typedef struct VFIODeviceIOOps VFIODeviceIOOps; typedef struct VFIOMigration VFIOMigration; @@ -323,6 +330,21 @@ bool vfio_device_has_region_cap(VFIODevice *vbasedev, int region, uint16_t cap_t int vfio_device_get_irq_info(VFIODevice *vbasedev, int index, struct vfio_irq_info *info); + +/** + * Create a dmabuf fd by first translating the addresses in the + * iovec array into VFIO region offsets and then invoking the + * VFIO_DEVICE_FEATURE_DMA_BUF feature. + * + * @iov: array of iovec entries associated with a buffer + * @iov_cnt: number of entries in the iovec array + * @errp: pointer to Error*, to store an error if it happens. + * + * Returns the created dmabuf fd or either VFIO_DMABUF_CREATE_ERR_UNSPEC + * or VFIO_DMABUF_CREATE_ERR_INVALID_IOV on error. + */ +int vfio_device_create_dmabuf_fd(struct iovec *iov, unsigned int iov_cnt, + Error **errp); #endif /* Returns 0 on success, or a negative errno. */ diff --git a/hw/vfio/device.c b/hw/vfio/device.c index 4f11959633..d95503a5f1 100644 --- a/hw/vfio/device.c +++ b/hw/vfio/device.c @@ -21,7 +21,9 @@ #include "qemu/osdep.h" #include <sys/ioctl.h> +#include "system/ramblock.h" #include "hw/vfio/vfio-device.h" +#include "hw/vfio/vfio-region.h" #include "hw/vfio/pci.h" #include "hw/core/iommu.h" #include "trace.h" @@ -667,3 +669,110 @@ static VFIODeviceIOOps vfio_device_io_ops_ioctl = { .region_read = vfio_device_io_region_read, .region_write = vfio_device_io_region_write, }; + +/* + * This helper looks up the VFIODevice corresponding to the given iov. It + * can be useful to determinine if a buffer (represented by the iov) belongs + * to a VFIO device or not. This is mainly invoked when external components + * such as virtio-gpu request creation of dmabuf fds for buffers that may + * belong to a VFIO device. + */ +static bool vfio_device_lookup(struct iovec *iov, VFIODevice **vbasedevp, + RAMBlock **first_rbp, Error **errp) +{ + VFIODevice *vbasedev; + RAMBlock *first_rb; + ram_addr_t offset; + + first_rb = qemu_ram_block_from_host(iov[0].iov_base, false, &offset); + if (!first_rb) { + error_setg(errp, "Could not find first ramblock\n"); + return false; + } + + *first_rbp = first_rb; + QLIST_FOREACH(vbasedev, &vfio_device_list, next) { + if (vbasedev->dev == first_rb->mr->dev) { + *vbasedevp = vbasedev; + return true; + } + } + error_setg(errp, "No VFIO device found to create dmabuf from\n"); + return false; +} + +/* + * This helper looks up the VFIORegion corresponding to the given address. + * It also verifies that the RAMBlock associated with the address is the + * same as the first_rb passed in. This is to ensure that all addresses + * in the iov belong to the same region. + */ +static bool vfio_region_lookup(void *addr, VFIORegion **regionp, + RAMBlock *first_rb, ram_addr_t *offsetp, + Error **errp) +{ + VFIORegion *region; + RAMBlock *rb; + + rb = qemu_ram_block_from_host(addr, false, offsetp); + if (!rb || rb != first_rb) { + error_setg(errp, "Dmabuf segments must belong to the same region\n"); + return false; + } + + region = vfio_get_region_from_mr(rb->mr); + if (region) { + *regionp = region; + return true; + } + error_setg(errp, "Could not find valid region for dmabuf segment\n"); + return false; +} + +int vfio_device_create_dmabuf_fd(struct iovec *iov, unsigned int iov_cnt, + Error **errp) +{ + g_autofree struct vfio_device_feature *feature = NULL; + struct vfio_device_feature_dma_buf *dma_buf; + RAMBlock *first_rb = NULL; + VFIODevice *vbasedev; + VFIORegion *region; + ram_addr_t offset; + size_t argsz; + int i, ret; + + if (!vfio_device_lookup(iov, &vbasedev, &first_rb, errp)) { + return VFIO_DMABUF_CREATE_ERR_INVALID_IOV; + } + + argsz = sizeof(*feature) + sizeof (*dma_buf) + + sizeof(struct vfio_region_dma_range) * iov_cnt; + feature = g_malloc0(argsz); + *feature = (struct vfio_device_feature) { + .argsz = argsz, + .flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_DMA_BUF, + }; + dma_buf = (struct vfio_device_feature_dma_buf *)feature->data; + + for (i = 0; i < iov_cnt; i++) { + if (!vfio_region_lookup(iov[i].iov_base, ®ion, + first_rb, &offset, errp)) { + return VFIO_DMABUF_CREATE_ERR_INVALID_IOV; + } + + dma_buf->region_index = region->nr; + dma_buf->dma_ranges[i].offset = offset; + dma_buf->dma_ranges[i].length = iov[i].iov_len; + } + + dma_buf->nr_ranges = iov_cnt; + dma_buf->open_flags = O_RDONLY | O_CLOEXEC; + + ret = vfio_device_get_feature(vbasedev, feature); + if (ret < 0) { + error_setg_errno(errp, -ret, + "Could not create dmabuf fd via VFIO device"); + return VFIO_DMABUF_CREATE_ERR_UNSPEC; + } + return ret; +} diff --git a/hw/vfio/dmabuf-stubs.c b/hw/vfio/dmabuf-stubs.c new file mode 100644 index 0000000000..fb5318e929 --- /dev/null +++ b/hw/vfio/dmabuf-stubs.c @@ -0,0 +1,17 @@ +/* + * Copyright (c) 2026 Intel and/or its affiliates. + * + * SPDX-License-Identifier: GPL-2.0-or-later + */ + +#include "qemu/osdep.h" +#include "qemu/error-report.h" +#include "qemu/iov.h" +#include "hw/vfio/vfio-device.h" + +int vfio_device_create_dmabuf_fd(struct iovec *iov, unsigned int iov_cnt, + Error **errp) +{ + error_setg(errp, "VFIO dmabuf support is not enabled"); + return VFIO_DMABUF_CREATE_ERR_UNSPEC; +} diff --git a/hw/vfio/meson.build b/hw/vfio/meson.build index c7c31b78f6..aa6f4bc1b4 100644 --- a/hw/vfio/meson.build +++ b/hw/vfio/meson.build @@ -38,3 +38,4 @@ stub_ss.add(files('iommufd-stubs.c')) system_ss.add(when: 'CONFIG_VFIO_PCI', if_true: files( 'display.c', )) +system_ss.add(when: 'CONFIG_VFIO', if_false: files('dmabuf-stubs.c')) -- 2.53.0
