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a="76867927" X-IronPort-AV: E=Sophos;i="6.23,113,1770624000"; d="scan'208";a="76867927" X-CSE-ConnectionGUID: ytok5TbrRUmGmDlnGMP1cw== X-CSE-MsgGUID: 1OMY7PnMTTOYKimVFTanLg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,113,1770624000"; d="scan'208";a="215611453" From: Vivek Kasireddy To: qemu-devel@nongnu.org Cc: Vivek Kasireddy , Alex Williamson , =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= Subject: [PATCH v11 08/10] vfio/device: Add a helper to mmap a dmabuf Date: Tue, 10 Mar 2026 19:50:50 -0700 Message-ID: <20260311025340.1335673-9-vivek.kasireddy@intel.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260311025340.1335673-1-vivek.kasireddy@intel.com> References: <20260311025340.1335673-1-vivek.kasireddy@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=192.198.163.13; envelope-from=vivek.kasireddy@intel.com; helo=mgamail.intel.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.819, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.903, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @intel.com) X-ZM-MESSAGEID: 1773197859131154100 In order to mmap a dmabuf, we first need to create a placeholder mapping that would fit the entire size of the dmabuf. This mapping would then be replaced with smaller mappings of individual dmabuf segments. Cc: Alex Williamson Cc: C=C3=A9dric Le Goater Signed-off-by: Vivek Kasireddy --- hw/vfio/device.c | 64 +++++++++++++++++++++++++++++++++++ hw/vfio/dmabuf-stubs.c | 7 ++++ include/hw/vfio/vfio-device.h | 16 +++++++++ 3 files changed, 87 insertions(+) diff --git a/hw/vfio/device.c b/hw/vfio/device.c index 2d01059be0..fdb94f1457 100644 --- a/hw/vfio/device.c +++ b/hw/vfio/device.c @@ -725,3 +725,67 @@ int vfio_device_create_dmabuf_fd(struct iovec *iov, un= signed int iov_cnt, } return ret; } + +void *vfio_device_mmap_dmabuf(struct iovec *iov, unsigned int iov_cnt, + size_t total_size, Error **errp) +{ + struct vfio_region_info *info =3D NULL; + VFIODevice *vbasedev =3D NULL; + ram_addr_t offset, len =3D 0; + RAMBlock *first_rb, *rb; + void *map, *submap; + int i, index; + + if (!vfio_device_lookup(iov, &vbasedev, errp)) { + return NULL; + } + + /* + * We first reserve a contiguous chunk of address space for the entire + * dmabuf, then replace it with smaller mappings that correspond to the + * individual segments of the dmabuf. + */ + map =3D mmap(NULL, total_size, PROT_NONE, MAP_SHARED | MAP_ANONYMOUS, = -1, 0); + if (map =3D=3D MAP_FAILED) { + error_setg_errno(errp, errno, "Could not reserve placeholder mappi= ng"); + return NULL; + } + + for (i =3D 0; i < iov_cnt; i++) { + rb =3D qemu_ram_block_from_host(iov[i].iov_base, false, &offset); + if (i =3D=3D 0) { + first_rb =3D rb; + } + if (!rb || rb !=3D first_rb) { + error_setg(errp, "Cannot mmap dmabuf with different regions\n"= ); + goto err; + } + + index =3D vfio_get_region_index_from_mr(rb->mr); + if (index < 0) { + error_setg(errp, "Cannot find region index for dmabuf segment\= n"); + goto err; + } + + if (vfio_device_get_region_info(vbasedev, index, &info)) { + error_setg(errp, "Cannot find region info for dmabuf segment\n= "); + goto err; + } + + submap =3D mmap(map + len, iov[i].iov_len, PROT_READ, + MAP_SHARED | MAP_FIXED, vbasedev->fd, + info->offset + offset); + if (submap =3D=3D MAP_FAILED) { + error_setg_errno(errp, errno, "Could not mmap dmabuf segment\n= "); + goto err; + } + + len +=3D iov[i].iov_len; + } + return map; +err: + munmap(map, total_size); + error_prepend(errp, "VFIO dmabuf mmap failed: "); + return NULL; +} + diff --git a/hw/vfio/dmabuf-stubs.c b/hw/vfio/dmabuf-stubs.c index e71e2b68dd..92b52bc60d 100644 --- a/hw/vfio/dmabuf-stubs.c +++ b/hw/vfio/dmabuf-stubs.c @@ -15,3 +15,10 @@ int vfio_device_create_dmabuf_fd(struct iovec *iov, unsi= gned int iov_cnt, error_setg(errp, "VFIO dmabuf support is not enabled"); return VFIO_DMABUF_CREATE_HOST_ERROR; } + +void *vfio_device_mmap_dmabuf(struct iovec *iov, unsigned int iov_cnt, + size_t total_size, Error **errp) +{ + error_setg(errp, "VFIO mmap dmabuf support is not enabled"); + return NULL; +} diff --git a/include/hw/vfio/vfio-device.h b/include/hw/vfio/vfio-device.h index 566e5d8bc0..60783d6fd5 100644 --- a/include/hw/vfio/vfio-device.h +++ b/include/hw/vfio/vfio-device.h @@ -340,6 +340,22 @@ int vfio_get_region_index_from_mr(MemoryRegion *mr); */ int vfio_device_create_dmabuf_fd(struct iovec *iov, unsigned int iov_cnt, Error **errp); + +/** + * Mmap a dmabuf by first translating the addresses in the iovec + * array into VFIO region offsets and then creating a placeholder + * mapping that would be replaced later with mappings that + * correspond to the dmabuf segments. + * + * @iov: array of iovec entries associated with the dmabuf + * @iov_cnt: number of entries in the iovec array + * @total_size: total size of the dmabuf + * @errp: pointer to Error*, to store an error if it happens. + * + * Returns the mapped pointer on success and NULL on error. + */ +void *vfio_device_mmap_dmabuf(struct iovec *iov, unsigned int iov_cnt, + size_t total_size, Error **errp); #endif =20 /* Returns 0 on success, or a negative errno. */ --=20 2.53.0