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[47.55.120.4]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-88060de9b44sm10817116d6.20.2025.11.03.16.06.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Nov 2025 16:06:19 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vG4Z1-00000006cRs-0csK; Mon, 03 Nov 2025 20:06:19 -0400 Date: Mon, 3 Nov 2025 20:06:19 -0400 From: Jason Gunthorpe To: Alex Mastro Cc: Leon Romanovsky , Bjorn Helgaas , Logan Gunthorpe , Jens Axboe , Robin Murphy , Joerg Roedel , Will Deacon , Marek Szyprowski , Andrew Morton , Jonathan Corbet , Sumit Semwal , Christian =?utf-8?B?S8O2bmln?= , Alex Williamson , Kees Cook , "Gustavo A. R. Silva" , Ankit Agrawal , Yishai Hadas , Shameer Kolothum , Kevin Tian , Krishnakant Jaju , Matt Ochs , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, iommu@lists.linux.dev, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, kvm@vger.kernel.org, linux-hardening@vger.kernel.org, Vivek Kasireddy Subject: Re: [PATCH v6 00/11] vfio/pci: Allow MMIO regions to be exported through dma-buf Message-ID: <20251104000619.GG1204670@ziepe.ca> References: <20251102-dmabuf-vfio-v6-0-d773cff0db9f@nvidia.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Nov 03, 2025 at 12:07:12PM -0800, Alex Mastro wrote: > On Sun, Nov 02, 2025 at 10:00:48AM +0200, Leon Romanovsky wrote: > > Changelog: > > v6: > > * Fixed wrong error check from pcim_p2pdma_init(). > > * Documented pcim_p2pdma_provider() function. > > * Improved commit messages. > > * Added VFIO DMA-BUF selftest. > > * Added __counted_by(nr_ranges) annotation to struct vfio_device_feature_dma_buf. > > * Fixed error unwind when dma_buf_fd() fails. > > * Document latest changes to p2pmem. > > * Removed EXPORT_SYMBOL_GPL from pci_p2pdma_map_type. > > * Moved DMA mapping logic to DMA-BUF. > > * Removed types patch to avoid dependencies between subsystems. > > * Moved vfio_pci_dma_buf_move() in err_undo block. > > * Added nvgrace patch. > > Thanks Leon. Attaching a toy program which sanity tests the dma-buf export UAPI > by feeding the allocated dma-buf into an dma-buf importer (libibverbs + CX-7). Oh! Here is my toy program to do the same with iommufd as the importer: #define _GNU_SOURCE #define __user #include #include #include #include #include #include "include/uapi/linux/vfio.h" #include "include/uapi/linux/iommufd.h" #include #include #include int main(int argc, const char *argv[]) { int vfio_dev_fd, iommufd_fd, ret; // Open the per-device VFIO file (e.g., /dev/vfio/devices/vfio3) vfio_dev_fd = open("/dev/vfio/devices/vfio0", O_RDWR); if (vfio_dev_fd < 0) { perror("Failed to open VFIO per-device file"); return 1; } // Open /dev/iommu for iommufd iommufd_fd = open("/dev/iommu", O_RDWR); if (iommufd_fd < 0) { perror("Failed to open /dev/iommu"); close(vfio_dev_fd); return 1; } // Bind device FD to iommufd struct vfio_device_bind_iommufd bind = { .argsz = sizeof(bind), .flags = 0, .iommufd = iommufd_fd, }; ret = ioctl(vfio_dev_fd, VFIO_DEVICE_BIND_IOMMUFD, &bind); if (ret < 0) { perror("VFIO_DEVICE_BIND_IOMMUFD failed"); close(vfio_dev_fd); close(iommufd_fd); return 1; } // Allocate an IOAS (I/O address space) struct iommu_ioas_alloc alloc_data = { .size = sizeof(alloc_data), .flags = 0, }; ret = ioctl(iommufd_fd, IOMMU_IOAS_ALLOC, &alloc_data); if (ret < 0) { perror("IOMMU_IOAS_ALLOC failed"); close(vfio_dev_fd); close(iommufd_fd); return 1; } // Attach the device to the IOAS struct vfio_device_attach_iommufd_pt attach_data = { .argsz = sizeof(attach_data), .flags = 0, .pt_id = alloc_data.out_ioas_id, }; ret = ioctl(vfio_dev_fd, VFIO_DEVICE_ATTACH_IOMMUFD_PT, &attach_data); if (ret < 0) { perror("VFIO_DEVICE_ATTACH_IOMMUFD_PT failed"); close(vfio_dev_fd); close(iommufd_fd); return 1; } #if 0 int mapfd = memfd_create("test", MFD_CLOEXEC); if (mapfd == -1) { perror("memfd_create failed"); return 1; } ftruncate(mapfd, 4096); #else struct dmabuf_arg { struct vfio_device_feature hdr; struct vfio_device_feature_dma_buf dma_buf; struct vfio_region_dma_range range; } dma_buf_feature = { .hdr = { .argsz = sizeof(dma_buf_feature), .flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_DMA_BUF }, .dma_buf = { .region_index = VFIO_PCI_BAR0_REGION_INDEX, .open_flags = O_CLOEXEC, .nr_ranges = 1 }, .range = { .length = 4096 }, }; ret = ioctl(vfio_dev_fd, VFIO_DEVICE_FEATURE, &dma_buf_feature); if (ret < 0) { perror("VFIO_DEVICE_FEATURE_GET failed"); return 1; } int mapfd = ret; #endif struct iommu_ioas_map_file map_file = { .size = sizeof(map_file), .flags = IOMMU_IOAS_MAP_WRITEABLE | IOMMU_IOAS_MAP_READABLE, .ioas_id = alloc_data.out_ioas_id, .fd = mapfd, .start = 0, .length = 4096, }; ret = ioctl(iommufd_fd, IOMMU_IOAS_MAP_FILE, &map_file); if (ret < 0) { perror("IOMMU_IOAS_MAP_FILE failed"); return 1; } printf("Successfully attached device to IOAS ID: %u\n", alloc_data.out_ioas_id); close(vfio_dev_fd); close(iommufd_fd); return 0; }