Add vfio_pci_dma_buf_find_pfn(), which a VMA fault handler can use to find a PFN.
This supports multi-range DMABUFs, which typically would be used to represent scattered spans but might even represent overlapping or aliasing spans of PFNs.
Because this is intended to be used in vfio_pci_core.c, we also need to expose the struct vfio_pci_dma_buf in the vfio_pci_priv.h header.
Signed-off-by: Matt Evans mattev@meta.com --- drivers/vfio/pci/vfio_pci_dmabuf.c | 124 ++++++++++++++++++++++++++--- drivers/vfio/pci/vfio_pci_priv.h | 19 +++++ 2 files changed, 130 insertions(+), 13 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c index 04478b7415a0..8b6bae56bbf2 100644 --- a/drivers/vfio/pci/vfio_pci_dmabuf.c +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c @@ -9,19 +9,6 @@
MODULE_IMPORT_NS("DMA_BUF");
-struct vfio_pci_dma_buf { - struct dma_buf *dmabuf; - struct vfio_pci_core_device *vdev; - struct list_head dmabufs_elm; - size_t size; - struct phys_vec *phys_vec; - struct p2pdma_provider *provider; - u32 nr_ranges; - struct kref kref; - struct completion comp; - u8 revoked : 1; -}; - static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf, struct dma_buf_attachment *attachment) { @@ -106,6 +93,117 @@ static const struct dma_buf_ops vfio_pci_dmabuf_ops = { .release = vfio_pci_dma_buf_release, };
+int vfio_pci_dma_buf_find_pfn(struct vfio_pci_dma_buf *vpdmabuf, + struct vm_area_struct *vma, + unsigned long address, + unsigned int order, + unsigned long *out_pfn) +{ + /* + * Given a VMA (start, end, pgoffs) and a fault address, + * search the corresponding DMABUF's phys_vec[] to find the + * range representing the address's offset into the VMA, and + * its PFN. + * + * The phys_vec[] ranges represent contiguous spans of VAs + * upwards from the buffer offset 0; the actual PFNs might be + * in any order, overlap/alias, etc. Calculate an offset of + * the desired page given VMA start/pgoff and address, then + * search upwards from 0 to find which span contains it. + * + * On success, a valid PFN for a page sized by 'order' is + * returned into out_pfn. + * + * Failure occurs if: + * - The page would cross the edge of the VMA + * - The page isn't entirely contained within a range + * - We find a range, but the final PFN isn't aligned to the + * requested order. + * + * (Upon failure, the caller is expected to try again with a + * smaller order; the tests above will always succeed for + * order=0 as the limit case.) + * + * It's suboptimal if DMABUFs are created with neigbouring + * ranges that are physically contiguous, since hugepages + * can't straddle range boundaries. (The construction of the + * ranges vector should merge such ranges.) + */ + + const unsigned long pagesize = PAGE_SIZE << order; + unsigned long rounded_page_addr = address & ~(pagesize - 1); + unsigned long rounded_page_end = rounded_page_addr + pagesize; + unsigned long buf_page_offset; + unsigned long buf_offset = 0; + unsigned int i; + + if (rounded_page_addr < vma->vm_start || rounded_page_end > vma->vm_end) { + if (order > 0) + return -EAGAIN; + + /* A fault address outside of the VMA is absurd. */ + WARN(1, "Fault addr 0x%lx outside VMA 0x%lx-0x%lx\n", + address, vma->vm_start, vma->vm_end); + return -EFAULT; + } + + if (unlikely(check_add_overflow(rounded_page_addr - vma->vm_start, + vma->vm_pgoff << PAGE_SHIFT, &buf_page_offset))) + return -EFAULT; + + for (i = 0; i < vpdmabuf->nr_ranges; i++) { + size_t range_len = vpdmabuf->phys_vec[i].len; + phys_addr_t range_start = vpdmabuf->phys_vec[i].paddr; + + /* + * If the current range starts after the page's span, + * this and any future range won't match. Bail early. + */ + if (buf_page_offset + pagesize <= buf_offset) + break; + + if (buf_page_offset >= buf_offset && + buf_page_offset + pagesize <= buf_offset + range_len) { + /* + * The faulting page is wholly contained + * within the span represented by the range. + * Validate PFN alignment for the order: + */ + unsigned long pfn = (range_start >> PAGE_SHIFT) + + ((buf_page_offset - buf_offset) >> PAGE_SHIFT); + + if (IS_ALIGNED(pfn, 1 << order)) { + *out_pfn = pfn; + return 0; + } + /* Retry with smaller order */ + return -EAGAIN; + } + buf_offset += range_len; + } + + /* + * A hugepage straddling a range boundary will fail to match a + * range, but the address will (eventually) match when retried + * with a smaller page. + */ + if (order > 0) + return -EAGAIN; + + /* + * If we get here, the address fell outside of the span + * represented by the (concatenated) ranges. Setup of a + * mapping must ensure that the VMA is <= the total size of + * the ranges, so this should never happen. But, if it does, + * force SIGBUS for the access and warn. + */ + WARN_ONCE(1, "No range for addr 0x%lx, order %d: VMA 0x%lx-0x%lx pgoff 0x%lx, %u ranges, size 0x%zx\n", + address, order, vma->vm_start, vma->vm_end, vma->vm_pgoff, + vpdmabuf->nr_ranges, vpdmabuf->size); + + return -EFAULT; +} + /* * This is a temporary "private interconnect" between VFIO DMABUF and iommufd. * It allows the two co-operating drivers to exchange the physical address of diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h index fca9d0dfac90..317170a5b407 100644 --- a/drivers/vfio/pci/vfio_pci_priv.h +++ b/drivers/vfio/pci/vfio_pci_priv.h @@ -23,6 +23,19 @@ struct vfio_pci_ioeventfd { bool test_mem; };
+struct vfio_pci_dma_buf { + struct dma_buf *dmabuf; + struct vfio_pci_core_device *vdev; + struct list_head dmabufs_elm; + size_t size; + struct phys_vec *phys_vec; + struct p2pdma_provider *provider; + u32 nr_ranges; + struct kref kref; + struct completion comp; + u8 revoked : 1; +}; + bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev); void vfio_pci_intx_unmask(struct vfio_pci_core_device *vdev);
@@ -114,6 +127,12 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev) return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA; }
+int vfio_pci_dma_buf_find_pfn(struct vfio_pci_dma_buf *vpdmabuf, + struct vm_area_struct *vma, + unsigned long address, + unsigned int order, + unsigned long *out_pfn); + #ifdef CONFIG_VFIO_PCI_DMABUF int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags, struct vfio_device_feature_dma_buf __user *arg,