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 matt@ozlabs.org --- drivers/vfio/pci/vfio_pci_dmabuf.c | 153 ++++++++++++++++++++++++++--- drivers/vfio/pci/vfio_pci_priv.h | 20 ++++ 2 files changed, 160 insertions(+), 13 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c index c16f460c01d6..7c047400dfd1 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 +93,146 @@ 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 *priv, + struct vm_area_struct *vma, + unsigned long fault_addr, + 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: + * - A hugepage would cross the edge of the VMA, + * - A hugepage isn't entirely contained within a range + * (including where it straddles the boundary between + * ranges), + * - We find a range, but the final PFN isn't aligned to the + * requested order. + * + * Upon failure, -EAGAIN is returned and the caller is + * expected to try again with a smaller order, which will + * eventually succeed (order=0 will always work). + * + * It's suboptimal if DMABUFs are created with neighbouring + * ranges that are physically contiguous, since hugepages + * can't straddle range boundaries. (The construction of the + * ranges should merge them in this case.) + * + * Finally, vma_pgoff_adjust is used with a DMABUF created for + * a VFIO BAR mmap: a BAR mapped with vm_pgoff > 0 creates a + * DMABUF such that byte 0 of the VMA corresponds to byte 0 of + * the DMABUF and byte 'vm_pgoff << PAGE_SHIFT' into the BAR. + * To avoid double-offsetting in this scenario, subtracting + * vma_pgoff_adjust from this (non-zero) vm_pgoff generates + * the effective offset. + */ + + const unsigned long pagesize = PAGE_SIZE << order; + unsigned long vma_off = ((vma->vm_pgoff - priv->vma_pgoff_adjust) << + PAGE_SHIFT) & VFIO_PCI_OFFSET_MASK; + unsigned long rounded_page_addr = ALIGN_DOWN(fault_addr, pagesize); + unsigned long rounded_page_end = rounded_page_addr + pagesize; + unsigned long fault_offset; + unsigned long fault_offset_end; + unsigned long range_start_offset = 0; + unsigned int i; + int ret; + + 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. */ + dev_warn_ratelimited( + &priv->vdev->pdev->dev, + "Fault addr 0x%lx outside VMA 0x%lx-0x%lx\n", + fault_addr, vma->vm_start, vma->vm_end); + return -EFAULT; + } + + /* + * fault_offset[_end] is the span within the DMABUF + * corresponding to the faulting page: + */ + if (unlikely(check_add_overflow(rounded_page_addr - vma->vm_start, + vma_off, &fault_offset) || + check_add_overflow(fault_offset, pagesize, + &fault_offset_end))) + return -EFAULT; + + /* + * Iterate over ranges in the buffer, summing their lengths: + * range_start_offset represents the current range's starting + * offset in the buffer (from 0 upwards). + * + * A failure for order == 0 is unexpected, and triggers a + * fault/warn. + */ + ret = (order == 0) ? -EFAULT : -EAGAIN; + + for (i = 0; i < priv->nr_ranges; i++) { + size_t range_len = priv->phys_vec[i].len; + + /* Early exit if range starts after the page end */ + if (fault_offset_end <= range_start_offset) + break; + + if (fault_offset >= range_start_offset && + fault_offset_end <= range_start_offset + range_len) { + /* + * The faulting page is wholly contained + * within the span represented by this range, + * so validate PFN alignment for the order. + * The if() condition ensures the pfn + * arithmetic won't overflow. + */ + unsigned long pfn = + ((fault_offset - range_start_offset) + + priv->phys_vec[i].paddr) >> PAGE_SHIFT; + + if (IS_ALIGNED(pfn, 1 << order)) { + *out_pfn = pfn; + ret = 0; + } + /* + * Else order > 0; EAGAIN retries with smaller + * order + */ + break; + } + range_start_offset += range_len; + } + + if (order == 0 && ret != 0) + /* + * The address fell outside of the span represented by + * the (concatenated) ranges. As setup of a mapping + * ensures that the VMA is <= the total size of the + * ranges this should never happen. If it does, warn + * and SIGBUS. + */ + dev_warn_ratelimited( + &priv->vdev->pdev->dev, + "No range for addr 0x%lx, order %d: VMA 0x%lx-0x%lx pgoff 0x%lx, %u ranges, size 0x%zx\n", + fault_addr, order, vma->vm_start, vma->vm_end, + vma->vm_pgoff, priv->nr_ranges, priv->size); + + return ret; +} + /* * 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..c8f6f959056a 100644 --- a/drivers/vfio/pci/vfio_pci_priv.h +++ b/drivers/vfio/pci/vfio_pci_priv.h @@ -23,6 +23,20 @@ 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; + unsigned long vma_pgoff_adjust; + 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 +128,12 @@ 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,