> From: Matt Evans <[email protected]>
> Sent: Wednesday, June 10, 2026 11:43 PM
>
> +int vfio_pci_dma_buf_find_pfn(struct vfio_pci_dma_buf *priv,
> + 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
s/neigbouring/neighboring/
> + * ranges that are physically contiguous, since hugepages
> + * can't straddle range boundaries. (The construction of the
> + * ranges vector should merge such ranges.)
though the field is called 'phys_vec', removing 'vector' in description
is clearer here.
> + *
> + * Finally, vma_pgoff_adjust is used for a DMABUF representing
> + * a VFIO BAR mmap, which is created from the start of the
> + * offset region.
Elaborate it a little bit that the vm_pgoff is already counted in paddr
of phys_vec so it should be skipped when finding the pfn.
> + */
> +
> + 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(address,
> pagesize);
> + unsigned long rounded_page_end = rounded_page_addr + pagesize;
> + unsigned long page_buf_offset;
> + unsigned long page_buf_offset_end;
what about "fault_offset[_end]"? page_buf is a bit confusing.
> + unsigned long range_buf_offset = 0;
could this be called 'range_start' then the 'range_start' in latter loop
is renamed to 'phys_start'?
Not strong... just feel such naming helps me understand the logic easier
> + 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;
> + }
> +
> + /*
> + * page_buff_offset[_end] is the span of DMABUF offsets
> + * corresponding to the faulting page:
> + */
if the naming is kept then s/page_buff_offset/page_buf_offset/
otherwise,
Reviewed-by: Kevin Tian <[email protected]>
