RE: [PATCH V4 04/10] iommufd: Add an ioctl IOMMU_IOAS_GET_PA to query PA from IOVA

Tian, Kevin
2026-04-16T08:02:44Z

> From: Jacob Pan <jacob.pan@linux.microsoft.com>
> Sent: Wednesday, April 15, 2026 5:14 AM
>
> To support no-IOMMU mode where userspace drivers perform unsafe DMA
> using physical addresses, introduce a new API to retrieve the
> physical address of a user-allocated DMA buffer that has been mapped to
> an IOVA via IOAS. The mapping is backed by mock I/O page tables
> maintained
> by generic IOMMUPT framework.
>
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Jacob Pan <jacob.pan@linux.microsoft.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Your s-o-b should be the last

> + /*
> + * Scan the domain for the contiguous physical address length so that
> + * userspace search can be optimized for fewer ioctls.
> + */
> + while (iova < iopt_area_last_iova(area)) {
> + unsigned long next_iova;
> + u64 next_paddr;
> +
> + if (check_add_overflow(iova, PAGE_SIZE, &next_iova))
> + break;
> +
> + next_paddr = iommu_iova_to_phys(area->storage_domain,
> next_iova);
> +
> + if (!next_paddr || next_paddr != tmp_paddr + PAGE_SIZE)
> + break;

the 2nd condition should be WARN_ON?

> @@ -432,6 +432,7 @@ union ucmd_buffer {
> struct iommu_veventq_alloc veventq;
> struct iommu_vfio_ioas vfio_ioas;
> struct iommu_viommu_alloc viommu;
> + struct iommu_ioas_get_pa get_pa;

alphabetic order

> #ifdef CONFIG_IOMMUFD_TEST
> struct iommu_test_cmd test;
> #endif
> @@ -484,6 +485,8 @@ static const struct iommufd_ioctl_op
> iommufd_ioctl_ops[] = {
> struct iommu_ioas_map_file, iova),
> IOCTL_OP(IOMMU_IOAS_UNMAP, iommufd_ioas_unmap, struct
> iommu_ioas_unmap,
> length),
> + IOCTL_OP(IOMMU_IOAS_GET_PA, iommufd_ioas_get_pa, struct
> iommu_ioas_get_pa,
> + out_phys),

ditto

>
> +/**
> + * struct iommu_ioas_get_pa - ioctl(IOMMU_IOAS_GET_PA)
> + * @size: sizeof(struct iommu_ioas_get_pa)
> + * @flags: Reserved, must be 0 for now
> + * @ioas_id: IOAS ID to query IOVA to PA mapping from
> + * @__reserved: Must be 0
> + * @iova: IOVA to query
> + * @out_length: Number of bytes contiguous physical address starting from
> phys
> + * @out_phys: Output physical address the IOVA maps to
> + *
> + * Query the physical address backing an IOVA range. The entire range must
> be
> + * mapped already. For noiommu devices doing unsafe DMA only.
> + */
> +struct iommu_ioas_get_pa {
> + __u32 size;
> + __u32 flags;
> + __u32 ioas_id;
> + __u32 __reserved;
> + __aligned_u64 iova;
> + __aligned_u64 out_length;
> + __aligned_u64 out_phys;
> +};
> +#define IOMMU_IOAS_GET_PA _IO(IOMMUFD_TYPE,
> IOMMUFD_CMD_IOAS_GET_PA)
> +

Based on its purpose let's make the restriction in the name, e.g.

IOMMUFD_CMD_IOAS_NOIOMMU_GET_PA