Re: [PATCH v4 17/21] iommu/riscv: Report cache coherency capability

[Jason Gunthorpe]

On Thu, Aug 20, 2026 at 11:41:46PM +0200, Andrew Jones wrote:
> VFIO and iommufd require IOMMU_CAP_CACHE_COHERENCY because they use
> IOMMU_CACHE mappings and have no userspace cache-maintenance path.
> 
> RISC-V page tables preserve physical memory attributes for IOMMU_CACHE
> mappings. Svpbmt marks mappings without IOMMU_CACHE as non-cacheable,
> but preserving physical attributes cannot make a noncoherent device
> path coherent.
> 
> Report the capability only for devices marked DMA coherent. This limits
> userspace assignment to paths that can honor cacheable mappings.
> 
> Signed-off-by: Andrew Jones <andrew.jones@xxxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/riscv/iommu.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

You can send this outside this series?

Jason