Re: [PATCH 09/17] iommufd: Add kernel-managed hw_pagetable allocation for userspace

Jason Gunthorpe
2023-02-09T20:45:15Z

On Wed, Feb 08, 2023 at 08:31:45PM -0800, Yi Liu wrote:
> Today iommufd allocates the kernel-managed hw_pagetabe implicitly when
> device is attached to an IOAS. This links the hw_pagetable to IOPT within
> IOAS.
>
> However, this is not the perfect way. It makes much sense to let userspace
> explicitly request hw_pagtable allocation via iommufd. The reason is even
> though the hw_pagetable is kernel-managed, the mappings are feed by
> userspace. Also, this makes the lifecircle of kernel-managed hw_pagetable
> more clear during usage. This is very important in the usage of nested
> translation, in which the kernel-managed hw_pagetable would be used as the
> stage-2 hw_pagetable. In such case, both stage-1 and stage-2 hw_pagetable
> should be allocated by userspace to ensure the life-circle.
>
> This adds an ioctl IOMMU_HWPT_ALLOC for the hw_pagetable allocation. For
> kernel-managed hw_pagetable, userspace should provide an IOAS ID in the
> allocation request.
>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
> drivers/iommu/iommufd/device.c | 11 ++-
> drivers/iommu/iommufd/hw_pagetable.c | 116 ++++++++++++++++++++++++
> drivers/iommu/iommufd/iommufd_private.h | 15 +++
> drivers/iommu/iommufd/main.c | 3 +
> include/uapi/linux/iommufd.h | 48 ++++++++++
> 5 files changed, 191 insertions(+), 2 deletions(-)

This patch and its requirements should all be first in the series. A
mini series who's only job is to add IOMMU_HWPT_ALLOC

Then patches to add IOMMU_HWPT_INVALIDATE

Then the vt-d implementation of all this, including the vt-d specific
changes to the uapi/etc.

Jason