linux-kernel - Re: [PATCH v4 10/17] iommufd: Support IOMMU_HWPT

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Message-ID: <ZS2Eisb94o3inW7V@Asurada-Nvidia>
Date:   Mon, 16 Oct 2023 11:44:26 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Yi Liu <yi.l.liu@...el.com>, <joro@...tes.org>,
        <alex.williamson@...hat.com>, <kevin.tian@...el.com>,
        <robin.murphy@....com>, <baolu.lu@...ux.intel.com>,
        <cohuck@...hat.com>, <eric.auger@...hat.com>,
        <kvm@...r.kernel.org>, <mjrosato@...ux.ibm.com>,
        <chao.p.peng@...ux.intel.com>, <yi.y.sun@...ux.intel.com>,
        <peterx@...hat.com>, <jasowang@...hat.com>,
        <shameerali.kolothum.thodi@...wei.com>, <lulu@...hat.com>,
        <suravee.suthikulpanit@....com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        <zhenzhong.duan@...el.com>, <joao.m.martins@...cle.com>
Subject: Re: [PATCH v4 10/17] iommufd: Support IOMMU_HWPT_ALLOC allocation
 with user data

On Mon, Oct 16, 2023 at 08:59:07AM -0300, Jason Gunthorpe wrote:
> On Mon, Oct 16, 2023 at 03:03:04PM +0800, Yi Liu wrote:
> > Current nesting series actually extends HWPT_ALLOC ioctl to accept user
> > data for allocating domain with vendor specific data. Nested translation
> > happens to be the usage of it. But nesting requires invalidation. If we
> > want to do further split, then this new series would be just "extending
> > HWPT_ALLOC to accept vendor specific data from userspace". But it will
> > lack of a user if nesting is separated. Is this acceptable? @Jason
> 
> I'd still like to include the nesting allocation and attach parts
> though, even if they are not usable without invalidation ..

This is the latest series that I reworked (in bottom-up order):
 iommu: Add a pair of helper to copy struct iommu_user_data{_array}
 iommufd: Add IOMMU_HWPT_INVALIDATE
 iommufd: Add a nested HW pagetable object
 iommufd: Share iommufd_hwpt_alloc with IOMMUFD_OBJ_HWPT_NESTED
 iommufd: Derive iommufd_hwpt_paging from iommufd_hw_pagetable
 iommufd: Rename IOMMUFD_OBJ_HW_PAGETABLE to IOMMUFD_OBJ_HWPT_PAGING
 iommufd/device: Add helpers to enforce/remove device reserved regions
 iommu: Add IOMMU_DOMAIN_NESTED and cache_invalidate_user op
 iommu: Pass in parent domain with user_data to domain_alloc_user op

Perhaps we can have a preparatory series to merge first:
 iommufd: Share iommufd_hwpt_alloc with IOMMUFD_OBJ_HWPT_NESTED
 iommufd: Derive iommufd_hwpt_paging from iommufd_hw_pagetable
 iommufd: Rename IOMMUFD_OBJ_HW_PAGETABLE to IOMMUFD_OBJ_HWPT_PAGING
 iommufd/device: Add helpers to enforce/remove device reserved regions

Then next cycle would be basically 4 patches + selftests:
 iommufd: Add IOMMU_HWPT_INVALIDATE
 iommufd: Add a nested HW pagetable object
 iommu: Add IOMMU_DOMAIN_NESTED and cache_invalidate_user op
 iommu: Pass in parent domain with user_data to domain_alloc_user op

The preparatory series doesn't involve functional changes yet have
a good amount of pieces to simplify the "nested HW pagetable" that
is basically nested_alloc/abort/destroy.

> > BTW. Do we still have unsolved issue on the invalidation path?
> 
> I'm not sure, there were so many different versions of it we need to
> go back over it and check the dirver implementations again

Only this v4 has the latest array-based invalidation design. And
it should be straightforward for drivers to define entry/request
structures. It might be a bit rush to review/finalize it at the
stage of rc6 though.

Thanks
Nic