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

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Message-ID: <20231017155011.GG3952@nvidia.com>
Date:   Tue, 17 Oct 2023 12:50:11 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Yi Liu <yi.l.liu@...el.com>
Cc:     Nicolin Chen <nicolinc@...dia.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 Tue, Oct 17, 2023 at 04:55:12PM +0800, Yi Liu wrote:
> On 2023/10/17 02:44, Nicolin Chen wrote:
> > 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
> 
> following Jason's comment, it looks like we can just split the cache
> invalidation path out. Then the above looks good after removing
> "iommufd: Add IOMMU_HWPT_INVALIDATE" and also the cache_invalidate_user
> callback in "iommu: Add IOMMU_DOMAIN_NESTED and cache_invalidate_user op".
> Is it? @Jason

If it can make sense, sure. It would be nice to be finished with the
alloc path

> > 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.
> 
> yes, before v4, the cache invalidation path is simple and vendor
> drivers have their own handling.

Have driver implementations of v4 been done to look at?

Jason