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

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Date:   Tue, 17 Oct 2023 12:32:31 -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 Tue, Oct 17, 2023 at 12:50:11PM -0300, Jason Gunthorpe wrote:
> 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

I can do the split today. Shall we have a domain_alloc_user op
in VT-d driver? Can we accept a core series only? I understood
it's better to have though...

> > > 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?

I think so:
https://lore.kernel.org/linux-iommu/20230921075431.125239-10-yi.l.liu@intel.com/

Thanks
Nicolin