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

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Message-ID: <ZSnmId5g2m/UnxKY@Asurada-Nvidia>
Date:   Fri, 13 Oct 2023 17:51:45 -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 Fri, Oct 13, 2023 at 09:07:09PM -0300, Jason Gunthorpe wrote:
> On Fri, Oct 13, 2023 at 01:58:59PM -0700, Nicolin Chen wrote:
> > On Fri, Oct 13, 2023 at 12:19:23PM -0300, Jason Gunthorpe wrote:
> > > On Thu, Sep 21, 2023 at 12:51:31AM -0700, Yi Liu wrote:
> > > > IOMMU_HWPT_ALLOC already supports iommu_domain allocation for usersapce.
> > > > But it can only allocate a hw_pagetable that associates to a given IOAS,
> > > > i.e. only a kernel-managed hw_pagetable of IOMMU_HWPT_TYPE_DEFAULT type.
> > > > 
> > > > IOMMU drivers can now support user-managed hw_pagetables, for two-stage
> > > > translation use cases, that require user data input from the user space.
> > > > 
> > > > Extend the IOMMU_HWPT_ALLOC ioctl to accept non-default hwpt_type with a
> > > > type specified user data. Also, update the @pt_id to accept hwpt_id too
> > > > besides an ioas_id. Then, pass them to the downstream alloc_fn().
> > > > 
> > > > Co-developed-by: Nicolin Chen <nicolinc@...dia.com>
> > > > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > > > Signed-off-by: Yi Liu <yi.l.liu@...el.com>
> > > > ---
> > > >  drivers/iommu/iommufd/hw_pagetable.c | 19 ++++++++++++++++++-
> > > >  include/uapi/linux/iommufd.h         | 23 +++++++++++++++++++++--
> > > >  2 files changed, 39 insertions(+), 3 deletions(-)
> > > 
> > > Can we also come with a small vt-d patch that does implement an op for
> > > this? Or is it too big?
> > > 
> > > It would be nice if we could wrap IOMMU_HWPT_ALLOC into one
> > > self-contained series and another series for invalidate.
> > 
> > We now only use IOMMU_HWPT_ALLOC for nested domain allocations,
> > which won't be supported until the cache_invalidate_user ops is
> > preset?
> > 
> > /* e.g. the following piece is in iommufd_user_managed_hwpt_alloc */
> > 
> > +       /* Driver is buggy by missing cache_invalidate_user in domain_ops */
> > +       if (WARN_ON_ONCE(!hwpt->domain->ops->cache_invalidate_user)) {
> > +               rc = -EINVAL;
> > +               goto out_abort;
> > +       }
> >
> 
> Hm. That hunk could migrate to the invalidate series. 
> 
> I'm just leeary of doing the invalidation too considering how
> complicated it is

OK. Let's see how Yi/Kevin/Baolu reply about the feasibility
with the VT-d driver. Then Yi and I can accordingly separate
the allocation part into a smaller series.

Thanks
Nic