Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

[Yi Liu]

On 2023/11/21 13:19, Nicolin Chen wrote:
> On Tue, Nov 21, 2023 at 01:02:49PM +0800, Baolu Lu wrote:
> > On 11/17/23 9:07 PM, Yi Liu wrote:
> > > In nested translation, the stage-1 page table is user-managed but cached
> > > by the IOMMU hardware, so an update on present page table entries in the
> > > stage-1 page table should be followed with a cache invalidation.
> > >
> > > Add an IOMMU_HWPT_INVALIDATE ioctl to support such a cache invalidation.
> > > It takes hwpt_id to specify the iommu_domain, and a multi-entry array to
> > > support multiple invalidation requests in one ioctl.
> > >
> > > Check cache_invalidate_user op in the iommufd_hw_pagetable_alloc_nested,
> > > since all nested domains need that.
> > >
> > > Co-developed-by: Nicolin Chen<nicolinc@xxxxxxxxxx>
> > > Signed-off-by: Nicolin Chen<nicolinc@xxxxxxxxxx>
> > > Signed-off-by: Yi Liu<yi.l.liu@xxxxxxxxx>
> > > ---
> > >    drivers/iommu/iommufd/hw_pagetable.c    | 35 +++++++++++++++++++++++++
> > >    drivers/iommu/iommufd/iommufd_private.h |  9 +++++++
> > >    drivers/iommu/iommufd/main.c            |  3 +++
> > >    include/uapi/linux/iommufd.h            | 35 +++++++++++++++++++++++++
> > >    4 files changed, 82 insertions(+)
> > >
> > > diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> > > index 2abbeafdbd22..367459d92f69 100644
> > > --- a/drivers/iommu/iommufd/hw_pagetable.c
> > > +++ b/drivers/iommu/iommufd/hw_pagetable.c
> > > @@ -238,6 +238,11 @@ iommufd_hwpt_nested_alloc(struct iommufd_ctx *ictx,
> > >                rc = -EINVAL;
> > >                goto out_abort;
> > >        }
> > > +     /* 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;
> > > +     }
> > >        return hwpt_nested;
> >
> > The WARN message here may cause kernel regression when users bisect
> > issues. Till this patch, there are no drivers support the
> > cache_invalidation_user callback yet.
>
> Ah, this is an unintended consequence from our uAPI bisect to
> merge the nesting alloc first...
>
> Would removing the WARN_ON_ONCE be okay? Although having this
> WARN is actually the point here...

seems like we may need to remove it. how about your opinion, @Jason?

> Thanks
> Nic

--
Regards,
Yi Liu