linux-kernel - RE: [PATCH v5 5/9] iommufd: Add iommufd fault object

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Date: Mon, 20 May 2024 03:26:50 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, Jason Gunthorpe <jgg@...pe.ca>
CC: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, "Robin
 Murphy" <robin.murphy@....com>, Jean-Philippe Brucker
	<jean-philippe@...aro.org>, Nicolin Chen <nicolinc@...dia.com>, "Liu, Yi L"
	<yi.l.liu@...el.com>, Jacob Pan <jacob.jun.pan@...ux.intel.com>, "Joel
 Granados" <j.granados@...sung.com>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "virtualization@...ts.linux-foundation.org"
	<virtualization@...ts.linux-foundation.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5 5/9] iommufd: Add iommufd fault object

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Monday, May 20, 2024 8:41 AM
> 
> On 5/15/24 3:57 PM, Tian, Kevin wrote:
> >> From: Baolu Lu <baolu.lu@...ux.intel.com>
> >> Sent: Wednesday, May 8, 2024 6:05 PM
> >>
> >> On 2024/5/8 8:11, Jason Gunthorpe wrote:
> >>> On Tue, Apr 30, 2024 at 10:57:06PM +0800, Lu Baolu wrote:
> >>>> diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-
> priv.h
> >>>> index ae65e0b85d69..1a0450a83bd0 100644
> >>>> --- a/drivers/iommu/iommu-priv.h
> >>>> +++ b/drivers/iommu/iommu-priv.h
> >>>> @@ -36,6 +36,10 @@ struct iommu_attach_handle {
> >>>>    			struct device	*dev;
> >>>>    			refcount_t	users;
> >>>>    		};
> >>>> +		/* attach data for IOMMUFD */
> >>>> +		struct {
> >>>> +			void		*idev;
> >>>> +		};
> >>> We can use a proper type here, just forward declare it.
> >>>
> >>> But this sequence in the other patch:
> >>>
> >>> +       ret = iommu_attach_group(hwpt->domain, idev->igroup->group);
> >>> +       if (ret) {
> >>> +               iommufd_fault_iopf_disable(idev);
> >>> +               return ret;
> >>> +       }
> >>> +
> >>> +       handle = iommu_attach_handle_get(idev->igroup->group,
> >> IOMMU_NO_PASID, 0);
> >>> +       handle->idev = idev;
> >>>
> >>> Is why I was imagining the caller would allocate, because now we have
> >>> the issue that a fault capable domain was installed into the IOMMU
> >>> before it's handle could be fully setup, so we have a race where a
> >>> fault could come in right between those things. Then what happens?
> >>> I suppose we can retry the fault and by the time it comes back the
> >>> race should resolve. A bit ugly I suppose.
> >>
> >> You are right. It makes more sense if the attached data is allocated and
> >> managed by the caller. I will go in this direction and update my series.
> >> I will also consider other review comments you have given in other
> >> places.
> >>
> >
> > Does this direction imply a new iommu_attach_group_handle() helper
> > to pass in the caller-allocated handle pointer or exposing a new
> > iommu_group_set_handle() to set the handle to the group pasid_array
> > and then having iomm_attach_group() to update the domain info in
> > the handle?
> 
> I will add new iommu_attach/replace/detach_group_handle() helpers. Like
> below:
> 
> +/**
> + * iommu_attach_group_handle - Attach an IOMMU domain to an IOMMU
> group
> + * @domain: IOMMU domain to attach
> + * @group: IOMMU group that will be attached
> + * @handle: attach handle
> + *
> + * Returns 0 on success and error code on failure.
> + *
> + * This is a variant of iommu_attach_group(). It allows the caller to
> provide
> + * an attach handle and use it when the domain is attached. This is
> currently
> + * only designed for IOMMUFD to deliver the I/O page faults.
> + */
> +int iommu_attach_group_handle(struct iommu_domain *domain,
> +                             struct iommu_group *group,
> +                             struct iommu_attach_handle *handle)
> 

"currently only designed for IOMMUFD" doesn't sound correct.

design-wise this can be used by anyone which relies on the handle.
There is nothing tied to IOMMUFD.

s/designed for/used by/ is more accurate.