linux-kernel - Re: [PATCH v4 14/14] iommu/arm-smmu-v3: Report events that belong to devices attached to vIOMMU

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Message-ID: <Z3wk9TvmUhB3/zlk@Asurada-Nvidia>
Date: Mon, 6 Jan 2025 10:46:13 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
CC: <jgg@...dia.com>, <kevin.tian@...el.com>, <corbet@....net>,
	<will@...nel.org>, <joro@...tes.org>, <suravee.suthikulpanit@....com>,
	<robin.murphy@....com>, <dwmw2@...radead.org>, <shuah@...nel.org>,
	<linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kselftest@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <eric.auger@...hat.com>,
	<jean-philippe@...aro.org>, <mdf@...nel.org>, <mshavit@...gle.com>,
	<shameerali.kolothum.thodi@...wei.com>, <smostafa@...gle.com>,
	<ddutile@...hat.com>, <yi.l.liu@...el.com>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v4 14/14] iommu/arm-smmu-v3: Report events that belong to
 devices attached to vIOMMU

On Mon, Jan 06, 2025 at 11:01:32AM +0800, Baolu Lu wrote:
> On 1/4/25 03:43, Nicolin Chen wrote:
> > diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
> > index 0a08aa82e7cc..55e3d5a14cca 100644
> > --- a/include/uapi/linux/iommufd.h
> > +++ b/include/uapi/linux/iommufd.h
> > @@ -1016,9 +1016,24 @@ struct iommu_ioas_change_process {
> >   /**
> >    * enum iommu_veventq_type - Virtual Event Queue Type
> >    * @IOMMU_VEVENTQ_TYPE_DEFAULT: Reserved for future use
> > + * @IOMMU_VEVENTQ_TYPE_ARM_SMMUV3: ARM SMMUv3 Virtual Event Queue
> >    */
> >   enum iommu_veventq_type {
> >   	IOMMU_VEVENTQ_TYPE_DEFAULT = 0,
> > +	IOMMU_VEVENTQ_TYPE_ARM_SMMUV3 = 1,
> > +};
> > +
> > +/**
> > + * struct iommu_vevent_arm_smmuv3 - ARM SMMUv3 Virtual Event
> > + *                                  (IOMMU_VEVENTQ_TYPE_ARM_SMMUV3)
> > + * @evt: 256-bit ARM SMMUv3 Event record, little-endian.
> > + *       (Refer to "7.3 Event records" in SMMUv3 HW Spec)
> > + *
> > + * StreamID field reports a virtual device ID. To receive a virtual event for a
> > + * device, a vDEVICE must be allocated via IOMMU_VDEVICE_ALLOC.
> > + */
> > +struct iommu_vevent_arm_smmuv3 {
> > +	__aligned_le64 evt[4];
> >   };
> 
> Nit: I think it would be more readable to add a check in the vevent
> reporting helper.
> 
> diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c
> index 77c34f8791ef..ccada0ada5ff 100644
> --- a/drivers/iommu/iommufd/driver.c
> +++ b/drivers/iommu/iommufd/driver.c
> @@ -86,6 +86,9 @@ int iommufd_viommu_report_event(struct iommufd_viommu
> *viommu,
>         if (WARN_ON_ONCE(!data_len || !event_data))
>                 return -EINVAL;
> 
> +       if (WARN_ON_ONCE(type != IOMMU_VEVENTQ_TYPE_ARM_SMMUV3))
> +               return -EINVAL;
> +

Hmm, that's a good point I think.

>         down_read(&viommu->veventqs_rwsem);
> 
>         veventq = iommufd_viommu_find_veventq(viommu, type);
		    ^
		    |
We actually have been missing a type validation entirely, so the
type could have been rejected by this function. Perhaps we should
add a static list of supported types to struct iommufd_viommu_ops
for drivers to report so that then the core could reject from the
first place during a vEVENTQ allocation.

> Or perhaps the compiler could automatically make a warning if the @type
> is not one of those values in enum iommu_veventq_type?

Just gave that a try. Mine doesn't give any warning. Not sure if
needs to be some "-W" augment though..

> Others look good to me.

Thanks for the review!

Nicolin