Re: [PATCH v6 13/14] iommu/arm-smmu-v3: Report events that belong to devices attached to vIOMMU

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Feb 20, 2025 at 07:24:07PM -0400, Jason Gunthorpe wrote:
> On Thu, Feb 20, 2025 at 12:45:46PM -0800, Nicolin Chen wrote:
> > ------------------------------------------------------------
> > diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
> > index fd2f13a63f27..be9746ecdc65 100644
> > --- a/include/uapi/linux/iommufd.h
> > +++ b/include/uapi/linux/iommufd.h
> > @@ -1067,7 +1067,16 @@ enum iommu_veventq_type {
> >   * 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)
> > + *       Reported event records: (Refer to "7.3 Event records" in SMMUv3 HW Spec)
> > + *       - 0x02 C_BAD_STREAMID
> 
> This is documented as 'Transaction StreamID out of range.' so it would
> by a hypervisor kernel bug to hit it

I see. Dropping it.

> > + *       - 0x04 C_BAD_STE
> 
> I'm not sure we do enough validation to reject all bad STE fragments
> so it makes sense this could happen.
> 
> > + *       - 0x06 F_STREAM_DISABLED
> 
> This looked guest triggerable to me.. so it makes sense

Keeping these two.

> > + *       - 0x08 C_BAD_SUBSTREAMID
> > + *       - 0x0a C_BAD_STE
> 
> Typo, this is C_BAD_CD

Fixed.

> > But F_CD_FETCH and F_STE_FETCH seem to be complicated here, as both
> 
> F_STE_FETCH would indicate a hypervisor failure managing the stream
> table so no need to forward it.
> 
> > report PA in their FetchAddr fields, although the spec does mention
> > both might be injected to a guest VM:
> >  - "Note: This event might be injected into a guest VM, as though
> >     from a virtual SMMU, when a hypervisor receives a stage 2
> >     Translation-related fault indicating CD fetch as a cause (with
> >     CLASS == CD)."
> 
> That sounds like the VMM should be catching the
> F_TRANSLATION and convert it for the CLASS=CD
> 
> > For F_CD_FETCH, at least the CD table pointer in the nested STE is
> > an IPA, and all the entries in the CD table that can be 2-level are
> > IPAs as well. So, we need some kinda reverse translation from a PA
> > to IPA using its stage-2 mapping. I am not sure what's the best way
> > to do that...
> 
> And if the F_TRANSLATION covers the case then maybe this just stays in
> the hypervisor?

> > Otherwise, perhaps not-supporting them in this series might be a
> > safer bet?
> 
> Yeah, I would consider skipping F_CD_FETCH. May also just try it out
> and see what events come out on a CD fetch failure..

I will skip these two for now. Meanwhile, will try some hack to
trigger a FETCH fault.

Thanks
Nicolin