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
