Messages in this thread | | | Date | Thu, 17 Aug 2023 13:28:39 -0300 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v2] iommu/arm-smmu-v3: Allow default substream bypass with a pasid support |
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On Thu, Aug 17, 2023 at 05:24:51PM +0100, Robin Murphy wrote: > > > @@ -2435,6 +2440,16 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev) > > > } else if (smmu_domain->smmu != smmu) > > > ret = -EINVAL; > > > + /* > > > + * When attaching an IDENTITY domain to a master with pasid capability, > > > + * the master can still enable SVA feature by allocating a multi-entry > > > + * CD table and attaching the IDENTITY domain to its default substream > > > + * that alone can be byassed using the S1DSS field of the STE. > > > + */ > > > + if (smmu_domain->stage == ARM_SMMU_DOMAIN_BYPASS && master->ssid_bits && > > > + smmu->features & ARM_SMMU_FEAT_TRANS_S1) > > > + smmu_domain->stage = ARM_SMMU_DOMAIN_BYPASS_S1DSS; > > > > Then you don't technically need to do this. > > > > Though if we can't atomically change the STE from IDENTITY to IDENTIY > > with a CD then you still have to do something here, > > Strictly I think we are safe to do that - fill in all the S1* fields while > Config[0] is still 0 and they're ignored, sync, then set Config[0]. Adding a > CD table under a translation domain should be achievable as well, since > S1CDMax, S1ContextPtr and S1Fmt can all be updated together atomically > (although it's still the kind of switcheroo where I'd be scared of a massive > boulder suddenly rolling out of the ceiling...)
That sounds pretty good then we don't have to force staying in CD mode
> > but really what we > > want is to force a CD table for all cases if PASID is enabled, and > > force DMA domains to be S2 domains as well. > > Wut? No, DMA domains really want to be stage 1, for many reasons. > Implementing them with stage 2 when stage 1 isn't supported was always a bit > of a bodge, but thankfully I'm not aware of anyone ever building a > stage-2-only SMMUv3 anyway. > > The most glaringly obvious one, though, is that I think people like PASID > support and SVA to actually work ;)
Blah, I keep doing this and swapping S1/S2 in this confusing naming scheme (and it doesn't help that AMD is backwards, sigh) - I ment what you said :)
Thanks, Jason
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