Messages in this thread | ![/](/images/icornerl.gif) | | From | "Tian, Kevin" <> | Subject | RE: [PATCH v7 03/11] iommu/vt-d: Add custom allocator for IOASID | Date | Fri, 25 Oct 2019 15:52:39 +0000 |
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> From: Lu Baolu [mailto:baolu.lu@linux.intel.com] > Sent: Friday, October 25, 2019 10:39 PM > > Hi, > > On 10/25/19 2:40 PM, Tian, Kevin wrote: > >>>> ioasid_register_allocator(&iommu->pasid_allocator); > >>>> + if (ret) { > >>>> + pr_warn("Custom PASID allocator > >>>> registeration failed\n"); > >>>> + /* > >>>> + * Disable scalable mode on this > >>>> IOMMU if there > >>>> + * is no custom allocator. Mixing > >>>> SM capable vIOMMU > >>>> + * and non-SM vIOMMU are not > >>>> supported. > >>>> + */ > >>>> + intel_iommu_sm = 0; > >>> It's insufficient to disable scalable mode by only clearing > >>> intel_iommu_sm. The DMA_RTADDR_SMT bit in root entry has already > >> been > >>> set. Probably, you need to > >>> > >>> for each iommu > >>> clear DMA_RTADDR_SMT in root entry > >>> > >>> Alternatively, since vSVA is the only customer of this custom PASID > >>> allocator, is it possible to only disable SVA here? > >>> > >> Yeah, I think disable SVA is better. We can still do gIOVA in SM. I > >> guess we need to introduce a flag for sva_enabled. > > I'm not sure whether tying above logic to SVA is the right approach. > > If vcmd interface doesn't work, the whole SM mode doesn't make > > sense which is based on PASID-granular protection (SVA is only one > > usage atop). If the only remaining usage of SM is to map gIOVA using > > reserved PASID#0, then why not disabling SM and just fallback to > > legacy mode? > > > > Based on that I prefer to disabling the SM mode completely (better > > through an interface), and move the logic out of CONFIG_INTEL_ > > IOMMU_SVM > > > > Unfortunately, it is dangerous to disable SM after boot. SM uses > different root/device contexts and pasid table formats. Disabling SM > after boot requires changing above from SM format into legacy format.
You are correct.
> > Since ioasid registration failure is a rare case. How about moving this > part of code up to the early stage of intel_iommu_init() and returning > error if hardware present vcmd capability but software fails to register > a custom ioasid allocator? >
It makes sense to me.
Thanks Kevin
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