Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH v7 03/11] iommu/vt-d: Add custom allocator for IOASID | From | Lu Baolu <> | Date | Fri, 25 Oct 2019 22:39:23 +0800 |
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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.
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?
Best regards, baolu
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