Messages in this thread | | | Date | Mon, 28 Oct 2019 15:49:00 -0700 | From | Jacob Pan <> | Subject | Re: [PATCH v7 03/11] iommu/vt-d: Add custom allocator for IOASID |
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On Fri, 25 Oct 2019 15:52:39 +0000 "Tian, Kevin" <kevin.tian@intel.com> wrote:
> > 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. > sounds good to me too, the earlier the less to clean up. > Thanks > Kevin
[Jacob Pan]
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