On Fri, 2011-11-11 at 15:49 -0700, Alex Williamson wrote: > To fix this, switch domain_update_iommu_coherency() to use the > safer, non-coherent default for domains not attached to iommus. That isn't a fix for the problem you described. The problem is that changing a domain from coherent to non-coherent is *broken*. It probably needs to flush the cache for the *entire* set of page tables — not just the new context entry it adds. You might have removed the *common* case where we trigger that bug, but it certainly isn't a fix. However, I'd be receptive to an argument that the situation you describe is in fact the *only* time we'd have to switch from coherent to non-coherent at run time, because the coherency is an all-or-nothing characteristic of the chipset. Either all the IOMMUs are coherent, or none of them, right? This brain-damage only affects the first chipsets from before we worked out that cache incoherency was a *really* f*cking stupid idea, doesn't it? So if you were to ditch the whole idea of a per-domain runtime update, and instead calculate a global value for 'iommu_coherency' at boot time, by iterating over for_each_active_iommu()¹, I think that would be a better way to deal with the issue. And you *could* really call that a 'fix'. Make sense? -- dwmw2 ¹ just in *case* they ever differ
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