[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way
>>> On 07.12.17 at 14:52, <julien.grall@xxxxxxxxxx> wrote: > On 06/12/17 17:49, George Dunlap wrote: >> Do you want to reset the p2m multiple times? I thought the goal was >> simply to keep the amount of p2m space you need to flush to a minimum; >> if you expect the memory which has been faulted in by the *last* flush >> to be relatively small, you could just always flush all memory that had >> been touched to that point. >> >> If you *do* need to go through the p2m multiple times, then >> misconfiguration is a much better option than PoD. In PoD, once a page >> has data on it, it can't be removed from the p2m anymore. For the >> misconfiguration technique, you can go through and misconfigure the >> entries in the top-level p2m table as many times as you want. The whole >> reason for doing it on x86 is that it's a relatively lightweight >> operation: we use it to modify MMIO mappings, to enable or disable >> logdirty for migrate, &c. > > Does this also work when you share the page-tables with the IOMMU? It > just occurred to me that for both PoD and "misconfigured bits" we would > get into trouble because page-tables are shared with the IOMMU. PoD and IOMMU are incompatible on x86 at present. The bits we use for "mis-configuring" entries are ignored by the IOMMU, which is not a problem since all we use this approach for (right now) is to update the memory type (i.e. cacheability) for possibly huge ranges. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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