On 25.07.2019 12:54, Roger Pau Monné wrote: > On Thu, Jul 25, 2019 at 10:22:17AM +0000, Jan Beulich wrote: >> On 23.07.2019 17:48, Roger Pau Monne wrote: >>> Current code only prevent mapping the lapic page into the guest >>> physical memory map. Expand the range to be 0xFEEx_xxxx as described >>> in the Intel VTd specification section 3.13 "Handling Requests to >>> Interrupt Address Range". >>> >>> AMD also lists this address range in the AMD SR5690 Databook, section >>> 2.4.4 "MSI Interrupt Handling and MSI to HT Interrupt Conversion". >>> >>> Requested-by: Andrew Cooper <andrew.coop...@citrix.com> >>> Signed-off-by: Roger Pau Monné <roger....@citrix.com> >> >> I've committed this on the basis that it shouldn't hurt, but having >> thought about this some more I'm not really sure I see the point: >> The IOMMU special cases accesses into this range anyway, to redirect >> lookup to the interrupt remapping table instead of the DMA remapping >> one. Hence any mappings inserted into this range are simply useless, >> but shouldn't otherwise hurt. > > Intel SDM contains: > > "Software must ensure the second-level paging-structure entries are > programmed not to remap input addresses to the interrupt address > range. Hardware behavior is undefined for memory requests remapped to > the interrupt address range." > > In section 3.13 (Handling Requests to Interrupt Address Range). > > Since arch_iommu_hwdom_init/hwdom_iommu_map adds entries to both the > hap and the iommu page tables (or to hap only if shared) Xen should be > careful to not map this range because the iommu special cases this > range, but I'm not sure what hap does.
Hmm, in the shared-pt case this is indeed desirable in any event. I have to admit that I didn't recall that even in the non-shared case arch_iommu_hwdom_init() would fiddle with the HAP tables as well, rather than just the IOMMU ones. I don't think this should remain this way long term. Or was there a reason for this to be needed? Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
