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Jan Beulich
a94d697376
The initial if() was inverted, invalidating all output from this function. Which in turn means the mirroring of P2M mappings into the IOMMU didn't always work as intended: Mappings may have got updated when there was no need to. There would not have been too few (un)mappings; what saves us is that alongside the flags comparison MFNs also get compared, with non-present entries always having an MFN of 0 or INVALID_MFN while present entries always have MFNs different from these two (0 in the table also meant to cover INVALID_MFN): OLD NEW P W access MFN P W access MFN 0 0 r 0 0 0 n 0 0 1 rw 0 0 1 n 0 1 0 n non-0 1 0 r non-0 1 1 n non-0 1 1 rw non-0 present <-> non-present transitions are fine because the MFNs differ. present -> present transitions as well as non-present -> non-present ones are potentially causing too many map/unmap operations, but never too few, because in that case old (bogus) and new access differ. Fixes:d1bb6c97c3("IOMMU: also pass p2m_access_t to p2m_get_iommu_flags()) Signed-off-by: Jan Beulich <jbeulich@suse.com> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com> master commit:e70a9a043amaster date: 2021-09-07 14:24:49 +0200