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The VMM simply maps something from a > device and cannot probe the cacheability KVM is mirroring the MM's PTEs to the S2's PTEs. You can think about this differently - KVM currently has a little bug where the MM's PTE's can say cachable but KVM will mirror it to a S2 PTE that is forced non-cachable. KVM will not do any cache flushing to make this safe. Fundamentally that discrepancy is what is being addressed here. Cachable PTEs in the MM should be mirrored to cachable PTEs in the S2. That the issue only arises with non-struct page memory is just part of the triggering condition.. > I assume with the cacheable pfn mapping, the whole range covered by the > vma is entirely safe to be mapped as such in user space. Yes Jason