On Fri, 5 Jan 2018 22:38:39 +0100 Alexander Boettcher (AB) wrote: > > I am not following the recent development of all those kernels, so I > > think it's best to directly consult the individual developers/teams for > > statements (like the one from Stefan above). > > > > For my part, I can tell you that the NOVA microhypervisor (at least the > > official version) does not map physical RAM into the kernel virtual address > > space, other than the RAM in which microhypervisor itself resides. NOVA maps > > certain devices (like APIC, IOMMU), but those can't be speculatively > > accessed anyway. I cannot comment on modified NOVA versions. > > I for my part, can confirm that the slightly, cough, modified NOVA > version [1], as used by Genode, kept the original behavior of the > official NOVA version [0] in that regard.
An addition after looking at the old code some more: Note that Pd::kern, i.e. the kernel PD, actually has all physical memory mapped 1:1, simply to have an elegant (non-special-case) way to establish the root of the mapping hierarchy. However, no user thread ever runs in Pd::kern, so those mappings cannot be speculatively abused. In PDs, where user threads do run, physical memory is not mapped in the page tables. Cheers, Udo
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