* Dr. David Alan Gilbert (dgilbert@xxxxxxxxxx) wrote: > * Cornelia Huck (cohuck@xxxxxxxxxx) wrote: > > This series makes it possible to enable MTE for kvm guests, if the kernel > > supports it. Again, tested on the simulator via patiently waiting for the > > arm64/mte kselftests to finish successfully. > > > > For tcg, turning on mte on the machine level (to get tag memory) stays a > > requirement. If the new mte cpu feature is not explicitly specified, a tcg > > vm will get mte depending on the presence of tag memory (just as today). > > > > For kvm, mte stays off by default; this is because migration is not yet > > supported (postcopy will need an extension of the kernel interface, possibly > > an extension of the userfaultfd interface), and turning on mte will add a > > migration blocker. > > My assumption was that a normal migration would need something as well > to retrieve and place the MTE flags; albeit not atomically. > > > My biggest question going forward is actually concerning migration; I gather > > that we should not bother adding something unless postcopy is working as well? > > I don't think that restriction is fair on you; just make sure > postcopy_ram_supported_by_host gains an arch call and fails cleanly; > that way if anyone tries to enable postcopy they'll find out with a > clean fail. > > > If I'm not misunderstanding things, we need a way to fault in a page together > > with the tag; doing that in one go is probably the only way that we can be > > sure that this is race-free on the QEMU side. Comments welcome :) > > I think it will. > But, ignoring postcopy for a minute, with KVM how do different types of > backing memory work - e.g. if I back a region of guest memory with > /dev/shm/something or a hugepage equivalent, where does the MTE memory > come from, and how do you set it? Another case that just came to mind, are the data content optimisations; we special case all-zero pages, which I guess you still need to transmit tags for, and the xbzrle page-difference code wouldn't notice differences in tags. Dave > Dave > > > Changes v1->v2: [Thanks to Eric for the feedback!] > > - add documentation > > - switch the mte prop to OnOffAuto; this improves the interaction with the > > existing mte machine prop > > - leave mte off for kvm by default > > - improve tests; the poking in QDicts feels a bit ugly, but seems to work > > > > Cornelia Huck (2): > > arm/kvm: add support for MTE > > qtests/arm: add some mte tests > > > > docs/system/arm/cpu-features.rst | 21 +++++ > > target/arm/cpu.c | 18 ++--- > > target/arm/cpu.h | 1 + > > target/arm/cpu64.c | 132 +++++++++++++++++++++++++++++++ > > target/arm/internals.h | 1 + > > target/arm/kvm64.c | 5 ++ > > target/arm/kvm_arm.h | 12 +++ > > target/arm/monitor.c | 1 + > > tests/qtest/arm-cpu-features.c | 77 ++++++++++++++++++ > > 9 files changed, 256 insertions(+), 12 deletions(-) > > > > -- > > 2.35.3 > > > -- > Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK
