* 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? 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
