Re: [libvirt PATCH 0/5] Add bus-lock-ratelimit
On Thu, Dec 02, 2021 at 06:01:03PM +0100, Tim Wiederhake wrote:
This was introduced recently in QEMU, see
https://bugzilla.redhat.com/show_bug.cgi?id=1982165:
Bus locks disrupts overall performance since it blocks all other cores
(which must wait for the bus lock to be released before their memory
operations).
For VMM, it can detect every bus lock acquired by guest VMs and induces
a VM exit. So VMM can count the number/frequency of bus lock and take
some throttling action or just kill the guest.
NB this feedback is not directed at you, but rather the
requester of this feature.
This request is awful as it exists today. The bugs and upstream
commit provide little to no information for apps or libvirt to
make sensible decisions on.
We shouldn't expose this in libvirt until someone can explain
sensible usage policy for applications and why QEMU isn't just
setting a sensible value in the machine type by default, given
this is claimed to be an important guest denial of service
mitigation..
Regards,
Daniel
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