Messages in this thread | | | Date | Thu, 20 Jan 2022 16:14:13 +0100 | Subject | Re: [PATCH v2 0/7] kvm: fix latent guest entry/exit bugs | From | Christian Borntraeger <> |
| |
Am 20.01.22 um 13:03 schrieb Mark Rutland: > On Thu, Jan 20, 2022 at 12:28:09PM +0100, Paolo Bonzini wrote: >> On 1/19/22 20:22, Mark Rutland wrote: >>> I wonder, is the s390 guest entry/exit*preemptible* ? >>> >>> If a timer IRQ can preempt in the middle of the EQS, we wouldn't balance >>> things before a ctx-switch to the idle thread, which would then be able >>> to hit this. >>> >>> I'll need to go audit the other architectures for similar. >> >> They don't enable interrupts in the entry/exit path so they should be okay. > > True. > > So it sounds like for s390 adding an explicit preempt_{disable,enable}() is the > right thing to do. I'll add that and explanatory commentary.
That would not be trivial I guess. We do allow (and need) page faults on sie for guest demand paging and
this piece of arch/s390/mm/fault.c
case GMAP_FAULT: if (faulthandler_disabled() || !mm) goto out; break; }
would no longer work since faulthandler_disabled checks for the preempt count.
| |