Re: [PATCH 2/3] KVM: x86: guest debug: don't inject interrupts while single stepping

Sean Christopherson
2021-03-16T17:28:10Z

On Tue, Mar 16, 2021, Jan Kiszka wrote:
> On 16.03.21 17:50, Sean Christopherson wrote:
> > Rather than block all events in KVM, what about having QEMU "pause" the timer?
> > E.g. save MSR_TSC_DEADLINE and APIC_TMICT (or inspect the guest to find out
> > which flavor it's using), clear them to zero, then restore both when
> > single-stepping is disabled. I think that will work?
> >
>
> No one can stop the clock, and timers are only one source of interrupts.
> Plus they do not all come from QEMU, some also from KVM or in-kernel
> sources directly.

But are any other sources of interrupts a chronic problem? I 100% agree that
this would not be a robust solution, but neither is blocking events in KVM. At
least with this approach, the blast radius is somewhat contained.

> Would quickly become a mess.

Maybe, but it'd be Qemu's mess ;-)