[Bug 206579] KVM with passthrough generates "BUG: kernel NULL pointer dereference" and crashes

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=206579

--- Comment #37 from Anthony (anthonysanwo@googlemail.com) ---
Created attachment 287701
  --> https://bugzilla.kernel.org/attachment.cgi?id=287701&action=edit
Perf_stat_anthony_apicv

(In reply to Suravee Suthikulpanit from comment #32)
> (In reply to Anthony from comment #28)
> > Created attachment 287685 [details]
> > avic_inhibit_reasons-anthony
> > 
> > Hi I also just wanted to give my observations I have found when testing the
> > patches.
> > 
> > I confirm I also don't have don't have crashes relating to the original
> > report. 
> > 
> > I have been trying out the SVM AVIC patches since around the first patch
> > that was submitted but never got round to documentation my testing until
> > recently.
> > 
> > I can't remember the specific patch set/kernel version I tried but I
> > remember having avic apparently working with when synic + stimer where
> > enabled but not without. If my understanding is correctly this shouldn't be
> > the case as synic is meant to be a case when avic is permanently disabled.
> > 
> > This is still the case with current patchset. 
> > 
> > In summary I can get avic reporting it's working according to perf stat and
> > trace logs when synic is on but not working when synic is off. Using
> > EPYC-IBPB or passthrough doesn't change the avic_inhibit_reasons.
> > 
> > With Synic I get avic_inhibit_reasons - 10
> > With Synic+Stimer off I get - 0
> > 
> > 
> > To note I am using arch linux + qemu 4.2 + linux-mainline-5.6.0-rc2.
> > 
> > Please see a small trace log of synic on vs off, domain capabilities, perf
> > stat and patches used.
> > 
> > These were recording once the VM was launched and sitting at the login
> > screen.
> > 
> > Please let me know if there is any other info I get provide to help.
> 
> Thanks for the observation info, and your observation makes sense. AVIC is
> also deactivated w/ synic enabled.
> (https://elixir.bootlin.com/linux/v5.6-rc3/source/arch/x86/kvm/hyperv.c#L773)
> 
> Thanks,
> Suravee

I see. I remember reading through your patchset and trying work things out good
to see my basic understanding wasn't too far off :)

If it's not too much of a bother I was wondering if you could list the
requirements needed to enable avic from a kvm/qemu setup. I just wanted to
check if I am missing anything on my side as I am not 100% sure on how to tell
avic is working looking a trace, perf stat/live. 

I did a perf stat from when the vm was launch via libvirt to about when it gets
to the login screen I about 36 "kvm_apicv_update_request".The attachement has a
full output if that is of use. I also got a trace of this but as I redirected
all the output to a file I ended up with quite a large file(462MB). So I wanted
to see if there is anything I should be looking out for in the trace to see if
avic is working as intended. Also, if you don't mind could you show a sample of
trace where avic is working.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.