[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 #32 from Suravee Suthikulpanit (suravee.suthikulpanit@amd.com) ---
(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

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