On Fri, May 20, 2022, Brian Cowan wrote:
> Disabling smap seems to fix the problem...
Mwhahaha, I should have found someone to bet me real money :-)
> Now for the hard question: WHY?
The most likely scenario it that there's a SMAP violation (#PF due to a kernel
access to user data without an override to tell the CPU that the access is intentional)
somewhere in the guest that crashes/panics the guest kernel. Assuming that's the
case, there are three-ish possibilities:
1. There's a bug your company's custom kernel driver.
2. There's a SMAP violation somewhere else in RHEL 7.8, which is an 8+ year old
frankenkernel...
3. There's a bug in your version of KVM related to SMAP virtualization
#3 begs the question, does this fail on bare metal that supports SMAP? If so,
then that rules out #3.
If the crash occurs only when doing stuff related to your custom driver, #1 is
most likely the culprit.
One way to try and debug further would be to disable EPT in KVM (load kvm_intel with
ept=0) and then use KVM tracepoints to see when the guest dies. If it's a SMAP
violation, there should be an injected SMAP #PF shortly before the guest dies.
