Bug 202419

Summary: KVM 4.14.94 regression due to "x86,kvm: move qemu/guest FPU switching out to vcpu_run"
Product: Virtualization Reporter: Roman Mamedov (rm+bko)
Component: kvmAssignee: virtualization_kvm
Status: RESOLVED CODE_FIX    
Severity: normal CC: borntraeger, riel, rkrcmar, seanjc
Priority: P1    
Hardware: x86-64   
OS: Linux   
Kernel Version: 4.14.94 Subsystem:
Regression: Yes Bisected commit-id:
Attachments: dmesg of the crash

Description Roman Mamedov 2019-01-25 17:52:08 UTC 
Created attachment 280773 [details]
dmesg of the crash

Hello,

I have a VM which works fine on 4.14.93, but started crashing on boot in a very puzzling way on 4.14.94 (dmesg attached) and 4.14.95.

Given the latter two have pretty much one KVM-on-x86 related change [1] since 4.14.93, sure enough, rolling back that one makes it work again (on 4.14.95).

It is really weird, how would an FPU change affect loading libraries? But I double-checked that there's no mistake and no changes are happening within the guest initrd, libraries and such. Only switching the kernel on the host between with/without that patch, determines whether the VM will boot or not.

Any idea what might be going on here?

Thanks

[1] https://patchwork.kernel.org/patch/10058409/