Re: nVMX regression v3.13+, bisected

[Paolo Bonzini <pbonzini@redhat.com>]

Il 26/02/2014 20:43, Stefan Bader ha scritto:
> Hi,
>
> I was looking at a bug report[1] about a regression on nested VMX that started
> with kernel v3.13 (same issue still existed with v3.14-rc4). The problem shows
> up when running a v3.13 kernel in L0 and then trying to launch a L2 (L1 was
> either a v3.2 kernel or v3.13, so seemed to have no immediate influence). L2 is
> trying to boot a iso image and hangs before the isolinux boot loader displays
> anything. A preinstalled hd image fails to boot, too.
>
> I bisected this and ended up on the following commit which, when reverted made
> the launch work again:
>
> Author: Anthoine Bourgeois <bourgeois@bertin.fr>
> Date:   Wed Nov 13 11:45:37 2013 +0100
>
>     kvm, vmx: Fix lazy FPU on nested guest
>
>     If a nested guest does a NM fault but its CR0 doesn't contain the TS
>     flag (because it was already cleared by the guest with L1 aid) then we
>     have to activate FPU ourselves in L0 and then continue to L2. If TS flag
>     is set then we fallback on the previous behavior, forward the fault to
>     L1 if it asked for.
>
>     Signed-off-by: Anthoine Bourgeois <bourgeois@bertin.fr>
>     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>
> The condition to exit to L0 seems to be according to what the description says.
> Could it be that the handling in L0 is doing something wrong?

Thanks, I'll look at it tomorrow or Friday.

Paolo