On 26.02.2014 21:25, Paolo Bonzini wrote: > 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@xxxxxxxxx> >> 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@xxxxxxxxx> >> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> >> >> 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 > Great thanks. And maybe it helps if I actually add the link to the bug report as I had intended... :-P [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1278531
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