Il 26/02/2014 21:27, Stefan Bader ha scritto: > 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 I don't have my usual test machine available, but here is a possible guess. nested_read_cr0 is the CR0 as read by L2, but here we want to look at the CR0 value reflecting L1's setup. This would suggest the following untested patch: diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index a06f101ef64b..0d90601a2681 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6688,7 +6688,7 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu) else if (is_page_fault(intr_info)) return enable_ept; else if (is_no_device(intr_info) && - !(nested_read_cr0(vmcs12) & X86_CR0_TS)) + !(vmcs12->guest_cr0 & X86_CR0_TS)) return 0; return vmcs12->exception_bitmap & (1u << (intr_info & INTR_INFO_VECTOR_MASK)); Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
