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SubjectRe: [PATCH v3] KVM: nVMX: Fix incorrect preemption timer vmexit in nested guest

On 06/07/2016 18:03, Haozhong Zhang wrote:
>>> This patch also fixed the crash of L1 Xen with L2 HVM guest. Xen does
>>> not enable preemption timer for HVM guests, and will get panic if it
>>> receives a preemption timer vmexit.
>> Thanks! I'm still not sure why the bit is set in the vmcs02 though...
> Yes, it looks really weird.
> I replaced "return false" in Wanpeng's patch by
> pr_info("VMCS: preemption timer enabled = %d\n",
> and redid my test. As expected, L1 Xen crashed due to the unexpected
> preemption timer vmexit. I got a log from above statement just before crash:
> VMCS: preemption timer enabled = 1
> which is expected to be 0, because preemption timer is disabled in
> vmcs02. I also modified L1 Xen to dump VMCS at crash, and it says
> preemption timer is disabled.
> I noticed Jim Mattson recently sent a patch "KVM: nVMX: Fix memory
> corruption when using VMCS shadowing" to fix the inconsistency between
> vmcs12 and its shadow. Is it relevant here? I'll test his patch
> tomorrow.

No, it shouldn't have any effect.

I think it happens when the post_block hook switches back from sw_timer
to hv_timer, and L2 is running. So the right fix should be along the
lines of what I posted earlier. If you don't beat me to it, I'll take
another look tomorrow.


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