From: Paolo Bonzini <pbonzini@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>, kvm@vger.kernel.org
Cc: "Radim Krčmář" <rkrcmar@redhat.com>,
"Liran Alon" <liran.alon@oracle.com>,
"Sean Christopherson" <sean.j.christopherson@intel.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC] KVM: x86: vmx: throttle immediate exit through preemtion timer to assist buggy guests
Date: Fri, 29 Mar 2019 16:01:13 +0100 [thread overview]
Message-ID: <89d4189b-de6a-7634-de8b-29a044a86e12@redhat.com> (raw)
In-Reply-To: <87d0m93frp.fsf@vitty.brq.redhat.com>
On 29/03/19 15:40, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
>
>> On 28/03/19 21:31, Vitaly Kuznetsov wrote:
>>>
>>> The 'hang' scenario develops like this:
>>> 1) Hyper-V boots and QEMU is trying to inject two irq simultaneously. One
>>> of them is level-triggered. KVM injects the edge-triggered one and
>>> requests immediate exit to inject the level-triggered:
>>>
>>> kvm_set_irq: gsi 23 level 1 source 0
>>> kvm_msi_set_irq: dst 0 vec 80 (Fixed|physical|level)
>>> kvm_apic_accept_irq: apicid 0 vec 80 (Fixed|edge)
>>> kvm_msi_set_irq: dst 0 vec 96 (Fixed|physical|edge)
>>> kvm_apic_accept_irq: apicid 0 vec 96 (Fixed|edge)
>>> kvm_nested_vmexit_inject: reason EXTERNAL_INTERRUPT info1 0 info2 0 int_info 80000060 int_info_err 0
>>>
>>> 2) Hyper-V requires one of its VMs to run to handle the situation but
>>> immediate exit happens:
>>>
>>> kvm_entry: vcpu 0
>>> kvm_exit: reason VMRESUME rip 0xfffff80006a40115 info 0 0
>>> kvm_entry: vcpu 0
>>> kvm_exit: reason PREEMPTION_TIMER rip 0xfffff8022f3d8350 info 0 0
>>> kvm_nested_vmexit: rip fffff8022f3d8350 reason PREEMPTION_TIMER info1 0 info2 0 int_info 0 int_info_err 0
>>> kvm_nested_vmexit_inject: reason EXTERNAL_INTERRUPT info1 0 info2 0 int_info 80000050 int_info_err 0
>>
>> I supposed before this there was an eoi for vector 96?
>
> AFAIR: no, it seems that it is actually the VM it is trying to resume
> (Windows partition?) which needs to do some work and with the preemtion
> timer of 0 we don't allow it to.
kvm_apic_accept_irq placed IRQ 96 in IRR, and Hyper-V should be running
with "acknowledge interrupt on exit" since int_info is nonzero in
kvm_nested_vmexit_inject.
Therefore, at the kvm_nested_vmexit_inject tracepoint KVM should have
set bit 96 in ISR; and because PPR is now 96, interrupt 80 should have
never been delivered. Unless 96 is an auto-EOI interrupt, in which case
this comment would apply
/*
* For auto-EOI interrupts, there might be another pending
* interrupt above PPR, so check whether to raise another
* KVM_REQ_EVENT.
*/
IIRC there was an enlightenment to tell Windows "I support auto-EOI but
please don't use it". If this is what's happening, that would also fix it.
Thanks,
Paolo
next prev parent reply other threads:[~2019-03-29 15:01 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-28 20:31 [PATCH RFC] KVM: x86: vmx: throttle immediate exit through preemtion timer to assist buggy guests Vitaly Kuznetsov
2019-03-29 2:00 ` Liran Alon
2019-03-29 9:14 ` Vitaly Kuznetsov
2019-03-29 12:09 ` Liran Alon
2019-03-29 14:18 ` Paolo Bonzini
2019-03-29 14:40 ` Vitaly Kuznetsov
2019-03-29 15:01 ` Paolo Bonzini [this message]
2019-03-29 15:14 ` Vitaly Kuznetsov
2019-03-29 15:32 ` Liran Alon
2019-03-29 17:14 ` Paolo Bonzini
2019-04-01 8:39 ` Vitaly Kuznetsov
2019-04-01 10:08 ` Liran Alon
2019-04-01 10:41 ` Vitaly Kuznetsov
2019-04-01 8:50 ` Vitaly Kuznetsov
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