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From:   Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Subject: Re: [PATCH] kvm: ioapic: Introduce arch-specific check for lazy
 update EOI mechanism
To:     Paolo Bonzini <pbonzini@redhat.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     rkrcmar@redhat.com, joro@8bytes.org, jon.grimm@amd.com,
        borisvk@bstnet.org
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Paolo,

On 4/25/20 4:52 PM, Paolo Bonzini wrote:
> On 24/04/20 07:08, Suravee Suthikulpanit wrote:
>> commit f458d039db7e ("kvm: ioapic: Lazy update IOAPIC EOI") introduces
>> the following regression on Intel VMX APICv.
>>
>> BUG: stack guard page was hit at 000000008f595917 \
>> (stack is 00000000bdefe5a4..00000000ae2b06f5)
>> kernel stack overflow (double-fault): 0000 [#1] SMP NOPTI
>> RIP: 0010:kvm_set_irq+0x51/0x160 [kvm]
>> Call Trace:
>>   irqfd_resampler_ack+0x32/0x90 [kvm]
>>   kvm_notify_acked_irq+0x62/0xd0 [kvm]
>>   kvm_ioapic_update_eoi_one.isra.0+0x30/0x120 [kvm]
>>   ioapic_set_irq+0x20e/0x240 [kvm]
>>   kvm_ioapic_set_irq+0x5c/0x80 [kvm]
>>   kvm_set_irq+0xbb/0x160 [kvm]
>>   ? kvm_hv_set_sint+0x20/0x20 [kvm]
>>   irqfd_resampler_ack+0x32/0x90 [kvm]
>>   kvm_notify_acked_irq+0x62/0xd0 [kvm]
>>   kvm_ioapic_update_eoi_one.isra.0+0x30/0x120 [kvm]
>>   ioapic_set_irq+0x20e/0x240 [kvm]
>>   kvm_ioapic_set_irq+0x5c/0x80 [kvm]
>>   kvm_set_irq+0xbb/0x160 [kvm]
>>   ? kvm_hv_set_sint+0x20/0x20 [kvm]
>> ....
>>
>> This is due to the logic always force IOAPIC lazy update EOI mechanism
>> when APICv is activated, which is only needed by AMD SVM AVIC.
>>
>> Fixes by introducing struct kvm_arch.use_lazy_eoi variable to specify
>> whether the architecture needs lazy update EOI support.
> 
> You are not explaining why the same infinite loop cannot happen on AMD.
>   It seems to me that it is also fixed by adding a check for re-entrancy
> in ioapic_lazy_update_eoi.  It's easy to add one since
> ioapic_lazy_update_eoi is called with the ioapic->lock taken.
> 
> Paolo
> 

I finally reproduced on AMD system as well. I'll send out a new patch for this based on your suggestion.

Suravee