Re: [Xen-devel] [RFC PATCH] hvm/vpt: fix inconsistent views of vIOAPIC in vmx_intr_assist()

[Chao Gao <chao.gao@xxxxxxxxx>]

On Wed, Apr 12, 2017 at 02:45:36AM +0000, Xuquan (Quan Xu) wrote:
>On April 07, 2017 11:24 AM, Chao Gao wrote:
>>When injecting periodic timer interrupt in vmx_intr_assist(), multiple read
>>operation is operated during one event delivery and incur to inconsistent
>>views of vIOAPIC. For example, if a periodic timer interrupt is from PIT, when
>>set the corresponding bit in vIRR, the corresponding RTE is accessed in
>>pt_update_irq(). When this function returns, it accesses the RTE again to get
>>the vector it set in vIRR.  Between the two accesses, the content of RTE may
>>have been changed by another CPU for no protection method in use. This case
>>can incur the assertion failure in vmx_intr_assist().  Also after a periodic
>>timer interrupt is injected successfully, pt_irq_posted() will decrease the
>>count (pending_intr_nr). But if the corresponding RTE has been changed,
>>pt_irq_posted() will not decrease the count, resulting one more timer
>>interrupt.
>>
>>More discussion and history can be found in
>>1.https://lists.xenproject.org/archives/html/xen-devel/2017-03/msg00906.ht
>>ml
>>2.https://lists.xenproject.org/archives/html/xen-devel/2017-01/msg01019.ht
>>ml
>>
>>+    /*
>>+     * Avoid the vIOAPIC RTE being changed by another vCPU.
>
>This comment seems inconsistent with the patch description, which said ' by 
>another CPU ', instead of 'by another vCPU'..
>

[Sorry. I ignored this in the previous email.]
Yes. Should be 'by another vCPU'.

Thanks
Chao

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