Re: [Xen-devel] [PATCH v3] VT-d PI: disable VT-d PI when APICv is disabled

[Chao Gao <chao.gao@xxxxxxxxx>]

On Fri, Jun 09, 2017 at 02:43:30AM -0600, Jan Beulich wrote:
>>>> On 09.06.17 at 08:22, <chao.gao@xxxxxxxxx> wrote:
>> --- a/xen/arch/x86/hvm/vmx/vmcs.c
>> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
>> @@ -351,6 +351,13 @@ static int vmx_init_vmcs_config(void)
>>            || !(_vmx_vmexit_control & VM_EXIT_ACK_INTR_ON_EXIT) )
>>          _vmx_pin_based_exec_control  &= ~ PIN_BASED_POSTED_INTERRUPT;
>>  
>> +    if ( iommu_intpost && !cpu_has_vmx_posted_intr_processing )
>> +    {
>> +        printk("Intel VT-d Posted Interrupt is disabled for CPU-side Posted 
>> "
>> +               "Interrupt is not enabled\n");
>> +        iommu_intpost = 0;
>> +    }
>
>So simply clearing iommu_intpost here indeed looks to be fine (at
>least for all current uses of the flag). However, previously you
>had a dependency on APIC-V being enabled, and there not longer
>is such a dependency with the check above -
>posted_intr_processing is being forced to off only when
>!vmx_virtual_intr_delivery or ACK_INTR_ON_EXIT not being set
>(the latter btw is strange as a check, as that feature is being
>requested as "minimum", not "optional").

Yes. the relevant description is improper now. I will remove all of
them and think more about the ACK_INTR_ON_EXIT. If it can be
removed, I will take this change to do this.

>
>And then I have a flow question here:
>cpu_has_vmx_posted_intr_processing expands to a reference to
>vmx_pin_based_exec_control, yet that variable is being written
>only later in the function, so it would seem to me that now you
>turn off iommu_intpost unconditionally. Am I overlooking anything?
>Otherwise I think you need to use _vmx_pin_based_exec_control
>here instead, just like the code visible in context does.

Agree. It should be. Thanks you. I forgot to test with 'apicv=true'.
I only tested this patch with 'apicv=false'.

Thanks
chao

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