Virtual Interrupt Delivery

Virtual Interrupt Delivery

[Dmitry Rockosov]

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Hi guys,

Do you know when *recognized* Virtual Interrupt on VM-Entry will be
delivered if Virtual-Interrupt Delivery is enabled and interrupt delivery
is blocking by STI?

Previously, VMM used Interrupt-Window, but as I see in XEN code,
Interrupt-Window
is not used when Virtual Interrupt Delivery is enabled.

Does it mean, we will get Virtual Interrupt on the next VM-entry?

Thank you!

Best Regards,
Rockosov Dmitry

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Re: Virtual Interrupt Delivery

[Konrad Rzeszutek Wilk]

On Mon, Feb 27, 2017 at 09:13:29PM +0300, Dmitry Rockosov wrote:
> Hi guys,
> 
> Do you know when *recognized* Virtual Interrupt on VM-Entry will be
> delivered if Virtual-Interrupt Delivery is enabled and interrupt delivery
> is blocking by STI?

This sounds like a good question to the Intel maintainers, CC-ing them.

> 
> Previously, VMM used Interrupt-Window, but as I see in XEN code,
> Interrupt-Window
> is not used when Virtual Interrupt Delivery is enabled.

Right, the Intel SDM has a whole section about that.
> 
> Does it mean, we will get Virtual Interrupt on the next VM-entry?

By my understanding of the Intel SDM it depends on whether the
vector is one of those that the CPU can inject without involving
the VMM.

I would recommend you read the Intel SDM - the answer may be right
there.

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Re: Virtual Interrupt Delivery

[Tian, Kevin]

> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com]
> Sent: Thursday, March 02, 2017 4:36 AM
> 
> On Mon, Feb 27, 2017 at 09:13:29PM +0300, Dmitry Rockosov wrote:
> > Hi guys,
> >
> > Do you know when *recognized* Virtual Interrupt on VM-Entry will be
> > delivered if Virtual-Interrupt Delivery is enabled and interrupt delivery
> > is blocking by STI?
> 
> This sounds like a good question to the Intel maintainers, CC-ing them.

virtual interrupt delivery doesn't change the implication of blocking
by STI. It will be evaluated and delivered when it's allowed.

> 
> >
> > Previously, VMM used Interrupt-Window, but as I see in XEN code,
> > Interrupt-Window
> > is not used when Virtual Interrupt Delivery is enabled.
> 
> Right, the Intel SDM has a whole section about that.
> >
> > Does it mean, we will get Virtual Interrupt on the next VM-entry?
> 
> By my understanding of the Intel SDM it depends on whether the
> vector is one of those that the CPU can inject without involving
> the VMM.
> 
> I would recommend you read the Intel SDM - the answer may be right
> there.

yes SDM has a very clear description of when a virtual interrupt 
delivery will happen. check CH29.2 (Evaluation and Delivery of
Virtual Interrupts).

Thanks
Kevin

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