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Re: [Xen-devel] anomaly in irq check in fixup_page_fault()

To: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
Subject: Re: [Xen-devel] anomaly in irq check in fixup_page_fault()
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Fri, 22 Jul 2011 07:22:16 +0100
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Thread-topic: [Xen-devel] anomaly in irq check in fixup_page_fault()
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On 21/07/2011 20:28, "Mukesh Rathor" <mukesh.rathor@xxxxxxxxxx> wrote:

> On Thu, 21 Jul 2011 07:35:00 +0100
> Keir Fraser <keir.xen@xxxxxxxxx> wrote:
>> On 21/07/2011 02:30, "Mukesh Rathor" <mukesh.rathor@xxxxxxxxxx> wrote:
>> A PV guest never has EF.IF=0, so the early exit should never be
>> triggered by a guest fault.
>> Your best bet is to fake this out in your HVM container wrapper. Just
>> write an EFLAGS into the saved regs that has EF.IF=1, as would always
>> be the case for a normal PV guest. Rather that than fragile
>> eis_hvm_pv() checks scattered around.
> Ok. In my prototype, i've the check, but I'll do the wrapper. I realize
> now the above check is more for hyp not taking fault disabled than the
> guest doing so.
>> The setting of EF.IF shouldn't matter much for your guest as you'll
>> be doing PV event delivery anyway, but I wonder how it ends up with
>> EF.IF=0 -- is that deliberate?
> Yeah, I change IF=0 initially to make sure events are not delivered
> until the guest is ready and does irq enable. For PV, the vcpu-mask=1
> assures this. Unlike PV, the hybrid changes IF in
> enable/disable to make "interrupt window exiting" work, BTW.

I hope this can be an optional extension in the final version.

 -- Keir

> thanks,
> Mukesh

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