Re: [PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v2)

[Avi Kivity <avi@redhat.com>]

On 12/04/2010 03:48 PM, Anthony Liguori wrote:
>> No, an interrupt causes the HLT to be executed, and rip advanced past 
>> it.  You need to preserve this (both for interrupts and for the apf 
>> completion exception).
>
>
> Yeah, I see in the architecture manual it specifically calls out the 
> rip advancing after NMI.  It doesn't say anything about debug 
> exceptions though. 

Instruction breakpoints are triggered before HLT executes; and HLT can't 
trigger data breakpoints.

> It's not clear to me if some exceptions cause hlt to be skipped and 
> others not.

Faults take place before HLT is executed (and thus don't advance RIP).  
Interrupts take place during HLT execution and cause it to complete.

>
> But then again, skipping hlt seems to be the most conservative thing 
> to do for all exceptions because it's always going to be run in a loop.

There's no "all exceptions" here.  Only interrupts can happen, and the 
APF completion, which is wired to a fault vector, but we must treat it 
as an interrupt.

-- 
error compiling committee.c: too many arguments to function