RE: [Xen-ia64-devel] lsapic deliver external IRQ

["Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>]

While Xen/ia64 is executing, interrupts are generally enabled
(and, indeed, may even nest).  If, while Xen is executing,
an interrupt arrives that results in a pending interrupt
for the currently active guest domain, the interrupt needs
to be immediately delivered/injected.  That's why vcpu_pend_interrupt
is called when Xen is about to return to the active domain.
Without this check it might be a very long time before the
guest gets the interrupt. 

> -----Original Message-----
> From: xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf 
> Of Dong, Eddie
> Sent: Saturday, April 30, 2005 1:59 AM
> To: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-ia64-devel] lsapic deliver external IRQ
> 
> Dan:
>       I guess you will get all our code today or tomorrow, so we may
> go to much details.
>       In ia64_leave_kernel assembly code, the current implementation
> is invoking deliver_pending_interrupt to check if there is any pending
> IRQ that can be injected and inject if it can. What in my mind is like
> followings:
>       Within vcpu_pend_interrupt (when guest IRQ signal is fired), VMM
> do deliver_pending_interrupt() to determine if there is any chance to
> inject guest EX-IRQ. But It is possible that guest ex-IRQ is unable to
> inject at that time and thus pending in vIRR due to vpsr.i or vtpr.
> Within psr/tpr privillege resource update fault, if the guest enables
> vpsr.i or updates TPR, VMM will call 
> deliver_pending_interrupt again to
> re-determine if VMM needs to inject guest ex-IRQ. This is much like an
> event driving guest EX-IRQ injecting mechanism while current 
> one is much
> like a polling mechanism.
>       How about this? If you agree, I will provide a patch for this.
> Eddie
> 
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