Re: [Xen-devel] [Xenhackthon] Virtualized APIC registers - virtual interrupt delivery.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, May 23, 2013 at 08:25:06AM +0000, Zhang, Yang Z wrote:
> Jan Beulich wrote on 2013-05-23:
> >>>> On 22.05.13 at 18:21, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > wrote:
> >> Which means that if this is set to be higher than the hypervisor timer
> >> or IPI callback the guest can run unbounded. Also it would seem that
> >> this value has to be often reset when migrating a guest between the pCPUs.
> >> And it would appear that this value is static. Meaning the guest only
> >> sets these vectors once and the hypervisor is responsible for managing
> >> the priority of that guest and other guests (say dom0) on the CPU.
> >> 
> >> For example, we have a guest with a 10gB NIC and the guest has decided
> >> to use vector 0x80 for it (assume a UP guest). Dom0 has an SAS controller
> >> and is using event number 30, 31, 32, and 33 (there are only 4 PCPUS).
> >> The hypervisor maps them to be 0x58, 0x68, 0x78 and 0x88 and spreads those
> >> vectors on each pCPU. The guest is running on pCPU1 and there are two
> >> vectors - 0x80 and 0x58. The one assigned to the guest wins and dom0
> >> SAS controller is preempted.
> >> 
> >> The solution for that seems to have some interaction with the
> >> guest when it allocates the vectors so that they are always below
> >> the dom0 priority vectors. Or hypervisor has to dynamically shuffle its
> >> own vectors to be higher priority.
> >> 
> >> Or is there an guest vector <-> hypervisor vector lookup table that
> >> the CPU can use? So the hypervisor can say: the vector 0x80 in the
> >> guest actually maps to vector 0x48 in the hypervisor?
> > 
> > It is my understanding that the vector spaces are separate, and
> > hence guest interrupts can't block host ones (like the timer). Iirc
> Right. virtual interrupt delivery only for delivering guest virtual 
> interrupt(from emulation device and assigned device.) which is located in 
> guest's vector space. It has nothing to do with other guest.


OK, in which case Linux ~v2.6.32 (when the event callback mechanism was
introduced for HVM guests) will _not_ take advantage of this, right?

Is there a way to solve this so that they _will_ take advantage of this.
> 
> > there's some sort of flag bit in the IRTE to tell whether an interrupt
> > should get delivered directly to the guest, or to the hypervisor.
> I think you are talking about Posted interrupt.
> 
> > 
> > Jan
> > 
> > Jan
> 
> 
> Best regards,
> Yang
> 
> 
> 
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