Re: [Qemu-devel] [RFC] create a single workqueue for each vm to update vm irq routing table

[Paolo Bonzini]

Il 28/11/2013 10:19, Gleb Natapov ha scritto:
> Not changing current behaviour is certainly safer, but I am still not 100%
> convinced we have to ensure this.
> 
> Suppose guest does:
> 
> 1: change msi interrupt by writing to pci register
> 2: read the pci register to flush the write
> 3: zero idt
> 
> I am pretty certain that this code can get interrupt after step 2 on real HW,
> but I cannot tell if guest can rely on it to be delivered exactly after
> read instruction or it can be delayed by couple of instructions.

I agree it's fragile, but if a dedicated SRCU can meet the requirements
(possibly with synchronize_srcu_expedited), I prefer not to break it.

Paolo

 Seems to me
> it would be fragile for an OS to depend on this behaviour. AFAIK Linux does 
> not.