Re: pv_ops smp support

[Jeremy Fitzhardinge <jeremy@goop.org>]

Zachary Amsden wrote:
> No, I don't mean the Linux PDA - how do you access the Xen PDA?  Or 
> have they conjoined somehow?

You could put it that way I guess.  There's a generic Linux PDA; a 
paravirt patch adds a union for pv use, and a Xen patch adds a 
Xen-specific element to that union.  That's how it has been from the 
start, so there wasn't really anything to conjoin (there was never a Xen 
PDA per se).

> So your invalidate "IPI" is actually a hypercall, and you can use the 
> existing flush_tlb interface for the most part.  You just need a 
> paravirt-op then for the IPI itself, which takes a CPU mask - and this 
> seems to match nicely onto your hypercall.
Yep.  There are calls for flushing the whole tlb, and for just a page; 
both take CPU masks.

> I think you might want to optimize this a bit more, however, since in 
> some cases you will issue implicit shootdown IPIs during a pte update 
> hypercall.

Not that I've seen, at least none that doesn't also exist in baseline.

> This seems much cleaner than designing the shootdown semantic directly 
> into such PTE updates, which is I believe what some of the older Xen 
> patches did, although I could have misread them.

I was starting on SMP with the idea that it would be relatively isolated 
and simple, but it seems I should probably do the MMU stuff first to see 
what impact it has on SMP.

    J