Re: [PATCH v3.1 01/15] xen/x86: remove XENFEAT_hvm_pirqs for PVHv2 guests

[Roger Pau Monne <roger.pau@citrix.com>]

On Thu, Nov 03, 2016 at 06:52:16AM -0600, Jan Beulich wrote:
> >>> On 03.11.16 at 13:35, <roger.pau@citrix.com> wrote:
> > --- a/docs/misc/hvmlite.markdown
> > +++ b/docs/misc/hvmlite.markdown
> > @@ -75,3 +75,38 @@ info structure that's passed at boot time (field rsdp_paddr).
> >  
> >  Description of paravirtualized devices will come from XenStore, just as it's
> >  done for HVM guests.
> > +
> > +## Interrupts ##
> > +
> > +### Interrupts from physical devices ###
> > +
> > +Interrupts from physical devices are delivered using native methods, this is
> > +done in order to take advantage of new hardware assisted virtualization
> > +functions, like posted interrupts.
> 
> Okay, that's a reason for this to be optional (iirc AMD doesn't
> have posted interrupts so far), not for all the physdev ops being
> made not work at all. The more that I think I did point out before
> that there is at least one case where interrupt delivery info
> needs to be made available to Xen despite Dom0 not setting up
> an IO-APIC entry, and hence a physdev op is the only way to
> communicate that information.

IIRC we already had this discussion earlier, and the only thing that could 
need such information is a serial console that uses a non ISA IRQ, which we 
can also drive in polling mode. IMHO we can always enable some PHYSDEV ops 
if they are strictly necessary, but I would like to start with as few (ie: 
none) as possible.

Roger.

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