Re: [RFC XEN PATCH 3/6] x86/pvh: shouldn't check pirq flag when map pirq in PVH

[Huang Rui <ray.huang@xxxxxxx>]

On Wed, Mar 15, 2023 at 11:57:45PM +0800, Roger Pau Monné wrote:
> On Sun, Mar 12, 2023 at 03:54:52PM +0800, Huang Rui wrote:
> > From: Chen Jiqian <Jiqian.Chen@xxxxxxx>
> > 
> > PVH is also hvm type domain, but PVH hasn't X86_EMU_USE_PIRQ
> > flag. So, when dom0 is PVH and call PHYSDEVOP_map_pirq, it
> > will fail at check has_pirq();
> > 
> > Signed-off-by: Chen Jiqian <Jiqian.Chen@xxxxxxx>
> > Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
> > ---
> >  xen/arch/x86/hvm/hypercall.c | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/xen/arch/x86/hvm/hypercall.c b/xen/arch/x86/hvm/hypercall.c
> > index 405d0a95af..16a2f5c0b3 100644
> > --- a/xen/arch/x86/hvm/hypercall.c
> > +++ b/xen/arch/x86/hvm/hypercall.c
> > @@ -89,8 +89,6 @@ long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
> > arg)
> >      case PHYSDEVOP_eoi:
> >      case PHYSDEVOP_irq_status_query:
> >      case PHYSDEVOP_get_free_pirq:
> > -        if ( !has_pirq(currd) )
> > -            return -ENOSYS;
> 
> Since I've taken a look at the Linux side of this, it seems like you
> need PHYSDEVOP_map_pirq and PHYSDEVOP_setup_gsi, but the later is not
> in this list because has never been available to HVM type guests.

Do you mean HVM guest only support MSI(-X)?

> 
> I would like to better understand the usage by PVH dom0 for GSI
> passthrough before deciding on what to do here.  IIRC QEMU also uses
> PHYSDEVOP_{un,}map_pirq in order to allocate MSI(-X) interrupts.
> 

The MSI(-X) interrupt doesn't work even on the passthrough device at domU
even the dom0 is PV domain. It seems a common problem, I remember Christian
encountered the similar issue as well. So we fallback to use the GSI
interrupt instead.

Thanks,
Ray