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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 15 Mar 2023, 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.
> 
> 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.

I'll let Ray reply here, but I think you are right:
HYSDEVOP_{un,}map_pirq are needed so that QEMU can run in PVH Dom0 to
support HVM guests.