Re: [RFC XEN PATCH v3 2/3] x86/pvh: Add (un)map_pirq and setup_gsi for PVH dom0

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

On Mon, Dec 11, 2023 at 12:40:08AM +0800, Jiqian Chen wrote:
> If run Xen with PVH dom0 and hvm domU, hvm will map a pirq for
> a passthrough device by using gsi, see
> xen_pt_realize->xc_physdev_map_pirq and
> pci_add_dm_done->xc_physdev_map_pirq. Then xc_physdev_map_pirq
> will call into Xen, but in hvm_physdev_op, PHYSDEVOP_map_pirq
> is not allowed because currd is PVH dom0 and PVH has no
> X86_EMU_USE_PIRQ flag, it will fail at has_pirq check.
> So, allow PHYSDEVOP_map_pirq when currd is dom0 no matter if
> dom0 has X86_EMU_USE_PIRQ flag and also allow
> PHYSDEVOP_unmap_pirq for the failed path to unmap pirq.
> 
> What's more, in PVH dom0, the gsis don't get registered, but
> the gsi of a passthrough device must be configured for it to
> be able to be mapped into a hvm domU.
> So, add PHYSDEVOP_setup_gsi for PVH dom0, because PVH dom0
> will setup gsi during assigning a device to passthrough.
> 
> Co-developed-by: Huang Rui <ray.huang@amd.com>
> Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
> ---
>  xen/arch/x86/hvm/hypercall.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/hypercall.c b/xen/arch/x86/hvm/hypercall.c
> index 6ad5b4d5f1..621d789bd3 100644
> --- a/xen/arch/x86/hvm/hypercall.c
> +++ b/xen/arch/x86/hvm/hypercall.c
> @@ -72,8 +72,11 @@ long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
>  
>      switch ( cmd )
>      {
> +    case PHYSDEVOP_setup_gsi:

I think given the new approach on the Linux side patches, where
pciback will configure the interrupt, there's no need to expose
setup_gsi anymore?

>      case PHYSDEVOP_map_pirq:
>      case PHYSDEVOP_unmap_pirq:
> +        if ( is_hardware_domain(currd) )
> +            break;

Also Jan already pointed this out in v2: this hypercall needs to be
limited so a PVH dom0 cannot execute it against itself.  IOW: refuse
the hypercall if DOMID_SELF or the passed domid matches the current
domain domid.

Thanks, Roger.