[XEN PATCH v15 1/4] x86/hvm: allow {,un}map_pirq hypercalls unconditionally

[Jiqian Chen <Jiqian.Chen@xxxxxxx>]

The current hypercall interfaces to manage and assign interrupts to
domains is mostly based in using pIRQs as handlers.  Such pIRQ values
are abstract domain-specific references to interrupts.

Classic HVM domains can have access to {,un}map_pirq hypercalls if the
domain is allowed to route physical interrupts over event channels.
That's however a different interface, limited to only mapping
interrupts to itself. PVH domains on the other hand never had access
to the interface, as PVH domains are not allowed to route interrupts
over event channels.

In order to allow setting up PCI passthrough from a PVH domain it
needs access to the {,un}map_pirq hypercalls so interrupts can be
assigned a pIRQ handler that can then be used by further hypercalls to
bind the interrupt to a domain.

Note that the {,un}map_pirq hypercalls end up calling helpers that are
already used against a PVH domain in order to setup interrupts for the
hardware domain when running in PVH mode.  physdev_map_pirq() will
call allocate_and_map_{gsi,msi}_pirq() which is already used by the
vIO-APIC or the vPCI code respectively.  So the exposed code paths are
not new when targeting a PVH domain, but rather previous callers are
not hypercall but emulation based.

Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
---
v14->v15 changes:
Change to use the commit message wrote by Roger.

v13->v14 changes:
Modified the commit message.

v12->v13 changes:
Removed the PHYSDEVOP_(un)map_pirq restriction check for pvh domU and added a 
corresponding description in the commit message.

v11->v12 changes:
Avoid using return, set error code instead when (un)map is not allowed.

v10->v11 changes:
Delete the judgment of "d==currd", so that we can prevent physdev_(un)map_pirq 
from being executed when domU has no pirq, instead of just preventing 
self-mapping.
And modify the description of the commit message accordingly.

v9->v10 changes:
Indent the comments above PHYSDEVOP_map_pirq according to the code style.

v8->v9 changes:
Add a comment above PHYSDEVOP_map_pirq to describe why need this hypercall.
Change "!is_pv_domain(d)" to "is_hvm_domain(d)", and "map.domid == DOMID_SELF" 
to "d == current->domian".

v7->v8 changes:
Add the domid check(domid == DOMID_SELF) to prevent self map when guest doesn't 
use pirq.
That check was missed in the previous version.

v6->v7 changes:
Nothing.

v5->v6 changes:
Nothing.

v4->v5 changes:
Move the check of self map_pirq to physdev.c, and change to check if the caller 
has PIRQ flag, and just break for PHYSDEVOP_(un)map_pirq in hvm_physdev_op.

v3->v4 changes:
add check to prevent PVH self map.

v2->v3 changes:
Du to changes in the implementation of the second patch on kernel side(that it 
will do setup_gsi and map_pirq when assigning a device to passthrough), add 
PHYSDEVOP_setup_gsi for PVH dom0, and we need to support self mapping.
---
 xen/arch/x86/hvm/hypercall.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/x86/hvm/hypercall.c b/xen/arch/x86/hvm/hypercall.c
index f023f7879e24..81883c8d4f60 100644
--- a/xen/arch/x86/hvm/hypercall.c
+++ b/xen/arch/x86/hvm/hypercall.c
@@ -73,6 +73,8 @@ long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
     {
     case PHYSDEVOP_map_pirq:
     case PHYSDEVOP_unmap_pirq:
+        break;
+
     case PHYSDEVOP_eoi:
     case PHYSDEVOP_irq_status_query:
     case PHYSDEVOP_get_free_pirq:
-- 
2.34.1