xen/pvh: Piggyback on PVHVM for event channels (v2)

PVH is a PV guest with a twist - there are certain things
that work in it like HVM and some like PV. There is
a similar mode - PVHVM where we run in HVM mode with
PV code enabled - and this patch explores that.

The most notable PV interfaces are the XenBus and event channels.

We will piggyback on how the event channel mechanism is
used in PVHVM - that is we want the normal native IRQ mechanism
and we will install a vector (hvm callback) for which we
will call the event channel mechanism.

This means that from a pvops perspective, we can use
native_irq_ops instead of the Xen PV specific. Albeit in the
future we could support pirq_eoi_map. But that is
a feature request that can be shared with PVHVM.

Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

2 files changed, 7 insertions, 3 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 2eca6187fc92..a4e2f30917a3 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1144,8 +1144,9 @@ void xen_setup_vcpu_info_placement(void)
                 xen_vcpu_setup(cpu);
 
         /* xen_vcpu_setup managed to place the vcpu_info within the
-           percpu area for all cpus, so make use of it */
-        if (have_vcpu_info_placement) {
+         * percpu area for all cpus, so make use of it. Note that for
+         * PVH we want to use native IRQ mechanism. */
+        if (have_vcpu_info_placement && !xen_pvh_domain()) {
                 pv_irq_ops.save_fl = __PV_IS_CALLEE_SAVE(xen_save_fl_direct);
                 pv_irq_ops.restore_fl = __PV_IS_CALLEE_SAVE(xen_restore_fl_direct);
                 pv_irq_ops.irq_disable = __PV_IS_CALLEE_SAVE(xen_irq_disable_direct);
diff --git a/arch/x86/xen/irq.c b/arch/x86/xen/irq.c
index 0da7f863056f..76ca326105f7 100644
--- a/arch/x86/xen/irq.c
+++ b/arch/x86/xen/irq.c
@@ -5,6 +5,7 @@
 #include <xen/interface/xen.h>
 #include <xen/interface/sched.h>
 #include <xen/interface/vcpu.h>
+#include <xen/features.h>
 #include <xen/events.h>
 
 #include <asm/xen/hypercall.h>
@@ -128,6 +129,8 @@ static const struct pv_irq_ops xen_irq_ops __initconst = {
 
 void __init xen_init_irq_ops(void)
 {
-        pv_irq_ops = xen_irq_ops;
+        /* For PVH we use default pv_irq_ops settings. */
+        if (!xen_feature(XENFEAT_hvm_callback_vector))
+                pv_irq_ops = xen_irq_ops;
         x86_init.irqs.intr_init = xen_init_IRQ;
 }