kvm/i386: Add xen-evtchn-max-pirq property

The default number of PIRQs is set to 256 to avoid issues with 32-bit MSI
devices. Allow it to be increased if the user desires.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

1 files changed, 11 insertions, 10 deletions

diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c
index 69c0204d4f..886fbf6b3b 100644
--- a/hw/i386/kvm/xen_evtchn.c
+++ b/hw/i386/kvm/xen_evtchn.c
@@ -302,17 +302,18 @@ void xen_evtchn_create(void)
     }
 
     /*
-     * We could parameterise the number of PIRQs available if needed,
-     * but for now limit it to 256. The Xen scheme for encoding PIRQ#
-     * into an MSI message is not compatible with 32-bit MSI, as it
-     * puts the high bits of the PIRQ# into the high bits of the MSI
-     * message address, instead of using the Extended Destination ID
-     * in address bits 4-11 which perhaps would have been a better
-     * choice. So to keep life simple, just stick with 256 as the
-     * default, which conveniently doesn't need to set anything
-     * outside the low 32 bits of the address.
+     * The Xen scheme for encoding PIRQ# into an MSI message is not
+     * compatible with 32-bit MSI, as it puts the high bits of the
+     * PIRQ# into the high bits of the MSI message address, instead of
+     * using the Extended Destination ID in address bits 4-11 which
+     * perhaps would have been a better choice.
+     *
+     * To keep life simple, kvm_accel_instance_init() initialises the
+     * default to 256. which conveniently doesn't need to set anything
+     * outside the low 32 bits of the address. It can be increased by
+     * setting the xen-evtchn-max-pirq property.
      */
-    s->nr_pirqs = 256;
+    s->nr_pirqs = kvm_xen_get_evtchn_max_pirq();
 
     s->nr_pirq_inuse_words = DIV_ROUND_UP(s->nr_pirqs, 64);
     s->pirq_inuse_bitmap = g_new0(uint64_t, s->nr_pirq_inuse_words);