[PATCH] firmware: Fix vcpu hotplug race with qemu-xen

[Anthony PERARD <anthony.perard@citrix.com>]

When hotplugging more than one vcpu, some of those vcpus might not be
seen as plugged by the guest.

By using edged-triggered General-Purpose Event instead of a
level-triggered GPE, the race is avoided. This is in sync with how a
different QEMU guest is handeling CPU hotplug event.

There is more information about why in SeaBIOS's commit
9c6635bd48d39a1d17d0a73df6e577ef6bd0037c.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 tools/firmware/hvmloader/acpi/mk_dsdt.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/firmware/hvmloader/acpi/mk_dsdt.c b/tools/firmware/hvmloader/acpi/mk_dsdt.c
index 996f30b..ecbe4cd 100644
--- a/tools/firmware/hvmloader/acpi/mk_dsdt.c
+++ b/tools/firmware/hvmloader/acpi/mk_dsdt.c
@@ -220,9 +220,13 @@ int main(int argc, char **argv)
 
     pop_block();
 
-    /* Define GPE control method '_L02'. */
+    /* Define GPE control method. */
     push_block("Scope", "\\_GPE");
-    push_block("Method", "_L02");
+    if (dm_version == QEMU_XEN) {
+        push_block("Method", "_E02");
+    } else {
+        push_block("Method", "_L02");
+    }
     stmt("Return", "\\_SB.PRSC()");
     pop_block();
     pop_block();
-- 
Anthony PERARD