[PULL v2 49/86] target/i386: Fix sanity check on max APIC ID / X2APIC enablement

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

From: David Woodhouse <dwmw2@xxxxxxxxxxxxx>

The check on x86ms->apic_id_limit in pc_machine_done() had two problems.

Firstly, we need KVM to support the X2APIC API in order to allow IRQ
delivery to APICs >= 255. So we need to call/check kvm_enable_x2apic(),
which was done elsewhere in *some* cases but not all.

Secondly, microvm needs the same check. So move it from pc_machine_done()
to x86_cpus_init() where it will work for both.

The check in kvm_cpu_instance_init() is now redundant and can be dropped.

Signed-off-by: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Acked-by: Claudio Fontana <cfontana@xxxxxxx>
Message-Id: <20220314142544.150555-1-dwmw2@xxxxxxxxxxxxx>
Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 hw/i386/pc.c              |  8 --------
 hw/i386/x86.c             | 16 ++++++++++++++++
 target/i386/kvm/kvm-cpu.c |  2 +-
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 312eb9e400..15f37d8dc6 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -744,14 +744,6 @@ void pc_machine_done(Notifier *notifier, void *data)
         /* update FW_CFG_NB_CPUS to account for -device added CPUs */
         fw_cfg_modify_i16(x86ms->fw_cfg, FW_CFG_NB_CPUS, x86ms->boot_cpus);
     }
-
-
-    if (x86ms->apic_id_limit > 255 && !xen_enabled() &&
-        !kvm_irqchip_in_kernel()) {
-        error_report("current -smp configuration requires kernel "
-                     "irqchip support.");
-        exit(EXIT_FAILURE);
-    }
 }
 
 void pc_guest_info_init(PCMachineState *pcms)
diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index 79ebdface6..f79e720cc2 100644
--- a/hw/i386/x86.c
+++ b/hw/i386/x86.c
@@ -38,6 +38,7 @@
 #include "sysemu/replay.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/cpu-timers.h"
+#include "sysemu/xen.h"
 #include "trace.h"
 
 #include "hw/i386/x86.h"
@@ -122,6 +123,21 @@ void x86_cpus_init(X86MachineState *x86ms, int default_cpu_version)
      */
     x86ms->apic_id_limit = x86_cpu_apic_id_from_index(x86ms,
                                                       ms->smp.max_cpus - 1) + 1;
+
+    /*
+     * Can we support APIC ID 255 or higher?
+     *
+     * Under Xen: yes.
+     * With userspace emulated lapic: no
+     * With KVM's in-kernel lapic: only if X2APIC API is enabled.
+     */
+    if (x86ms->apic_id_limit > 255 && !xen_enabled() &&
+        (!kvm_irqchip_in_kernel() || !kvm_enable_x2apic())) {
+        error_report("current -smp configuration requires kernel "
+                     "irqchip and X2APIC API support.");
+        exit(EXIT_FAILURE);
+    }
+
     possible_cpus = mc->possible_cpu_arch_ids(ms);
     for (i = 0; i < ms->smp.cpus; i++) {
         x86_cpu_new(x86ms, possible_cpus->cpus[i].arch_id, &error_fatal);
diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
index 5eb955ce9a..7237378a7d 100644
--- a/target/i386/kvm/kvm-cpu.c
+++ b/target/i386/kvm/kvm-cpu.c
@@ -171,7 +171,7 @@ static void kvm_cpu_instance_init(CPUState *cs)
         /* only applies to builtin_x86_defs cpus */
         if (!kvm_irqchip_in_kernel()) {
             x86_cpu_change_kvm_default("x2apic", "off");
-        } else if (kvm_irqchip_is_split() && kvm_enable_x2apic()) {
+        } else if (kvm_irqchip_is_split()) {
             x86_cpu_change_kvm_default("kvm-msi-ext-dest-id", "on");
         }
 
-- 
MST