From e3a7ec839fa4f823666d726989c375dcf73348a4 Mon Sep 17 00:00:00 2001
From: Ying Fang <fangying1@huawei.com>
Date: Wed, 15 Apr 2020 16:14:50 +0800
Subject: [PATCH] ARM: KVM: Check KVM_CAP_ARM_IRQ_LINE_LAYOUT_2 for smp_cpus >
 256
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Host kernel within [4.18, 5.3] report an erroneous KVM_MAX_VCPUS=512
for ARM. The actual capability to instantiate more than 256 vcpus
was fixed in 5.4 with the upgrade of the KVM_IRQ_LINE ABI to support
vcpu id encoded on 12 bits instead of 8 and a redistributor consuming
a single KVM IO device instead of 2.

So let's check this capability when attempting to use more than 256
vcpus within any ARM kvm accelerated machine.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Message-id: 20191003154640.22451-4-eric.auger@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry-picked from commit fff9f5558d0e0813d4f80bfe1602acf225eca4fd)
[yu: Use the legacy smp_cpus instead of ms->smp.cpus, as we don't have
    ¦struct CpuTopology in MachineState at that time. See commit
    ¦edeeec911702 for details.]
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 target/arm/kvm.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 50e86f8b..cc7a46df 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -173,6 +173,8 @@ int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
 
 int kvm_arch_init(MachineState *ms, KVMState *s)
 {
+    int ret = 0;
+    unsigned int smp_cpus = ms->smp.cpus;
     /* For ARM interrupt delivery is always asynchronous,
      * whether we are using an in-kernel VGIC or not.
      */
@@ -186,7 +188,14 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
 
     cap_has_mp_state = kvm_check_extension(s, KVM_CAP_MP_STATE);
 
-    return 0;
+    if (smp_cpus > 256 &&
+        !kvm_check_extension(s, KVM_CAP_ARM_IRQ_LINE_LAYOUT_2)) {
+        error_report("Using more than 256 vcpus requires a host kernel "
+                     "with KVM_CAP_ARM_IRQ_LINE_LAYOUT_2");
+        ret = -EINVAL;
+    }
+
+    return ret;
 }
 
 unsigned long kvm_arch_vcpu_id(CPUState *cpu)
-- 
2.23.0