[PATCH] kvmtool: arm64: Report missing support for 32bit guests

[Suzuki K Poulose]

When the host doesn't support 32bit guests, the kvmtool fails
without a proper message on what is wrong. i.e,

 $ lkvm run -c 1 Image --aarch32
  # lkvm run -k Image -m 256 -c 1 --name guest-105618
  Fatal: Unable to initialise vcpu

Given that there is no other easy way to check if the host supports 32bit
guests, it is always good to report this by checking the capability, rather
than leaving the users to hunt this down by looking at the code!

After this patch:

 $ lkvm run -c 1 Image --aarch32
  # lkvm run -k Image -m 256 -c 1 --name guest-105695
  Fatal: 32bit guests are not supported

Cc: Will Deacon <will at kernel.org>
Reported-by: Sami Mujawar <sami.mujawar at arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose at arm.com>
---
 arm/kvm-cpu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
index 554414f..2acecae 100644
--- a/arm/kvm-cpu.c
+++ b/arm/kvm-cpu.c
@@ -46,6 +46,10 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
 		.features = ARM_VCPU_FEATURE_FLAGS(kvm, cpu_id)
 	};
 
+	if (kvm->cfg.arch.aarch32_guest &&
+	    !kvm__supports_extension(kvm, KVM_CAP_ARM_EL1_32BIT))
+		die("32bit guests are not supported\n");
+
 	vcpu = calloc(1, sizeof(struct kvm_cpu));
 	if (!vcpu)
 		return NULL;
-- 
2.24.1