arm: Fail early if KVM_CAP_ARM_PMU_V3 is not supported

pmu__generate_fdt_nodes() checks if the host has support for PMU in a guest
and prints a warning if that's not the case. However, this check is too
late because the function is called after the VCPU has been created, and
VCPU creation fails if KVM_CAP_ARM_PMU_V3 is not available with a rather
unhelpful error:

$ ./vm run -c1 -m64 -f selftest.flat --pmu
  # lkvm run --firmware selftest.flat -m 64 -c 1 --name guest-1039
  Info: Placing fdt at 0x80200000 - 0x80210000
  Fatal: Unable to initialise vcpu

Move the check for KVM_CAP_ARM_PMU_V3 to kvm_cpu__arch_init() before the
VCPU is created so the user can get a more useful error message. This
also matches the behaviour of KVM_CAP_ARM_EL1_32BIT.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20210415131725.105675-1-alexandru.elisei@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

2 files changed, 4 insertions, 5 deletions

diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
index 2acecaec..6a2408c6 100644
--- a/arm/kvm-cpu.c
+++ b/arm/kvm-cpu.c
@@ -50,6 +50,10 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
 	    !kvm__supports_extension(kvm, KVM_CAP_ARM_EL1_32BIT))
 		die("32bit guests are not supported\n");
 
+	if (kvm->cfg.arch.has_pmuv3 &&
+	    !kvm__supports_extension(kvm, KVM_CAP_ARM_PMU_V3))
+		die("PMUv3 is not supported");
+
 	vcpu = calloc(1, sizeof(struct kvm_cpu));
 	if (!vcpu)
 		return NULL;
diff --git a/arm/pmu.c b/arm/pmu.c
index ffd152e2..5b058eab 100644
--- a/arm/pmu.c
+++ b/arm/pmu.c
@@ -43,11 +43,6 @@ void pmu__generate_fdt_nodes(void *fdt, struct kvm *kvm)
 	if (!kvm->cfg.arch.has_pmuv3)
 		return;
 
-	if (!kvm__supports_extension(kvm, KVM_CAP_ARM_PMU_V3)) {
-		pr_info("PMU unsupported\n");
-		return;
-	}
-
 	for (i = 0; i < kvm->nrcpus; i++) {
 		struct kvm_device_attr pmu_attr;