arm64: Rework set_pmu_attr()

By the time kvmtool generates the DTB node for the PMU, the
KVM_ARM_VCPU_PMU_V3 VCPU feature is already set by kvm_cpu__arch_init().

KVM refuses to run a VCPU if the PMU hasn't been initialized. A PMU
cannot be initialized if the interrupt ID hasn't been set by userspace.
As a consequence, kvmtool will get an error if the interrupt ID or if
the PMU has not been initialized:

KVM_RUN failed: Invalid argument

To make debugging easier, exit with an error message as soon as one the
PMU ioctls fails, instead of waiting until the VCPU is first run.

To avoid the repetition of assigning a new kvm_device_attr struct in the
main body of pmu__generate_fdt_nodes(), which hinders readability of the
function, move the struct to set_pmu_attr().

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20220412133231.35355-8-alexandru.elisei@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 16 insertions, 32 deletions

diff --git a/arm/aarch64/pmu.c b/arm/aarch64/pmu.c
index 6b190c5e..ac5b7bcd 100644
--- a/arm/aarch64/pmu.c
+++ b/arm/aarch64/pmu.c
@@ -7,30 +7,31 @@
 
 #include "asm/pmu.h"
 
-static int set_pmu_attr(struct kvm *kvm, int vcpu_idx,
-			struct kvm_device_attr *attr)
+static void set_pmu_attr(struct kvm_cpu *vcpu, void *addr, u64 attr)
 {
-	int ret, fd;
-
-	fd = kvm->cpus[vcpu_idx]->vcpu_fd;
+	struct kvm_device_attr pmu_attr = {
+		.group	= KVM_ARM_VCPU_PMU_V3_CTRL,
+		.addr	= (u64)addr,
+		.attr	= attr,
+	};
+	int ret;
 
-	ret = ioctl(fd, KVM_HAS_DEVICE_ATTR, attr);
+	ret = ioctl(vcpu->vcpu_fd, KVM_HAS_DEVICE_ATTR, &pmu_attr);
 	if (!ret) {
-		ret = ioctl(fd, KVM_SET_DEVICE_ATTR, attr);
+		ret = ioctl(vcpu->vcpu_fd, KVM_SET_DEVICE_ATTR, &pmu_attr);
 		if (ret)
-			perror("PMU KVM_SET_DEVICE_ATTR failed");
+			die_perror("PMU KVM_SET_DEVICE_ATTR");
 	} else {
-		pr_err("Unsupported PMU on vcpu%d\n", vcpu_idx);
+		die_perror("PMU KVM_HAS_DEVICE_ATTR");
 	}
-
-	return ret;
 }
 
 void pmu__generate_fdt_nodes(void *fdt, struct kvm *kvm)
 {
 	const char compatible[] = "arm,armv8-pmuv3";
 	int irq = KVM_ARM_PMUv3_PPI;
-	int i, ret;
+	struct kvm_cpu *vcpu;
+	int i;
 
 	u32 cpu_mask = (((1 << kvm->nrcpus) - 1) << GIC_FDT_IRQ_PPI_CPU_SHIFT) \
 		       & GIC_FDT_IRQ_PPI_CPU_MASK;
@@ -44,26 +45,9 @@ void pmu__generate_fdt_nodes(void *fdt, struct kvm *kvm)
 		return;
 
 	for (i = 0; i < kvm->nrcpus; i++) {
-		struct kvm_device_attr pmu_attr;
-
-		pmu_attr = (struct kvm_device_attr){
-			.group	= KVM_ARM_VCPU_PMU_V3_CTRL,
-			.addr	= (u64)(unsigned long)&irq,
-			.attr	= KVM_ARM_VCPU_PMU_V3_IRQ,
-		};
-
-		ret = set_pmu_attr(kvm, i, &pmu_attr);
-		if (ret)
-			return;
-
-		pmu_attr = (struct kvm_device_attr){
-			.group	= KVM_ARM_VCPU_PMU_V3_CTRL,
-			.attr	= KVM_ARM_VCPU_PMU_V3_INIT,
-		};
-
-		ret = set_pmu_attr(kvm, i, &pmu_attr);
-		if (ret)
-			return;
+		vcpu = kvm->cpus[i];
+		set_pmu_attr(vcpu, &irq, KVM_ARM_VCPU_PMU_V3_IRQ);
+		set_pmu_attr(vcpu, NULL, KVM_ARM_VCPU_PMU_V3_INIT);
 	}
 
 	_FDT(fdt_begin_node(fdt, "pmu"));