riscv: kvm: return SBI_ERR_FAILURE for pmu_event_info() when OOM

kvm_riscv_vcpu_pmu_event_info() returned -ENOMEM from the
SBI extension handler, which caused kvm_riscv_vcpu_sbi_ecall()
to abort KVM_RUN and surface the error to userspace instead of
completing the ECALL with a negative SBI error in a0.
Use SBI_ERR_FAILURE and the normal retdata path, matching other PMU
handlers and kvm_sbi_ext_pmu_handler comment.

Fixes: e309fd1 ("RISC-V: KVM: Implement get event info function")
Cc: stable@vger.kernel.org
Signed-off-by: Osama Abdelkader <osama.abdelkader@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260514173642.41448-2-osama.abdelkader@gmail.com
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: osamakader

arch/riscv/kvm/vcpu_pmu.c

@@ -501,8 +501,10 @@ int kvm_riscv_vcpu_pmu_event_info(struct kvm_vcpu *vcpu, unsigned long saddr_low
 	}
 
 	einfo = kzalloc(shmem_size, GFP_KERNEL);
-	if (!einfo)
-		return -ENOMEM;
+	if (!einfo) {
+		ret = SBI_ERR_FAILURE;
+		goto out;
+	}
 
 	ret = kvm_vcpu_read_guest(vcpu, shmem, einfo, shmem_size);
 	if (ret) {