[PATCH 1/1] target/riscv/kvm.c: Fix the hart bit setting of AIA

[Yong-Xuan Wang]

The hart bit setting is different with Linux AIA driver[1] when the number
of hart is power of 2. For example, when the guest has 4 harts, the
estimated result of AIA driver is 2, whereas we pass 3 to RISC-V/KVM. Since
only 2 bits are needed to represent 4 harts, update the formula to get the
accurate result.

[1] https://lore.kernel.org/all/20240307140307.646078-1-apatel@ventanamicro.com/

Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
---
 target/riscv/kvm/kvm-cpu.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index 6a6c6cae80f1..388c4ddaa145 100644
--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -1642,7 +1642,14 @@ void kvm_riscv_aia_create(MachineState *machine, 
uint64_t group_shift,
         }
     }
 
-    hart_bits = find_last_bit(&max_hart_per_socket, BITS_PER_LONG) + 1;
+
+    if (max_hart_per_socket > 1) {
+        max_hart_per_socket--;
+        hart_bits = find_last_bit(&max_hart_per_socket, BITS_PER_LONG) + 1;
+    } else {
+        hart_bits = 0;
+    }
+
     ret = kvm_device_access(aia_fd, KVM_DEV_RISCV_AIA_GRP_CONFIG,
                             KVM_DEV_RISCV_AIA_CONFIG_HART_BITS,
                             &hart_bits, true, NULL);
-- 
2.17.1