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Re: [PATCH 1/1] target/riscv/kvm.c: Fix the hart bit setting of AIA
From: |
Alistair Francis |
Subject: |
Re: [PATCH 1/1] target/riscv/kvm.c: Fix the hart bit setting of AIA |
Date: |
Mon, 29 Apr 2024 13:25:11 +1000 |
On Mon, Apr 15, 2024 at 4:53 PM Yong-Xuan Wang <yongxuan.wang@sifive.com> wrote:
>
> 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.
I don't really follow this.
Do you mind re-wording it to talk about what the specification says?
Not what Linux does.
>
> [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--;
Assuming there are an even number of cores (which there usually are)
won't this always result in a
> + hart_bits = find_last_bit(&max_hart_per_socket, BITS_PER_LONG) + 1;
1 being returned by find_last_bit()?
Alistair
> + } 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
>
>