Re: [PATCH V12 08/14] riscv: qspinlock: Force virt_spin_lock for KVM guests

[Leonardo Bras]

On Mon, Dec 25, 2023 at 07:58:41AM -0500, guoren@xxxxxxxxxx wrote:
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> 
> Force to enable virt_spin_lock when KVM guest, because fair locks
> have horrible lock 'holder' preemption issues.
> 
> Suggested-by: Leonardo Bras <leobras@xxxxxxxxxx>
> Link: https://lkml.kernel.org/kvm/ZQK9-tn2MepXlY1u@xxxxxxxxxx/
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> ---
>  arch/riscv/include/asm/sbi.h | 8 ++++++++
>  arch/riscv/kernel/sbi.c      | 2 +-
>  arch/riscv/kernel/setup.c    | 6 +++++-
>  3 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> index 0892f4421bc4..8f748d9e1b85 100644
> --- a/arch/riscv/include/asm/sbi.h
> +++ b/arch/riscv/include/asm/sbi.h
> @@ -51,6 +51,13 @@ enum sbi_ext_base_fid {
>  	SBI_EXT_BASE_GET_MIMPID,
>  };
>  
> +enum sbi_ext_base_impl_id {
> +	SBI_EXT_BASE_IMPL_ID_BBL = 0,
> +	SBI_EXT_BASE_IMPL_ID_OPENSBI,
> +	SBI_EXT_BASE_IMPL_ID_XVISOR,
> +	SBI_EXT_BASE_IMPL_ID_KVM,
> +};
> +
>  enum sbi_ext_time_fid {
>  	SBI_EXT_TIME_SET_TIMER = 0,
>  };
> @@ -276,6 +283,7 @@ int sbi_console_getchar(void);
>  long sbi_get_mvendorid(void);
>  long sbi_get_marchid(void);
>  long sbi_get_mimpid(void);
> +long sbi_get_firmware_id(void);
>  void sbi_set_timer(uint64_t stime_value);
>  void sbi_shutdown(void);
>  void sbi_send_ipi(unsigned int cpu);
> diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> index 5a62ed1da453..4330aedf65fd 100644
> --- a/arch/riscv/kernel/sbi.c
> +++ b/arch/riscv/kernel/sbi.c
> @@ -543,7 +543,7 @@ static inline long sbi_get_spec_version(void)
>  	return __sbi_base_ecall(SBI_EXT_BASE_GET_SPEC_VERSION);
>  }
>  
> -static inline long sbi_get_firmware_id(void)
> +long sbi_get_firmware_id(void)
>  {
>  	return __sbi_base_ecall(SBI_EXT_BASE_GET_IMP_ID);
>  }
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 0bafb9fd6ea3..e33430e9d97e 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -281,6 +281,9 @@ DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
>  
>  static void __init virt_spin_lock_init(void)
>  {
> +	if (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM)
> +		no_virt_spin = true;
> +
>  	if (no_virt_spin)
>  		static_branch_disable(&virt_spin_lock_key);
>  	else
> @@ -290,7 +293,8 @@ static void __init virt_spin_lock_init(void)
>  
>  static void __init riscv_spinlock_init(void)
>  {
> -	if (!enable_qspinlock) {
> +	if ((!enable_qspinlock) &&
> +	    (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM)) {
>  		static_branch_disable(&combo_qspinlock_key);
>  		pr_info("Ticket spinlock: enabled\n");
>  	} else {
> -- 
> 2.40.1
> 

LGTM:
Reviewed-by: Leonardo Bras <leobras@xxxxxxxxxx>