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Message-ID: <ZZY96U3CzvDhu3BL@LeoBras>
Date: Thu, 4 Jan 2024 02:11:05 -0300
From: Leonardo Bras <leobras@...hat.com>
To: guoren@...nel.org
Cc: Leonardo Bras <leobras@...hat.com>,
paul.walmsley@...ive.com,
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linux-riscv@...ts.infradead.org,
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Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V12 08/14] riscv: qspinlock: Force virt_spin_lock for KVM guests
On Mon, Dec 25, 2023 at 07:58:41AM -0500, guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.alibaba.com>
>
> Force to enable virt_spin_lock when KVM guest, because fair locks
> have horrible lock 'holder' preemption issues.
>
> Suggested-by: Leonardo Bras <leobras@...hat.com>
> Link: https://lkml.kernel.org/kvm/ZQK9-tn2MepXlY1u@redhat.com/
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> ---
> 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@...hat.com>
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