From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> Add a static key controlling whether virt_spin_lock() should be called or not. When running on bare metal set the new key to false. The KVM guests fall back to a Test-and-Set spinlock, because fair locks have horrible lock 'holder' preemption issues. The virt_spin_lock_key would shortcut for the queued_spin_lock_slowpath() function that allow virt_spin_lock to hijack it. Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx> --- arch/riscv/Kconfig | 1 + arch/riscv/include/asm/sbi.h | 8 ++++++++ arch/riscv/include/asm/spinlock.h | 22 ++++++++++++++++++++++ arch/riscv/kernel/cpufeature.c | 4 +++- arch/riscv/kernel/sbi.c | 2 +- arch/riscv/kernel/setup.c | 19 +++++++++++++++++++ 6 files changed, 54 insertions(+), 2 deletions(-) diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 119e774a3dcf..42ae45c42b4d 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -20,6 +20,7 @@ config RISCV select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE select ARCH_HAS_BINFMT_FLAT select ARCH_HAS_CURRENT_STACK_POINTER + select ARCH_HAS_CPU_FINALIZE_INIT select ARCH_HAS_DEBUG_VIRTUAL if MMU select ARCH_HAS_DEBUG_VM_PGTABLE select ARCH_HAS_DEBUG_WX diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h index e1523c8624cc..b7ced34b79a3 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, }; @@ -286,6 +293,7 @@ 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/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h index 9eb3ad31e564..13f3e14500c0 100644 --- a/arch/riscv/include/asm/spinlock.h +++ b/arch/riscv/include/asm/spinlock.h @@ -4,6 +4,28 @@ #define __ASM_RISCV_SPINLOCK_H #ifdef CONFIG_QUEUED_SPINLOCKS +/* + * The KVM guests fall back to a Test-and-Set spinlock, because fair locks + * have horrible lock 'holder' preemption issues. The virt_spin_lock_key + * would shortcut for the queued_spin_lock_slowpath() function that allow + * virt_spin_lock to hijack it. + */ +DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); + +#define virt_spin_lock virt_spin_lock +static inline bool virt_spin_lock(struct qspinlock *lock) +{ + if (!static_branch_likely(&virt_spin_lock_key)) + return false; + + do { + while (atomic_read(&lock->val) != 0) + cpu_relax(); + } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0); + + return true; +} + #define _Q_PENDING_LOOPS (1 << 9) #endif diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index d9694fe40a9a..26826aa590e9 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -21,6 +21,7 @@ #include <asm/hwcap.h> #include <asm/patch.h> #include <asm/processor.h> +#include <asm/sbi.h> #include <asm/vector.h> #define NUM_ALPHA_EXTS ('z' - 'a' + 1) @@ -343,7 +344,8 @@ void __init riscv_fill_hwcap(void) * ticket_spinlock, but can not be vice. */ if (!force_qspinlock && - !riscv_has_errata_thead_qspinlock()) { + !riscv_has_errata_thead_qspinlock() && + (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM)) { set_bit(RISCV_ISA_EXT_XTICKETLOCK, isainfo->isa); } #endif diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c index c672c8ba9a2a..398b768a02e6 100644 --- a/arch/riscv/kernel/sbi.c +++ b/arch/riscv/kernel/sbi.c @@ -555,7 +555,7 @@ 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 971fe776e2f8..def89fd8ea55 100644 --- a/arch/riscv/kernel/setup.c +++ b/arch/riscv/kernel/setup.c @@ -26,6 +26,7 @@ #include <asm/alternative.h> #include <asm/cacheflush.h> #include <asm/cpu_ops.h> +#include <asm/cpufeature.h> #include <asm/early_ioremap.h> #include <asm/pgtable.h> #include <asm/setup.h> @@ -264,6 +265,19 @@ static void __init parse_dtb(void) #endif } +#ifdef CONFIG_QUEUED_SPINLOCKS +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 || + force_qspinlock) + static_branch_disable(&virt_spin_lock_key); +} +#else +static void __init virt_spin_lock_init(void) {} +#endif + extern void __init init_rt_signal_env(void); void __init setup_arch(char **cmdline_p) @@ -313,6 +327,11 @@ void __init setup_arch(char **cmdline_p) riscv_noncoherent_supported(); } +void __init arch_cpu_finalize_init(void) +{ + virt_spin_lock_init(); +} + static int __init topology_init(void) { int i, ret; -- 2.36.1