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([2a02:6b6a:b4d7:0:c7c:f931:dd4c:1ea6]) by smtp.gmail.com with ESMTPSA id h4-20020adff184000000b00236e9755c02sm2494568wro.111.2022.11.03.23.24.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 03 Nov 2022 23:24:13 -0700 (PDT) Message-ID: <1b404477-8bff-0d33-477f-514e12ba8546@bytedance.com> Date: Fri, 4 Nov 2022 06:24:13 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [External] Re: [RFC 5/6] KVM: arm64: Support the VCPU preemption check Content-Language: en-US To: Steven Price , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-doc@vger.kernel.org, virtualization@lists.linux-foundation.org, linux@armlinux.org.uk, yezengruan@huawei.com, catalin.marinas@arm.com, will@kernel.org, maz@kernel.org, mark.rutland@arm.com Cc: fam.zheng@bytedance.com, liangma@liangbit.com, punit.agrawal@bytedance.com References: <20221102161340.2982090-1-usama.arif@bytedance.com> <20221102161340.2982090-6-usama.arif@bytedance.com> <76f59579-b701-a243-2a50-72a1401d3a65@arm.com> From: Usama Arif In-Reply-To: <76f59579-b701-a243-2a50-72a1401d3a65@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/11/2022 13:25, Steven Price wrote: > On 02/11/2022 16:13, Usama Arif wrote: >> Support the vcpu_is_preempted() functionality under KVM/arm64. This will >> enhance lock performance on overcommitted hosts (more runnable VCPUs >> than physical CPUs in the system) as doing busy waits for preempted >> VCPUs will hurt system performance far worse than early yielding. >> >> Signed-off-by: Zengruan Ye >> Signed-off-by: Usama Arif >> --- >> arch/arm64/include/asm/paravirt.h | 2 + >> arch/arm64/include/asm/spinlock.h | 16 +++- >> arch/arm64/kernel/paravirt.c | 126 ++++++++++++++++++++++++++++++ >> arch/arm64/kernel/setup.c | 3 + >> include/linux/cpuhotplug.h | 1 + >> 5 files changed, 147 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/include/asm/paravirt.h b/arch/arm64/include/asm/paravirt.h >> index 9aa193e0e8f2..4ccb4356c56b 100644 >> --- a/arch/arm64/include/asm/paravirt.h >> +++ b/arch/arm64/include/asm/paravirt.h >> @@ -19,10 +19,12 @@ static inline u64 paravirt_steal_clock(int cpu) >> } >> >> int __init pv_time_init(void); >> +int __init pv_lock_init(void); >> >> #else >> >> #define pv_time_init() do {} while (0) >> +#define pv_lock_init() do {} while (0) >> >> #endif // CONFIG_PARAVIRT >> >> diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h >> index 0525c0b089ed..7023efa4de96 100644 >> --- a/arch/arm64/include/asm/spinlock.h >> +++ b/arch/arm64/include/asm/spinlock.h >> @@ -10,7 +10,20 @@ >> >> /* See include/linux/spinlock.h */ >> #define smp_mb__after_spinlock() smp_mb() >> +#define vcpu_is_preempted vcpu_is_preempted >> + >> +#ifdef CONFIG_PARAVIRT >> +#include >> + >> +bool dummy_vcpu_is_preempted(int cpu); >> >> +DECLARE_STATIC_CALL(pv_vcpu_is_preempted, dummy_vcpu_is_preempted); >> +static inline bool vcpu_is_preempted(int cpu) >> +{ >> + return static_call(pv_vcpu_is_preempted)(cpu); >> +} >> + >> +#else >> /* >> * Changing this will break osq_lock() thanks to the call inside >> * smp_cond_load_relaxed(). >> @@ -18,10 +31,11 @@ >> * See: >> * https://lore.kernel.org/lkml/20200110100612.GC2827@hirez.programming.kicks-ass.net >> */ >> -#define vcpu_is_preempted vcpu_is_preempted >> static inline bool vcpu_is_preempted(int cpu) >> { >> return false; >> } >> >> +#endif /* CONFIG_PARAVIRT */ >> + >> #endif /* __ASM_SPINLOCK_H */ >> diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c >> index 57c7c211f8c7..45bcca87bed7 100644 >> --- a/arch/arm64/kernel/paravirt.c >> +++ b/arch/arm64/kernel/paravirt.c >> @@ -22,6 +22,7 @@ >> >> #include >> #include >> +#include >> #include >> >> struct static_key paravirt_steal_enabled; >> @@ -38,7 +39,12 @@ struct pv_time_stolen_time_region { >> struct pvclock_vcpu_stolen_time __rcu *kaddr; >> }; >> >> +struct pv_lock_state_region { >> + struct pvlock_vcpu_state __rcu *kaddr; >> +}; >> + >> static DEFINE_PER_CPU(struct pv_time_stolen_time_region, stolen_time_region); >> +static DEFINE_PER_CPU(struct pv_lock_state_region, lock_state_region); >> >> static bool steal_acc = true; >> static int __init parse_no_stealacc(char *arg) >> @@ -178,3 +184,123 @@ int __init pv_time_init(void) >> >> return 0; >> } >> + >> +static bool native_vcpu_is_preempted(int cpu) >> +{ >> + return false; >> +} >> + >> +DEFINE_STATIC_CALL(pv_vcpu_is_preempted, native_vcpu_is_preempted); >> + >> +static bool para_vcpu_is_preempted(int cpu) >> +{ >> + struct pv_lock_state_region *reg; >> + __le64 preempted_le; >> + >> + reg = per_cpu_ptr(&lock_state_region, cpu); >> + if (!reg->kaddr) { >> + pr_warn_once("PV lock enabled but not configured for cpu %d\n", >> + cpu); >> + return false; >> + } >> + >> + preempted_le = le64_to_cpu(READ_ONCE(reg->kaddr->preempted)); >> + >> + return !!(preempted_le); >> +} >> + >> +static int pvlock_vcpu_state_dying_cpu(unsigned int cpu) >> +{ >> + struct pv_lock_state_region *reg; >> + >> + reg = this_cpu_ptr(&lock_state_region); >> + if (!reg->kaddr) >> + return 0; >> + >> + memunmap(reg->kaddr); >> + memset(reg, 0, sizeof(*reg)); >> + >> + return 0; >> +} >> + >> +static int init_pvlock_vcpu_state(unsigned int cpu) >> +{ >> + struct pv_lock_state_region *reg; >> + struct arm_smccc_res res; >> + >> + reg = this_cpu_ptr(&lock_state_region); >> + >> + arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_LOCK_PREEMPTED, &res); >> + >> + if (res.a0 == SMCCC_RET_NOT_SUPPORTED) { >> + pr_warn("Failed to init PV lock data structure\n"); >> + return -EINVAL; >> + } >> + >> + reg->kaddr = memremap(res.a0, >> + sizeof(struct pvlock_vcpu_state), >> + MEMREMAP_WB); >> + >> + if (!reg->kaddr) { >> + pr_warn("Failed to map PV lock data structure\n"); >> + return -ENOMEM; >> + } >> + >> + return 0; >> +} >> + >> +static int kvm_arm_init_pvlock(void) >> +{ >> + int ret; >> + >> + ret = cpuhp_setup_state(CPUHP_AP_ARM_KVM_PVLOCK_STARTING, >> + "hypervisor/arm/pvlock:starting", >> + init_pvlock_vcpu_state, >> + pvlock_vcpu_state_dying_cpu); >> + if (ret < 0) { >> + pr_warn("PV-lock init failed\n"); >> + return ret; >> + } >> + >> + return 0; >> +} >> + >> +static bool has_kvm_pvlock(void) >> +{ >> + struct arm_smccc_res res; >> + >> + /* To detect the presence of PV lock support we require SMCCC 1.1+ */ >> + if (arm_smccc_1_1_get_conduit() == SMCCC_CONDUIT_NONE) >> + return false; > > This is unnecessary as arm_smccc_1_1_invoke() will return failure if > there's no conduit (or pre-SMCCC 1.1). I suspect this was a copy/paste > from has_pv_steal_clock() which also has the unnecessary check (patch > welcome ;) ). Thanks for the review! I have sent a seperate patch to remove it from pv_steal_clock: https://lore.kernel.org/all/20221104061659.4116508-1-usama.arif@bytedance.com/. I have removed it from pv_lock as well in the v2 patchset: https://lore.kernel.org/all/20221104062105.4119003-1-usama.arif@bytedance.com/. > >> + >> + arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID, >> + ARM_SMCCC_HV_PV_LOCK_FEATURES, &res); > > Since this is a 'OWNER_VENDOR_HYP' call this should really be preceded > by a check that we're running under the expected hypervisor. See e.g. > kvm_init_hyp_services(). > > Of course for KVM we already have a (different) discovery mechanism and > this could be included as a ARM_SMCCC_KVM_FUNC_xxx feature. This > has_kvm_pvlock() function would then simply be: > > static bool has_kvm_pvlock(void) > { > return kvm_arm_hyp_service_available(ARM_SMCC_KVM_FUNC_PVLOCK); > } Thanks, I have simplified has_kvm_pvlock to above. I also changed the code in the v2 revision, so that its just 1 hypercall, ARM_SMCCC_VENDOR_HYP_KVM_PV_LOCK_FUNC_ID. This is similar to how it is done in ptp_kvm vendor call. Usama > > Steve > >> + >> + if (res.a0 != SMCCC_RET_SUCCESS) >> + return false; >> + >> + arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_LOCK_FEATURES, >> + ARM_SMCCC_HV_PV_LOCK_PREEMPTED, &res); >> + >> + return (res.a0 == SMCCC_RET_SUCCESS); >> +} >> + >> +int __init pv_lock_init(void) >> +{ >> + int ret; >> + >> + if (is_hyp_mode_available()) >> + return 0; >> + >> + if (!has_kvm_pvlock()) >> + return 0; >> + >> + ret = kvm_arm_init_pvlock(); >> + if (ret) >> + return ret; >> + >> + static_call_update(pv_vcpu_is_preempted, para_vcpu_is_preempted); >> + pr_info("using PV-lock preempted\n"); >> + >> + return 0; >> +} >> \ No newline at end of file >> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c >> index fea3223704b6..05ca07ac5800 100644 >> --- a/arch/arm64/kernel/setup.c >> +++ b/arch/arm64/kernel/setup.c >> @@ -42,6 +42,7 @@ >> #include >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -360,6 +361,8 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p) >> smp_init_cpus(); >> smp_build_mpidr_hash(); >> >> + pv_lock_init(); >> + >> /* Init percpu seeds for random tags after cpus are set up. */ >> kasan_init_sw_tags(); >> >> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h >> index f61447913db9..c0ee11855c73 100644 >> --- a/include/linux/cpuhotplug.h >> +++ b/include/linux/cpuhotplug.h >> @@ -192,6 +192,7 @@ enum cpuhp_state { >> /* Must be the last timer callback */ >> CPUHP_AP_DUMMY_TIMER_STARTING, >> CPUHP_AP_ARM_XEN_STARTING, >> + CPUHP_AP_ARM_KVM_PVLOCK_STARTING, >> CPUHP_AP_ARM_CORESIGHT_STARTING, >> CPUHP_AP_ARM_CORESIGHT_CTI_STARTING, >> CPUHP_AP_ARM64_ISNDEP_STARTING, >