PV-vcpu-state is a per-CPU struct, which, for the time being,
holds boolean `preempted' vCPU state. During the startup,
given that host supports PV-state, each guest vCPU sends
a pointer to its per-CPU variable to the host as a payload
with the SMCCC HV call, so that host can update vCPU state
when it puts or loads vCPU.
This has impact on the guest's scheduler:
[..]
wake_up_process()
try_to_wake_up()
select_task_rq_fair()
available_idle_cpu()
vcpu_is_preempted()
Some sched benchmarks data is available on the github page [0].
[0] https://github.com/sergey-senozhatsky/arm64-vcpu_is_preempted
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
arch/arm64/include/asm/paravirt.h | 19 +++++++
arch/arm64/kernel/paravirt.c | 94 +++++++++++++++++++++++++++++++
arch/arm64/kernel/smp.c | 4 ++
3 files changed, 117 insertions(+)
diff --git a/arch/arm64/include/asm/paravirt.h b/arch/arm64/include/asm/paravirt.h
index 9aa193e0e8f2..a3f7665dff38 100644
--- a/arch/arm64/include/asm/paravirt.h
+++ b/arch/arm64/include/asm/paravirt.h
@@ -2,6 +2,11 @@
#ifndef _ASM_ARM64_PARAVIRT_H
#define _ASM_ARM64_PARAVIRT_H
+struct vcpu_state {
+ bool preempted;
+ u8 reserved[63];
+};
+
#ifdef CONFIG_PARAVIRT
#include <linux/static_call_types.h>
@@ -20,8 +25,22 @@ static inline u64 paravirt_steal_clock(int cpu)
int __init pv_time_init(void);
+bool dummy_vcpu_is_preempted(unsigned int cpu);
+
+extern struct static_key pv_vcpu_is_preempted_enabled;
+DECLARE_STATIC_CALL(pv_vcpu_is_preempted, dummy_vcpu_is_preempted);
+
+static inline bool paravirt_vcpu_is_preempted(unsigned int cpu)
+{
+ return static_call(pv_vcpu_is_preempted)(cpu);
+}
+
+int __init pv_vcpu_state_init(void);
+
#else
+#define pv_vcpu_state_init() do {} while (0)
+
#define pv_time_init() do {} while (0)
#endif // CONFIG_PARAVIRT
diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c
index 75fed4460407..d8fc46795d94 100644
--- a/arch/arm64/kernel/paravirt.c
+++ b/arch/arm64/kernel/paravirt.c
@@ -40,6 +40,11 @@ struct pv_time_stolen_time_region {
static DEFINE_PER_CPU(struct pv_time_stolen_time_region, stolen_time_region);
+static DEFINE_PER_CPU(struct vcpu_state, vcpus_states);
+struct static_key pv_vcpu_is_preempted_enabled;
+
+DEFINE_STATIC_CALL(pv_vcpu_is_preempted, dummy_vcpu_is_preempted);
+
static bool steal_acc = true;
static int __init parse_no_stealacc(char *arg)
{
@@ -165,3 +170,92 @@ int __init pv_time_init(void)
return 0;
}
+
+bool dummy_vcpu_is_preempted(unsigned int cpu)
+{
+ return false;
+}
+
+static bool __vcpu_is_preempted(unsigned int cpu)
+{
+ struct vcpu_state *st;
+
+ st = &per_cpu(vcpus_states, cpu);
+ return READ_ONCE(st->preempted);
+}
+
+static bool has_pv_vcpu_state(void)
+{
+ struct arm_smccc_res res;
+
+ /* To detect the presence of PV time support we require SMCCC 1.1+ */
+ if (arm_smccc_1_1_get_conduit() == SMCCC_CONDUIT_NONE)
+ return false;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
+ ARM_SMCCC_HV_PV_VCPU_STATE_FEATURES,
+ &res);
+
+ if (res.a0 != SMCCC_RET_SUCCESS)
+ return false;
+ return true;
+}
+
+static int __pv_vcpu_state_hook(unsigned int cpu, int event)
+{
+ struct arm_smccc_res res;
+ struct vcpu_state *st;
+
+ st = &per_cpu(vcpus_states, cpu);
+ arm_smccc_1_1_invoke(event, virt_to_phys(st), &res);
+ if (res.a0 != SMCCC_RET_SUCCESS)
+ return -EINVAL;
+ return 0;
+}
+
+static int vcpu_state_init(unsigned int cpu)
+{
+ int ret = __pv_vcpu_state_hook(cpu, ARM_SMCCC_HV_PV_VCPU_STATE_INIT);
+
+ if (ret)
+ pr_warn("Unable to ARM_SMCCC_HV_PV_STATE_INIT\n");
+ return ret;
+}
+
+static int vcpu_state_release(unsigned int cpu)
+{
+ int ret = __pv_vcpu_state_hook(cpu, ARM_SMCCC_HV_PV_VCPU_STATE_RELEASE);
+
+ if (ret)
+ pr_warn("Unable to ARM_SMCCC_HV_PV_STATE_RELEASE\n");
+ return ret;
+}
+
+static int pv_vcpu_state_register_hooks(void)
+{
+ int ret;
+
+ ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
+ "hypervisor/arm/pvstate:starting",
+ vcpu_state_init,
+ vcpu_state_release);
+ if (ret < 0)
+ pr_warn("Failed to register CPU hooks\n");
+ return 0;
+}
+
+int __init pv_vcpu_state_init(void)
+{
+ int ret;
+
+ if (!has_pv_vcpu_state())
+ return 0;
+
+ ret = pv_vcpu_state_register_hooks();
+ if (ret)
+ return ret;
+
+ static_call_update(pv_vcpu_is_preempted, __vcpu_is_preempted);
+ static_key_slow_inc(&pv_vcpu_is_preempted_enabled);
+ return 0;
+}
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 6f6ff072acbd..20d42e0f2a99 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -50,6 +50,7 @@
#include <asm/tlbflush.h>
#include <asm/ptrace.h>
#include <asm/virt.h>
+#include <asm/paravirt.h>
#define CREATE_TRACE_POINTS
#include <trace/events/ipi.h>
@@ -756,6 +757,9 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
numa_store_cpu_info(this_cpu);
numa_add_cpu(this_cpu);
+ /* Init paravirt CPU state */
+ pv_vcpu_state_init();
+
/*
* If UP is mandated by "nosmp" (which implies "maxcpus=0"), don't set
* secondary CPUs present.
--
2.32.0.93.g670b81a890-goog
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