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kvm: Paravirtual ticketlocks support for linux guests running on KVM hypervisor
During smp_boot_cpus paravirtualied KVM guest detects if the hypervisor has required feature (KVM_FEATURE_PV_UNHALT) to support pv-ticketlocks. If so, support for pv-ticketlocks is registered via pv_lock_ops. Use KVM_HC_KICK_CPU hypercall to wakeup waiting/halted vcpu. Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20130810193849.GA25260@linux.vnet.ibm.com Signed-off-by: Suzuki Poulose <suzuki@in.ibm.com> [Raghu: check_zero race fix, enum for kvm_contention_stat, jumplabel related changes, addition of safe_halt for irq enabled case, bailout spinning in nmi case(Gleb)] Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> Acked-by: Gleb Natapov <gleb@redhat.com> Acked-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Srivatsa Vaddagiri
Ingo Molnar
parent
1e20eb8557
commit
92b75202e5
@ -118,10 +118,20 @@ void kvm_async_pf_task_wait(u32 token);
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void kvm_async_pf_task_wake(u32 token);
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u32 kvm_read_and_reset_pf_reason(void);
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extern void kvm_disable_steal_time(void);
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#else
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#define kvm_guest_init() do { } while (0)
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#ifdef CONFIG_PARAVIRT_SPINLOCKS
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void __init kvm_spinlock_init(void);
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#else /* !CONFIG_PARAVIRT_SPINLOCKS */
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static inline void kvm_spinlock_init(void)
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{
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}
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#endif /* CONFIG_PARAVIRT_SPINLOCKS */
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#else /* CONFIG_KVM_GUEST */
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#define kvm_guest_init() do {} while (0)
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#define kvm_async_pf_task_wait(T) do {} while(0)
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#define kvm_async_pf_task_wake(T) do {} while(0)
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static inline u32 kvm_read_and_reset_pf_reason(void)
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{
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return 0;
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@ -34,6 +34,7 @@
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/kprobes.h>
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#include <linux/debugfs.h>
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#include <asm/timer.h>
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#include <asm/cpu.h>
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#include <asm/traps.h>
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@ -419,6 +420,7 @@ static void __init kvm_smp_prepare_boot_cpu(void)
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WARN_ON(kvm_register_clock("primary cpu clock"));
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kvm_guest_cpu_init();
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native_smp_prepare_boot_cpu();
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kvm_spinlock_init();
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}
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static void kvm_guest_cpu_online(void *dummy)
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@ -523,3 +525,263 @@ static __init int activate_jump_labels(void)
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return 0;
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}
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arch_initcall(activate_jump_labels);
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#ifdef CONFIG_PARAVIRT_SPINLOCKS
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/* Kick a cpu by its apicid. Used to wake up a halted vcpu */
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void kvm_kick_cpu(int cpu)
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{
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int apicid;
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unsigned long flags = 0;
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apicid = per_cpu(x86_cpu_to_apicid, cpu);
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kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
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}
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enum kvm_contention_stat {
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TAKEN_SLOW,
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TAKEN_SLOW_PICKUP,
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RELEASED_SLOW,
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RELEASED_SLOW_KICKED,
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NR_CONTENTION_STATS
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};
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#ifdef CONFIG_KVM_DEBUG_FS
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#define HISTO_BUCKETS 30
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static struct kvm_spinlock_stats
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{
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u32 contention_stats[NR_CONTENTION_STATS];
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u32 histo_spin_blocked[HISTO_BUCKETS+1];
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u64 time_blocked;
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} spinlock_stats;
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static u8 zero_stats;
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static inline void check_zero(void)
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{
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u8 ret;
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u8 old;
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old = ACCESS_ONCE(zero_stats);
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if (unlikely(old)) {
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ret = cmpxchg(&zero_stats, old, 0);
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/* This ensures only one fellow resets the stat */
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if (ret == old)
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memset(&spinlock_stats, 0, sizeof(spinlock_stats));
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}
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}
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static inline void add_stats(enum kvm_contention_stat var, u32 val)
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{
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check_zero();
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spinlock_stats.contention_stats[var] += val;
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}
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static inline u64 spin_time_start(void)
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{
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return sched_clock();
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}
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static void __spin_time_accum(u64 delta, u32 *array)
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{
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unsigned index;
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index = ilog2(delta);
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check_zero();
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if (index < HISTO_BUCKETS)
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array[index]++;
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else
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array[HISTO_BUCKETS]++;
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}
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static inline void spin_time_accum_blocked(u64 start)
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{
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u32 delta;
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delta = sched_clock() - start;
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__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
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spinlock_stats.time_blocked += delta;
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}
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static struct dentry *d_spin_debug;
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static struct dentry *d_kvm_debug;
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struct dentry *kvm_init_debugfs(void)
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{
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d_kvm_debug = debugfs_create_dir("kvm", NULL);
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if (!d_kvm_debug)
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printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n");
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return d_kvm_debug;
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}
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static int __init kvm_spinlock_debugfs(void)
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{
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struct dentry *d_kvm;
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d_kvm = kvm_init_debugfs();
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if (d_kvm == NULL)
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return -ENOMEM;
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d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);
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debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
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debugfs_create_u32("taken_slow", 0444, d_spin_debug,
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&spinlock_stats.contention_stats[TAKEN_SLOW]);
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debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
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&spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
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debugfs_create_u32("released_slow", 0444, d_spin_debug,
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&spinlock_stats.contention_stats[RELEASED_SLOW]);
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debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
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&spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
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debugfs_create_u64("time_blocked", 0444, d_spin_debug,
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&spinlock_stats.time_blocked);
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debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
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spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
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return 0;
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}
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fs_initcall(kvm_spinlock_debugfs);
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#else /* !CONFIG_KVM_DEBUG_FS */
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static inline void add_stats(enum kvm_contention_stat var, u32 val)
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{
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}
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static inline u64 spin_time_start(void)
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{
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return 0;
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}
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static inline void spin_time_accum_blocked(u64 start)
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{
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}
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#endif /* CONFIG_KVM_DEBUG_FS */
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struct kvm_lock_waiting {
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struct arch_spinlock *lock;
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__ticket_t want;
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};
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/* cpus 'waiting' on a spinlock to become available */
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static cpumask_t waiting_cpus;
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/* Track spinlock on which a cpu is waiting */
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static DEFINE_PER_CPU(struct kvm_lock_waiting, klock_waiting);
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static void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
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{
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struct kvm_lock_waiting *w;
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int cpu;
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u64 start;
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unsigned long flags;
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if (in_nmi())
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return;
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w = &__get_cpu_var(klock_waiting);
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cpu = smp_processor_id();
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start = spin_time_start();
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/*
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* Make sure an interrupt handler can't upset things in a
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* partially setup state.
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*/
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local_irq_save(flags);
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/*
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* The ordering protocol on this is that the "lock" pointer
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* may only be set non-NULL if the "want" ticket is correct.
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* If we're updating "want", we must first clear "lock".
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*/
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w->lock = NULL;
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smp_wmb();
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w->want = want;
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smp_wmb();
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w->lock = lock;
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add_stats(TAKEN_SLOW, 1);
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/*
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* This uses set_bit, which is atomic but we should not rely on its
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* reordering gurantees. So barrier is needed after this call.
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*/
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cpumask_set_cpu(cpu, &waiting_cpus);
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barrier();
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/*
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* Mark entry to slowpath before doing the pickup test to make
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* sure we don't deadlock with an unlocker.
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*/
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__ticket_enter_slowpath(lock);
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/*
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* check again make sure it didn't become free while
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* we weren't looking.
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*/
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if (ACCESS_ONCE(lock->tickets.head) == want) {
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add_stats(TAKEN_SLOW_PICKUP, 1);
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goto out;
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}
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/*
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* halt until it's our turn and kicked. Note that we do safe halt
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* for irq enabled case to avoid hang when lock info is overwritten
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* in irq spinlock slowpath and no spurious interrupt occur to save us.
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*/
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if (arch_irqs_disabled_flags(flags))
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halt();
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else
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safe_halt();
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out:
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cpumask_clear_cpu(cpu, &waiting_cpus);
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w->lock = NULL;
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local_irq_restore(flags);
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spin_time_accum_blocked(start);
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}
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PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
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/* Kick vcpu waiting on @lock->head to reach value @ticket */
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static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
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{
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int cpu;
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add_stats(RELEASED_SLOW, 1);
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for_each_cpu(cpu, &waiting_cpus) {
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const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
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if (ACCESS_ONCE(w->lock) == lock &&
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ACCESS_ONCE(w->want) == ticket) {
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add_stats(RELEASED_SLOW_KICKED, 1);
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kvm_kick_cpu(cpu);
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break;
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}
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}
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}
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/*
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* Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
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*/
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void __init kvm_spinlock_init(void)
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{
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if (!kvm_para_available())
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return;
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/* Does host kernel support KVM_FEATURE_PV_UNHALT? */
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if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
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return;
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printk(KERN_INFO "KVM setup paravirtual spinlock\n");
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static_key_slow_inc(¶virt_ticketlocks_enabled);
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pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
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pv_lock_ops.unlock_kick = kvm_unlock_kick;
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}
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#endif /* CONFIG_PARAVIRT_SPINLOCKS */
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