[PATCH 2/2] KVM: Convert read-only users of vm_list to RCU

Jan Kiszka
2011-02-08T11:55:52Z

Only for walking the list of VMs, we do not need to hold the preemption
disabling kvm_lock. Convert stat services, the cpufreq callback and
mmu_shrink to RCU. For the latter, special care is required to
synchronize its list_move_tail with kvm_destroy_vm.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
arch/x86/kvm/mmu.c | 14 +++++++++-----
arch/x86/kvm/x86.c | 4 ++--
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 17 ++++++++++-------
4 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index b6a9963..e9d0ed8 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3587,9 +3587,9 @@ static int mmu_shrink(struct shrinker *shrink, int nr_to_scan, gfp_t gfp_mask)
if (nr_to_scan == 0)
goto out;

- raw_spin_lock(&kvm_lock);
+ rcu_read_lock();

- list_for_each_entry(kvm, &vm_list, vm_list) {
+ list_for_each_entry_rcu(kvm, &vm_list, vm_list) {
int idx, freed_pages;
LIST_HEAD(invalid_list);

@@ -3607,10 +3607,14 @@ static int mmu_shrink(struct shrinker *shrink, int nr_to_scan, gfp_t gfp_mask)
spin_unlock(&kvm->mmu_lock);
srcu_read_unlock(&kvm->srcu, idx);
}
- if (kvm_freed)
- list_move_tail(&kvm_freed->vm_list, &vm_list);
+ if (kvm_freed) {
+ raw_spin_lock(&kvm_lock);
+ if (!kvm->deleted)
+ list_move_tail(&kvm_freed->vm_list, &vm_list);
+ raw_spin_unlock(&kvm_lock);
+ }

- raw_spin_unlock(&kvm_lock);
+ rcu_read_unlock();

out:
return percpu_counter_read_positive(&kvm_total_used_mmu_pages);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ae6e75b..01fa1ea 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4578,7 +4578,7 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va

smp_call_function_single(freq->cpu, tsc_khz_changed, freq, 1);

- raw_spin_lock(&kvm_lock);
+ rcu_read_lock();
list_for_each_entry(kvm, &vm_list, vm_list) {
kvm_for_each_vcpu(i, vcpu, kvm) {
if (vcpu->cpu != freq->cpu)
@@ -4588,7 +4588,7 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va
send_ipi = 1;
}
}
- raw_spin_unlock(&kvm_lock);
+ rcu_read_unlock();

if (freq->old < freq->new && send_ipi) {
/*
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c8dee22..9074cac 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -234,6 +234,7 @@ struct kvm {
#endif
struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
atomic_t online_vcpus;
+ bool deleted;
struct list_head vm_list;
struct mutex lock;
struct kvm_io_bus *buses[KVM_NR_BUSES];
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7b70c67..b5a05b5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -546,9 +546,13 @@ static void kvm_destroy_vm(struct kvm *kvm)
struct mm_struct *mm = kvm->mm;

kvm_arch_sync_events(kvm);
+
raw_spin_lock(&kvm_lock);
list_del(&kvm->vm_list);
+ kvm->deleted = true;
raw_spin_unlock(&kvm_lock);
+ synchronize_rcu();
+
kvm_free_irq_routing(kvm);
for (i = 0; i < KVM_NR_BUSES; i++)
kvm_io_bus_destroy(kvm->buses[i]);
@@ -2347,10 +2351,10 @@ static int vm_stat_get(void *_offset, u64 *val)
struct kvm *kvm;

*val = 0;
- raw_spin_lock(&kvm_lock);
- list_for_each_entry(kvm, &vm_list, vm_list)
+ rcu_read_lock();
+ list_for_each_entry_rcu(kvm, &vm_list, vm_list)
*val += *(u32 *)((void *)kvm + offset);
- raw_spin_unlock(&kvm_lock);
+ rcu_read_unlock();
return 0;
}

@@ -2364,12 +2368,11 @@ static int vcpu_stat_get(void *_offset, u64 *val)
int i;

*val = 0;
- raw_spin_lock(&kvm_lock);
- list_for_each_entry(kvm, &vm_list, vm_list)
+ rcu_read_lock();
+ list_for_each_entry_rcu(kvm, &vm_list, vm_list)
kvm_for_each_vcpu(i, vcpu, kvm)
*val += *(u32 *)((void *)vcpu + offset);
-
- raw_spin_unlock(&kvm_lock);
+ rcu_read_unlock();
return 0;
}

--
1.7.1