The non-RCU path costs us two atomic operations, as well as extra
code complexity.
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 2 --
arch/x86/kvm/mmu.c | 46 ++++++++-------------------------------
2 files changed, 9 insertions(+), 39 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f624ca7..b885445 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -536,8 +536,6 @@ struct kvm_arch {
u64 hv_guest_os_id;
u64 hv_hypercall;
- atomic_t reader_counter;
-
#ifdef CONFIG_KVM_MMU_AUDIT
int audit_point;
#endif
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 29ad6f9..c10f60b 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -549,23 +549,6 @@ static u64 mmu_spte_get_lockless(u64 *sptep)
return __get_spte_lockless(sptep);
}
-static void walk_shadow_page_lockless_begin(struct kvm_vcpu *vcpu)
-{
- rcu_read_lock();
- atomic_inc(&vcpu->kvm->arch.reader_counter);
-
- /* Increase the counter before walking shadow page table */
- smp_mb__after_atomic_inc();
-}
-
-static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu)
-{
- /* Decrease the counter after walking shadow page table finished */
- smp_mb__before_atomic_dec();
- atomic_dec(&vcpu->kvm->arch.reader_counter);
- rcu_read_unlock();
-}
-
static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
struct kmem_cache *base_cache, int min)
{
@@ -2023,23 +2006,12 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
kvm_flush_remote_tlbs(kvm);
- if (atomic_read(&kvm->arch.reader_counter)) {
- kvm_mmu_isolate_pages(invalid_list);
- sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
- list_del_init(invalid_list);
-
- trace_kvm_mmu_delay_free_pages(sp);
- call_rcu(&sp->rcu, free_pages_rcu);
- return;
- }
-
- do {
- sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
- WARN_ON(!sp->role.invalid || sp->root_count);
- kvm_mmu_isolate_page(sp);
- kvm_mmu_free_page(sp);
- } while (!list_empty(invalid_list));
+ kvm_mmu_isolate_pages(invalid_list);
+ sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
+ list_del_init(invalid_list);
+ trace_kvm_mmu_delay_free_pages(sp);
+ call_rcu(&sp->rcu, free_pages_rcu);
}
/*
@@ -2976,11 +2948,11 @@ static u64 walk_shadow_page_get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr)
struct kvm_shadow_walk_iterator iterator;
u64 spte = 0ull;
- walk_shadow_page_lockless_begin(vcpu);
+ rcu_read_lock();
for_each_shadow_entry_lockless(vcpu, addr, iterator, spte)
if (!is_shadow_present_pte(spte))
break;
- walk_shadow_page_lockless_end(vcpu);
+ rcu_read_unlock();
return spte;
}
@@ -4060,14 +4032,14 @@ int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4])
u64 spte;
int nr_sptes = 0;
- walk_shadow_page_lockless_begin(vcpu);
+ rcu_read_lock();
for_each_shadow_entry_lockless(vcpu, addr, iterator, spte) {
sptes[iterator.level-1] = spte;
nr_sptes++;
if (!is_shadow_present_pte(spte))
break;
}
- walk_shadow_page_lockless_end(vcpu);
+ rcu_read_unlock();
return nr_sptes;
}
--
1.7.10
--
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