[PATCH 10/15] KVM: MMU: lockless walking shadow page table

Xiao Guangrong
2011-06-07T13:02:30Z

Using rcu to protect shadow pages table to be freed, so we can safely walk it,
it should run fast and is needed by mmio page fault

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
arch/x86/include/asm/kvm_host.h | 4 ++
arch/x86/kvm/mmu.c | 79 ++++++++++++++++++++++++++++++---------
arch/x86/kvm/mmu.h | 4 +-
arch/x86/kvm/vmx.c | 2 +-
4 files changed, 69 insertions(+), 20 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 326af42..260582b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -232,6 +232,8 @@ struct kvm_mmu_page {
unsigned int unsync_children;
unsigned long parent_ptes; /* Reverse mapping for parent_pte */
DECLARE_BITMAP(unsync_child_bitmap, 512);
+
+ struct rcu_head rcu;
};

struct kvm_pv_mmu_op_buffer {
@@ -478,6 +480,8 @@ 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 9f3a746..52d4682 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1675,6 +1675,30 @@ static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
return ret;
}

+static void free_mmu_pages_unlock_parts(struct list_head *invalid_list)
+{
+ struct kvm_mmu_page *sp;
+
+ list_for_each_entry(sp, invalid_list, link)
+ kvm_mmu_free_lock_parts(sp);
+}
+
+static void free_invalid_pages_rcu(struct rcu_head *head)
+{
+ struct kvm_mmu_page *next, *sp;
+
+ sp = container_of(head, struct kvm_mmu_page, rcu);
+ while (sp) {
+ if (!list_empty(&sp->link))
+ next = list_first_entry(&sp->link,
+ struct kvm_mmu_page, link);
+ else
+ next = NULL;
+ kvm_mmu_free_unlock_parts(sp);
+ sp = next;
+ }
+}
+
static void kvm_mmu_commit_zap_page(struct kvm *kvm,
struct list_head *invalid_list)
{
@@ -1685,6 +1709,14 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,

kvm_flush_remote_tlbs(kvm);

+ if (atomic_read(&kvm->arch.reader_counter)) {
+ free_mmu_pages_unlock_parts(invalid_list);
+ sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
+ list_del_init(invalid_list);
+ call_rcu(&sp->rcu, free_invalid_pages_rcu);
+ return;
+ }
+
do {
sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
WARN_ON(!sp->role.invalid || sp->root_count);
@@ -2601,6 +2633,35 @@ static gpa_t nonpaging_gva_to_gpa_nested(struct kvm_vcpu *vcpu, gva_t vaddr,
return vcpu->arch.nested_mmu.translate_gpa(vcpu, vaddr, access);
}

+int kvm_mmu_walk_shadow_page_lockless(struct kvm_vcpu *vcpu, u64 addr,
+ u64 sptes[4])
+{
+ struct kvm_shadow_walk_iterator iterator;
+ int nr_sptes = 0;
+
+ rcu_read_lock();
+
+ atomic_inc(&vcpu->kvm->arch.reader_counter);
+ /* Increase the counter before walking shadow page table */
+ smp_mb__after_atomic_inc();
+
+ for_each_shadow_entry(vcpu, addr, iterator) {
+ sptes[iterator.level-1] = *iterator.sptep;
+ nr_sptes++;
+ if (!is_shadow_present_pte(*iterator.sptep))
+ break;
+ }
+
+ /* Decrease the counter after walking shadow page table finished */
+ smp_mb__before_atomic_dec();
+ atomic_dec(&vcpu->kvm->arch.reader_counter);
+
+ rcu_read_unlock();
+
+ return nr_sptes;
+}
+EXPORT_SYMBOL_GPL(kvm_mmu_walk_shadow_page_lockless);
+
static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
u32 error_code, bool prefault)
{
@@ -3684,24 +3745,6 @@ out:
return r;
}

-int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4])
-{
- struct kvm_shadow_walk_iterator iterator;
- int nr_sptes = 0;
-
- spin_lock(&vcpu->kvm->mmu_lock);
- for_each_shadow_entry(vcpu, addr, iterator) {
- sptes[iterator.level-1] = *iterator.sptep;
- nr_sptes++;
- if (!is_shadow_present_pte(*iterator.sptep))
- break;
- }
- spin_unlock(&vcpu->kvm->mmu_lock);
-
- return nr_sptes;
-}
-EXPORT_SYMBOL_GPL(kvm_mmu_get_spte_hierarchy);
-
void kvm_mmu_destroy(struct kvm_vcpu *vcpu)
{
ASSERT(vcpu);
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 05310b1..e7725c4 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -48,7 +48,9 @@
#define PFERR_RSVD_MASK (1U << 3)
#define PFERR_FETCH_MASK (1U << 4)

-int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4]);
+int kvm_mmu_walk_shadow_page_lockless(struct kvm_vcpu *vcpu, u64 addr,
+ u64 sptes[4]);
+
int kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context);

static inline unsigned int kvm_mmu_available_pages(struct kvm *kvm)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b54c186..20dbf7f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4681,7 +4681,7 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
printk(KERN_ERR "EPT: Misconfiguration.\n");
printk(KERN_ERR "EPT: GPA: 0x%llx\n", gpa);

- nr_sptes = kvm_mmu_get_spte_hierarchy(vcpu, gpa, sptes);
+ nr_sptes = kvm_mmu_walk_shadow_page_lockless(vcpu, gpa, sptes);

for (i = PT64_ROOT_LEVEL; i > PT64_ROOT_LEVEL - nr_sptes; --i)
ept_misconfig_inspect_spte(vcpu, sptes[i-1], i);
--
1.7.4.4