[PATCH v2 24/28] KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock
From: Ben Gardon
Date: Tue Feb 02 2021 - 14:06:00 EST
To reduce lock contention and interference with page fault handlers,
allow the TDP MMU function to zap a GFN range to operate under the MMU
read lock.
Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 13 ++-
arch/x86/kvm/mmu/mmu_internal.h | 6 +-
arch/x86/kvm/mmu/tdp_mmu.c | 165 +++++++++++++++++++++++++-------
arch/x86/kvm/mmu/tdp_mmu.h | 3 +-
4 files changed, 145 insertions(+), 42 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3d181a2b2485..254ff87d2a61 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5518,13 +5518,17 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
}
}
+ kvm_mmu_unlock(kvm);
+
if (kvm->arch.tdp_mmu_enabled) {
- flush = kvm_tdp_mmu_zap_gfn_range(kvm, gfn_start, gfn_end);
+ read_lock(&kvm->mmu_lock);
+ flush = kvm_tdp_mmu_zap_gfn_range(kvm, gfn_start, gfn_end,
+ true);
if (flush)
kvm_flush_remote_tlbs(kvm);
- }
- write_unlock(&kvm->mmu_lock);
+ read_unlock(&kvm->mmu_lock);
+ }
}
static bool slot_rmap_write_protect(struct kvm *kvm,
@@ -6015,7 +6019,8 @@ static void kvm_recover_nx_lpages(struct kvm *kvm)
WARN_ON_ONCE(!sp->lpage_disallowed);
if (sp->tdp_mmu_page) {
kvm_tdp_mmu_zap_gfn_range(kvm, sp->gfn,
- sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level));
+ sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level),
+ false);
} else {
kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
WARN_ON_ONCE(sp->lpage_disallowed);
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 7f599cc64178..7df209fb8051 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -40,7 +40,11 @@ struct kvm_mmu_page {
u64 *spt;
/* hold the gfn of each spte inside spt */
gfn_t *gfns;
- int root_count; /* Currently serving as active root */
+ /* Currently serving as active root */
+ union {
+ int root_count;
+ refcount_t tdp_mmu_root_count;
+ };
unsigned int unsync_children;
struct kvm_rmap_head parent_ptes; /* rmap pointers to parent sptes */
DECLARE_BITMAP(unsync_child_bitmap, 512);
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 0dd27e000dd0..de26762433ea 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -52,46 +52,104 @@ void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm)
rcu_barrier();
}
-static void tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
+static __always_inline __must_check bool tdp_mmu_get_root(struct kvm *kvm,
+ struct kvm_mmu_page *root)
{
- if (kvm_mmu_put_root(kvm, root))
- kvm_tdp_mmu_free_root(kvm, root);
+ return refcount_inc_not_zero(&root->tdp_mmu_root_count);
}
-static inline bool tdp_mmu_next_root_valid(struct kvm *kvm,
- struct kvm_mmu_page *root)
+static __always_inline void tdp_mmu_put_root(struct kvm *kvm,
+ struct kvm_mmu_page *root,
+ bool shared)
{
- lockdep_assert_held_write(&kvm->mmu_lock);
+ int root_count;
+ int r;
- if (list_entry_is_head(root, &kvm->arch.tdp_mmu_roots, link))
- return false;
+ if (shared) {
+ lockdep_assert_held_read(&kvm->mmu_lock);
- kvm_mmu_get_root(kvm, root);
- return true;
+ root_count = atomic_read(&root->tdp_mmu_root_count.refs);
+
+ /*
+ * If this is not the last reference on the root, it can be
+ * dropped under the MMU read lock.
+ */
+ if (root_count > 1) {
+ r = atomic_cmpxchg(&root->tdp_mmu_root_count.refs,
+ root_count, root_count - 1);
+ if (r == root_count)
+ return;
+ }
+
+ /*
+ * If the cmpxchg failed because of a race or this is the
+ * last reference on the root, drop the read lock, and
+ * reacquire the MMU lock in write mode.
+ */
+ read_unlock(&kvm->mmu_lock);
+ write_lock(&kvm->mmu_lock);
+ } else {
+ lockdep_assert_held_write(&kvm->mmu_lock);
+ }
+
+ /*
+ * No other thread can modify the root count since this thread holds
+ * the MMU lock in write mode.
+ */
+ BUG_ON(!atomic_read(&root->tdp_mmu_root_count.refs));
+
+ if (refcount_dec_and_test(&root->tdp_mmu_root_count))
+ kvm_tdp_mmu_free_root(kvm, root);
+
+ if (shared) {
+ write_unlock(&kvm->mmu_lock);
+ read_lock(&kvm->mmu_lock);
+
+ }
}
static inline struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
- struct kvm_mmu_page *root)
+ struct kvm_mmu_page *root,
+ bool shared)
{
struct kvm_mmu_page *next_root;
next_root = list_next_entry(root, link);
- tdp_mmu_put_root(kvm, root);
+ tdp_mmu_put_root(kvm, root, shared);
return next_root;
}
+static inline bool tdp_mmu_next_root_valid(struct kvm *kvm,
+ struct kvm_mmu_page *root)
+{
+ for (;;) {
+ if (list_entry_is_head(root, &kvm->arch.tdp_mmu_roots, link))
+ return false;
+
+ if (tdp_mmu_get_root(kvm, root))
+ return true;
+
+ root = list_next_entry(root, link);
+ }
+
+}
+
/*
* Note: this iterator gets and puts references to the roots it iterates over.
* This makes it safe to release the MMU lock and yield within the loop, but
* if exiting the loop early, the caller must drop the reference to the most
* recent root. (Unless keeping a live reference is desirable.)
+ *
+ * If shared is set, this function is operating under the MMU lock in read
+ * mode. In the unlikely event that this thread must free a root, the lock
+ * will be temporarily dropped and reacquired in write mode.
*/
-#define for_each_tdp_mmu_root_yield_safe(_kvm, _root) \
+#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _shared) \
for (_root = list_first_entry(&_kvm->arch.tdp_mmu_roots, \
typeof(*_root), link); \
tdp_mmu_next_root_valid(_kvm, _root); \
- _root = tdp_mmu_next_root(_kvm, _root))
+ _root = tdp_mmu_next_root(_kvm, _root, _shared))
#define for_each_tdp_mmu_root(_kvm, _root) \
list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link)
@@ -113,7 +171,7 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
}
static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
- gfn_t start, gfn_t end, bool can_yield);
+ gfn_t start, gfn_t end, bool can_yield, bool shared);
void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
{
@@ -126,7 +184,7 @@ void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
list_del(&root->link);
- zap_gfn_range(kvm, root, 0, max_gfn, false);
+ zap_gfn_range(kvm, root, 0, max_gfn, false, false);
free_page((unsigned long)root->spt);
kmem_cache_free(mmu_page_header_cache, root);
@@ -658,7 +716,8 @@ static inline void tdp_mmu_set_spte_no_dirty_log(struct kvm *kvm,
* Return false if a yield was not needed.
*/
static inline bool tdp_mmu_iter_cond_resched(struct kvm *kvm,
- struct tdp_iter *iter, bool flush)
+ struct tdp_iter *iter, bool flush,
+ bool shared)
{
/* Ensure forward progress has been made before yielding. */
if (iter->next_last_level_gfn == iter->yielded_gfn)
@@ -670,7 +729,11 @@ static inline bool tdp_mmu_iter_cond_resched(struct kvm *kvm,
if (flush)
kvm_flush_remote_tlbs(kvm);
- cond_resched_rwlock_write(&kvm->mmu_lock);
+ if (shared)
+ cond_resched_rwlock_read(&kvm->mmu_lock);
+ else
+ cond_resched_rwlock_write(&kvm->mmu_lock);
+
rcu_read_lock();
WARN_ON(iter->gfn > iter->next_last_level_gfn);
@@ -690,23 +753,38 @@ static inline bool tdp_mmu_iter_cond_resched(struct kvm *kvm,
* non-root pages mapping GFNs strictly within that range. Returns true if
* SPTEs have been cleared and a TLB flush is needed before releasing the
* MMU lock.
+ *
* If can_yield is true, will release the MMU lock and reschedule if the
* scheduler needs the CPU or there is contention on the MMU lock. If this
* function cannot yield, it will not release the MMU lock or reschedule and
* the caller must ensure it does not supply too large a GFN range, or the
* operation can cause a soft lockup.
+ *
+ * If shared is true, this thread holds the MMU lock in read mode and must
+ * account for the possibility that other threads are modifying the paging
+ * structures concurrently. If shared is false, this thread should hold the
+ * MMU in write mode.
*/
static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
- gfn_t start, gfn_t end, bool can_yield)
+ gfn_t start, gfn_t end, bool can_yield, bool shared)
{
struct tdp_iter iter;
bool flush_needed = false;
+#ifdef CONFIG_LOCKDEP
+ if (shared)
+ lockdep_assert_held_read(&kvm->mmu_lock);
+ else
+ lockdep_assert_held_write(&kvm->mmu_lock);
+#endif /* CONFIG_LOCKDEP */
+
rcu_read_lock();
tdp_root_for_each_pte(iter, root, start, end) {
+retry:
if (can_yield &&
- tdp_mmu_iter_cond_resched(kvm, &iter, flush_needed)) {
+ tdp_mmu_iter_cond_resched(kvm, &iter, flush_needed,
+ shared)) {
flush_needed = false;
continue;
}
@@ -724,8 +802,17 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
!is_last_spte(iter.old_spte, iter.level))
continue;
- tdp_mmu_set_spte(kvm, &iter, 0);
- flush_needed = true;
+ if (!shared) {
+ tdp_mmu_set_spte(kvm, &iter, 0);
+ flush_needed = true;
+ } else if (!tdp_mmu_zap_spte_atomic(kvm, &iter)) {
+ /*
+ * The iter must explicitly re-read the SPTE because
+ * the atomic cmpxchg failed.
+ */
+ iter.old_spte = READ_ONCE(*rcu_dereference(iter.sptep));
+ goto retry;
+ }
}
rcu_read_unlock();
@@ -737,14 +824,20 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
* non-root pages mapping GFNs strictly within that range. Returns true if
* SPTEs have been cleared and a TLB flush is needed before releasing the
* MMU lock.
+ *
+ * If shared is true, this thread holds the MMU lock in read mode and must
+ * account for the possibility that other threads are modifying the paging
+ * structures concurrently. If shared is false, this thread should hold the
+ * MMU in write mode.
*/
-bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end)
+bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end,
+ bool shared)
{
struct kvm_mmu_page *root;
bool flush = false;
- for_each_tdp_mmu_root_yield_safe(kvm, root)
- flush |= zap_gfn_range(kvm, root, start, end, true);
+ for_each_tdp_mmu_root_yield_safe(kvm, root, shared)
+ flush |= zap_gfn_range(kvm, root, start, end, true, shared);
return flush;
}
@@ -754,7 +847,7 @@ void kvm_tdp_mmu_zap_all(struct kvm *kvm)
gfn_t max_gfn = 1ULL << (shadow_phys_bits - PAGE_SHIFT);
bool flush;
- flush = kvm_tdp_mmu_zap_gfn_range(kvm, 0, max_gfn);
+ flush = kvm_tdp_mmu_zap_gfn_range(kvm, 0, max_gfn, false);
if (flush)
kvm_flush_remote_tlbs(kvm);
}
@@ -918,7 +1011,7 @@ static int kvm_tdp_mmu_handle_hva_range(struct kvm *kvm, unsigned long start,
int ret = 0;
int as_id;
- for_each_tdp_mmu_root_yield_safe(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root, false) {
as_id = kvm_mmu_page_as_id(root);
slots = __kvm_memslots(kvm, as_id);
kvm_for_each_memslot(memslot, slots) {
@@ -950,7 +1043,7 @@ static int zap_gfn_range_hva_wrapper(struct kvm *kvm,
struct kvm_mmu_page *root, gfn_t start,
gfn_t end, unsigned long unused)
{
- return zap_gfn_range(kvm, root, start, end, false);
+ return zap_gfn_range(kvm, root, start, end, false, false);
}
int kvm_tdp_mmu_zap_hva_range(struct kvm *kvm, unsigned long start,
@@ -1113,7 +1206,7 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
for_each_tdp_pte_min_level(iter, root->spt, root->role.level,
min_level, start, end) {
- if (tdp_mmu_iter_cond_resched(kvm, &iter, false))
+ if (tdp_mmu_iter_cond_resched(kvm, &iter, false, false))
continue;
if (!is_shadow_present_pte(iter.old_spte) ||
@@ -1143,7 +1236,7 @@ bool kvm_tdp_mmu_wrprot_slot(struct kvm *kvm, struct kvm_memory_slot *slot,
int root_as_id;
bool spte_set = false;
- for_each_tdp_mmu_root_yield_safe(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root, false) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;
@@ -1172,7 +1265,7 @@ static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
rcu_read_lock();
tdp_root_for_each_leaf_pte(iter, root, start, end) {
- if (tdp_mmu_iter_cond_resched(kvm, &iter, false))
+ if (tdp_mmu_iter_cond_resched(kvm, &iter, false, false))
continue;
if (spte_ad_need_write_protect(iter.old_spte)) {
@@ -1208,7 +1301,7 @@ bool kvm_tdp_mmu_clear_dirty_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
int root_as_id;
bool spte_set = false;
- for_each_tdp_mmu_root_yield_safe(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root, false) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;
@@ -1304,7 +1397,7 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
rcu_read_lock();
tdp_root_for_each_pte(iter, root, start, end) {
- if (tdp_mmu_iter_cond_resched(kvm, &iter, false))
+ if (tdp_mmu_iter_cond_resched(kvm, &iter, false, false))
continue;
if (!is_shadow_present_pte(iter.old_spte) ||
@@ -1332,7 +1425,7 @@ bool kvm_tdp_mmu_slot_set_dirty(struct kvm *kvm, struct kvm_memory_slot *slot)
int root_as_id;
bool spte_set = false;
- for_each_tdp_mmu_root_yield_safe(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root, false) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;
@@ -1358,7 +1451,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
rcu_read_lock();
tdp_root_for_each_pte(iter, root, start, end) {
- if (tdp_mmu_iter_cond_resched(kvm, &iter, spte_set)) {
+ if (tdp_mmu_iter_cond_resched(kvm, &iter, false, false)) {
spte_set = false;
continue;
}
@@ -1392,7 +1485,7 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
struct kvm_mmu_page *root;
int root_as_id;
- for_each_tdp_mmu_root_yield_safe(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root, false) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index cbbdbadd1526..10ada884270b 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -12,7 +12,8 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t root);
hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root);
-bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end);
+bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end,
+ bool shared);
void kvm_tdp_mmu_zap_all(struct kvm *kvm);
int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
--
2.30.0.365.g02bc693789-goog