[PATCH 10/13] KVM: x86/mmu: Allow zapping collapsible SPTEs to use MMU read lock

From: Ben Gardon
Date: Wed Mar 31 2021 - 17:10:31 EST


To speed the process of disabling dirty logging, change the TDP MMU
function which zaps collapsible SPTEs to run under the MMU read lock.

Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 9 ++++++---
arch/x86/kvm/mmu/tdp_mmu.c | 17 +++++++++++++----
2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index dcbfc784cf2f..81967b4e7d76 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5610,10 +5610,13 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,

write_lock(&kvm->mmu_lock);
slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
-
- if (is_tdp_mmu_enabled(kvm))
- kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot);
write_unlock(&kvm->mmu_lock);
+
+ if (is_tdp_mmu_enabled(kvm)) {
+ read_lock(&kvm->mmu_lock);
+ kvm_tdp_mmu_zap_collapsible_sptes(kvm, memslot);
+ read_unlock(&kvm->mmu_lock);
+ }
}

void kvm_arch_flush_remote_tlbs_memslot(struct kvm *kvm,
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 0e99e4675dd4..862acb868abd 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1335,7 +1335,8 @@ 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, false)) {
+retry:
+ if (tdp_mmu_iter_cond_resched(kvm, &iter, spte_set, true)) {
spte_set = false;
continue;
}
@@ -1350,8 +1351,14 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
pfn, PG_LEVEL_NUM))
continue;

- tdp_mmu_set_spte(kvm, &iter, 0);
-
+ 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;
+ }
spte_set = true;
}

@@ -1370,7 +1377,9 @@ 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, false) {
+ lockdep_assert_held_read(&kvm->mmu_lock);
+
+ for_each_tdp_mmu_root_yield_safe(kvm, root, true) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;
--
2.31.0.291.g576ba9dcdaf-goog