[PATCH v2 10/13] KVM: x86/mmu: Allow zapping collapsible SPTEs to use MMU read lock

[Ben Gardon]

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 <bgar...@google.com>
---
 arch/x86/kvm/mmu/mmu.c     | 14 ++++++++++----
 arch/x86/kvm/mmu/tdp_mmu.c | 17 +++++++++++++----
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d03a7a8b7ea2..5939813e3043 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5612,13 +5612,19 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
        write_lock(&kvm->mmu_lock);
        flush = slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
 
-       if (is_tdp_mmu_enabled(kvm))
-               flush = kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot, flush);
-
        if (flush)
                kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
-
        write_unlock(&kvm->mmu_lock);
+
+       if (is_tdp_mmu_enabled(kvm)) {
+               flush = false;
+
+               read_lock(&kvm->mmu_lock);
+               flush = kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot, flush);
+               if (flush)
+                       kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
+               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 6917403484ce..0e6ffa04e5e1 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1323,7 +1323,8 @@ static bool 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, flush, false)) {
+retry:
+               if (tdp_mmu_iter_cond_resched(kvm, &iter, flush, true)) {
                        flush = false;
                        continue;
                }
@@ -1338,8 +1339,14 @@ static bool 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;
+               }
                flush = true;
        }
 
@@ -1358,7 +1365,9 @@ bool kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
 {
        struct kvm_mmu_page *root;
 
-       for_each_tdp_mmu_root_yield_safe(kvm, root, slot->as_id, false)
+       lockdep_assert_held_read(&kvm->mmu_lock);
+
+       for_each_tdp_mmu_root_yield_safe(kvm, root, slot->as_id, true)
                flush = zap_collapsible_spte_range(kvm, root, slot, flush);
 
        return flush;
-- 
2.31.0.208.g409f899ff0-goog