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Date:   Thu,  1 Apr 2021 16:37:33 -0700
In-Reply-To: <20210401233736.638171-1-bgardon@google.com>
Message-Id: <20210401233736.638171-11-bgardon@google.com>
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Subject: [PATCH v2 10/13] KVM: x86/mmu: Allow zapping collapsible SPTEs to use
 MMU read lock
From:   Ben Gardon <bgardon@google.com>
To:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>, Peter Xu <peterx@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Peter Shier <pshier@google.com>,
        Peter Feiner <pfeiner@google.com>,
        Junaid Shahid <junaids@google.com>,
        Jim Mattson <jmattson@google.com>,
        Yulei Zhang <yulei.kernel@gmail.com>,
        Wanpeng Li <kernellwp@gmail.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
        Ben Gardon <bgardon@google.com>
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Precedence: bulk

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@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