linux-kernel - [RFC 04/19] KVM: x86/mmu: Yield while processing disconnected

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Date:   Wed, 10 Nov 2021 14:29:55 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Kai Huang <kai.huang@...el.com>,
        Keqian Zhu <zhukeqian1@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [RFC 04/19] KVM: x86/mmu: Yield while processing disconnected_sps

When preparing to free disconnected SPs, the list can accumulate many
entries; enough that it is likely necessary to yeild while queuing RCU
callbacks to free the SPs.

Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index a448f0f2d993..c2a9f7acf8ef 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -513,7 +513,8 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
  * being removed from the paging structure and this function being called.
  */
 static void handle_disconnected_sps(struct kvm *kvm,
-				    struct list_head *disconnected_sps)
+				    struct list_head *disconnected_sps,
+				    bool can_yield, bool shared)
 {
 	struct kvm_mmu_page *sp;
 	struct kvm_mmu_page *next;
@@ -521,6 +522,16 @@ static void handle_disconnected_sps(struct kvm *kvm,
 	list_for_each_entry_safe(sp, next, disconnected_sps, link) {
 		list_del(&sp->link);
 		call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback);
+
+		if (can_yield &&
+		    (need_resched() || rwlock_needbreak(&kvm->mmu_lock))) {
+			rcu_read_unlock();
+			if (shared)
+				cond_resched_rwlock_read(&kvm->mmu_lock);
+			else
+				cond_resched_rwlock_write(&kvm->mmu_lock);
+			rcu_read_lock();
+		}
 	}
 }
 
@@ -599,7 +610,7 @@ static inline bool tdp_mmu_zap_spte_atomic(struct kvm *kvm,
 	 */
 	WRITE_ONCE(*rcu_dereference(iter->sptep), 0);
 
-	handle_disconnected_sps(kvm, &disconnected_sps);
+	handle_disconnected_sps(kvm, &disconnected_sps, false, true);
 
 	return true;
 }
@@ -817,7 +828,8 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 
 	if (!list_empty(&disconnected_sps)) {
 		kvm_flush_remote_tlbs(kvm);
-		handle_disconnected_sps(kvm, &disconnected_sps);
+		handle_disconnected_sps(kvm, &disconnected_sps,
+					can_yield, shared);
 		flush = false;
 	}
 
-- 
2.34.0.rc0.344.g81b53c2807-goog