linux-kernel - [PATCH 01/18] KVM: x86/mmu: Coalesce TDP MMU TLB flushes when zapping collapsible SPTEs

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Message-Id: <20210326021957.1424875-2-seanjc@google.com>
Date:   Thu, 25 Mar 2021 19:19:40 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 01/18] KVM: x86/mmu: Coalesce TDP MMU TLB flushes when zapping
 collapsible SPTEs

When zapping collapsible SPTEs across multiple roots, gather pending
flushes and perform a single remote TLB flush at the end, as opposed to
flushing after processing every root.

Note, flush may be cleared by the result of zap_collapsible_spte_range().
This is intended and correct, e.g. yielding may have serviced a prior
pending flush.

Cc: Ben Gardon <bgardon@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 08667e3cf091..463f1be6ff0d 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1278,21 +1278,21 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
  * Clear leaf entries which could be replaced by large mappings, for
  * GFNs within the slot.
  */
-static void zap_collapsible_spte_range(struct kvm *kvm,
+static bool zap_collapsible_spte_range(struct kvm *kvm,
 				       struct kvm_mmu_page *root,
-				       struct kvm_memory_slot *slot)
+				       struct kvm_memory_slot *slot,
+				       bool flush)
 {
 	gfn_t start = slot->base_gfn;
 	gfn_t end = start + slot->npages;
 	struct tdp_iter iter;
 	kvm_pfn_t pfn;
-	bool spte_set = false;
 
 	rcu_read_lock();
 
 	tdp_root_for_each_pte(iter, root, start, end) {
-		if (tdp_mmu_iter_cond_resched(kvm, &iter, spte_set)) {
-			spte_set = false;
+		if (tdp_mmu_iter_cond_resched(kvm, &iter, flush)) {
+			flush = false;
 			continue;
 		}
 
@@ -1308,12 +1308,12 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
 
 		tdp_mmu_set_spte(kvm, &iter, 0);
 
-		spte_set = true;
+		flush = true;
 	}
 
 	rcu_read_unlock();
-	if (spte_set)
-		kvm_flush_remote_tlbs(kvm);
+
+	return flush;
 }
 
 /*
@@ -1324,6 +1324,7 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
 				       struct kvm_memory_slot *slot)
 {
 	struct kvm_mmu_page *root;
+	bool flush = false;
 	int root_as_id;
 
 	for_each_tdp_mmu_root_yield_safe(kvm, root) {
@@ -1331,8 +1332,11 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
 		if (root_as_id != slot->as_id)
 			continue;
 
-		zap_collapsible_spte_range(kvm, root, slot);
+		flush = zap_collapsible_spte_range(kvm, root, slot, flush);
 	}
+
+	if (flush)
+		kvm_flush_remote_tlbs(kvm);
 }
 
 /*
-- 
2.31.0.291.g576ba9dcdaf-goog