linux-kernel - [PATCH v2 9/9] KVM: X86: Optimize zapping rmap

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Date:   Fri, 25 Jun 2021 11:34:19 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     peterx@...hat.com, Maxim Levitsky <mlevitsk@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH v2 9/9] KVM: X86: Optimize zapping rmap

Using rmap_get_first() and rmap_remove() for zapping a huge rmap list could be
slow.  The easy way is to travers the rmap list, collecting the a/d bits and
free the slots along the way.

Provide a pte_list_destroy() and do exactly that.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 arch/x86/kvm/mmu/mmu.c | 45 +++++++++++++++++++++++++++++++-----------
 1 file changed, 33 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index ba0258bdebc4..45aac78dcabc 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1014,6 +1014,38 @@ unsigned int pte_list_count(struct kvm_rmap_head *rmap_head)
 	return count;
 }
 
+/* Return true if rmap existed and callback called, false otherwise */
+static bool pte_list_destroy(struct kvm_rmap_head *rmap_head,
+			     int (*callback)(u64 *sptep))
+{
+	struct pte_list_desc *desc, *next;
+	int i;
+
+	if (!rmap_head->val)
+		return false;
+
+	if (!(rmap_head->val & 1)) {
+		if (callback)
+			callback((u64 *)rmap_head->val);
+		goto out;
+	}
+
+	desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
+
+	while (desc) {
+		if (callback)
+			for (i = 0; i < desc->spte_count; i++)
+				callback(desc->sptes[i]);
+		next = desc->more;
+		mmu_free_pte_list_desc(desc);
+		desc = next;
+	}
+out:
+	/* rmap_head is meaningless now, remember to reset it */
+	rmap_head->val = 0;
+	return true;
+}
+
 static struct kvm_rmap_head *__gfn_to_rmap(gfn_t gfn, int level,
 					   struct kvm_memory_slot *slot)
 {
@@ -1403,18 +1435,7 @@ static bool rmap_write_protect(struct kvm_vcpu *vcpu, u64 gfn)
 static bool kvm_zap_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
 			  struct kvm_memory_slot *slot)
 {
-	u64 *sptep;
-	struct rmap_iterator iter;
-	bool flush = false;
-
-	while ((sptep = rmap_get_first(rmap_head, &iter))) {
-		rmap_printk("spte %p %llx.\n", sptep, *sptep);
-
-		pte_list_remove(rmap_head, sptep);
-		flush = true;
-	}
-
-	return flush;
+	return pte_list_destroy(rmap_head, mmu_spte_clear_track_bits);
 }
 
 static bool kvm_unmap_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
-- 
2.31.1