linux-kernel - [PATCH v5 13/13] KVM: Optimize overlapping memslots check

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Date:   Mon, 20 Sep 2021 23:39:01 +0200
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v5 13/13] KVM: Optimize overlapping memslots check

From: "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>

Do a quick lookup for possibly overlapping gfns when creating or moving
a memslot instead of performing a linear scan of the whole memslot set.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
---
 virt/kvm/kvm_main.c | 36 +++++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5fea467d6fec..78dad8c6376f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1667,6 +1667,30 @@ static int kvm_delete_memslot(struct kvm *kvm,
 	return kvm_set_memslot(kvm, mem, old, &new, as_id, KVM_MR_DELETE);
 }
 
+static bool kvm_check_memslot_overlap(struct kvm_memslots *slots,
+				      struct kvm_memory_slot *nslot)
+{
+	int idx = slots->node_idx;
+	gfn_t nend = nslot->base_gfn + nslot->npages;
+	struct rb_node *node;
+
+	kvm_for_each_memslot_in_gfn_range(node, slots, nslot->base_gfn, nend) {
+		struct kvm_memory_slot *cslot;
+		gfn_t cend;
+
+		cslot = container_of(node, struct kvm_memory_slot, gfn_node[idx]);
+		cend = cslot->base_gfn + cslot->npages;
+		if (cslot->id == nslot->id)
+			continue;
+
+		/* kvm_for_each_in_gfn_no_more() guarantees that cslot->base_gfn < nend */
+		if (cend > nslot->base_gfn)
+			return true;
+	}
+
+	return false;
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -1752,16 +1776,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	}
 
 	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
-		int bkt;
-
 		/* Check for overlaps */
-		kvm_for_each_memslot(tmp, bkt, __kvm_memslots(kvm, as_id)) {
-			if (tmp->id == id)
-				continue;
-			if (!((new.base_gfn + new.npages <= tmp->base_gfn) ||
-			      (new.base_gfn >= tmp->base_gfn + tmp->npages)))
-				return -EEXIST;
-		}
+		if (kvm_check_memslot_overlap(__kvm_memslots(kvm, as_id),
+					      &new))
+			return -EEXIST;
 	}
 
 	/* Allocate/free page dirty bitmap as needed */