linux-kernel - [PATCH v7 27/29] KVM: Optimize overlapping memslots check

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Date:   Mon,  6 Dec 2021 20:54:33 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        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>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Ben Gardon <bgardon@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v7 27/29] 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>
[sean: tweaked params to avoid churn in future cleanup]
Reviewed-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/kvm_main.c | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 086f18969bc3..4cb97b31eac5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1817,6 +1817,19 @@ static int kvm_set_memslot(struct kvm *kvm,
 	return 0;
 }
 
+static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
+				      gfn_t start, gfn_t end)
+{
+	struct kvm_memslot_iter iter;
+
+	kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
+		if (iter.slot->id != id)
+			return true;
+	}
+
+	return false;
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -1828,8 +1841,9 @@ static int kvm_set_memslot(struct kvm *kvm,
 int __kvm_set_memory_region(struct kvm *kvm,
 			    const struct kvm_userspace_memory_region *mem)
 {
-	struct kvm_memory_slot *old, *tmp;
+	struct kvm_memory_slot *old;
 	struct kvm_memory_slot new;
+	struct kvm_memslots *slots;
 	enum kvm_mr_change change;
 	int as_id, id;
 	int r;
@@ -1858,11 +1872,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
 		return -EINVAL;
 
+	slots = __kvm_memslots(kvm, as_id);
+
 	/*
 	 * Note, the old memslot (and the pointer itself!) may be invalidated
 	 * and/or destroyed by kvm_set_memslot().
 	 */
-	old = id_to_memslot(__kvm_memslots(kvm, as_id), id);
+	old = id_to_memslot(slots, id);
 
 	if (!mem->memory_size) {
 		if (!old || !old->npages)
@@ -1911,18 +1927,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			return 0;
 	}
 
-	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 ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) &&
+	    kvm_check_memslot_overlap(slots, id, new.base_gfn,
+				      new.base_gfn + new.npages))
+		return -EEXIST;
 
 	return kvm_set_memslot(kvm, old, &new, change);
 }