linux-kernel - [PATCH] kvm: Fix user memslot overlap check

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Message-ID: <20121129204619.8862.77695.stgit@bling.home>
Date:	Thu, 29 Nov 2012 13:48:17 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	mtosatti@...hat.com, gleb@...hat.com
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	xiaoguangrong@...ux.vnet.ibm.com
Subject: [PATCH] kvm: Fix user memslot overlap check

Prior to memory slot sorting this loop compared all of the user memory
slots for overlap with new entries.  With memory slot sorting, we're
just checking some number of entries in the array that may or may not
be user slots.  Instead, walk all the slots with kvm_for_each_memslot,
which has the added benefit of terminating early when we hit the first
empty slot, and skip comparison to private slots.

Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
Cc: stable@...r.kernel.org
---
 virt/kvm/kvm_main.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index be70035..cac294d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -710,7 +710,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	gfn_t base_gfn;
 	unsigned long npages;
 	unsigned long i;
-	struct kvm_memory_slot *memslot;
+	struct kvm_memory_slot *memslot, *slot;
 	struct kvm_memory_slot old, new;
 	struct kvm_memslots *slots, *old_memslots;
 
@@ -761,13 +761,11 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
 	/* Check for overlaps */
 	r = -EEXIST;
-	for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
-		struct kvm_memory_slot *s = &kvm->memslots->memslots[i];
-
-		if (s == memslot || !s->npages)
+	kvm_for_each_memslot(slot, kvm->memslots) {
+		if (slot->id >= KVM_MEMORY_SLOTS || slot == memslot)
 			continue;
-		if (!((base_gfn + npages <= s->base_gfn) ||
-		      (base_gfn >= s->base_gfn + s->npages)))
+		if (!((base_gfn + npages <= slot->base_gfn) ||
+		      (base_gfn >= slot->base_gfn + slot->npages)))
 			goto out_free;
 	}
 

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