[patch 10/58] KVM: Fix overlapping check for memory slots

[Greg KH]

2.6.29-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Jan Kiszka <jan.kiszka@xxxxxx>

upstream commit: 4cd481f68dde99ac416003b825c835f71e364393

When checking for overlapping slots on registration of a new one, kvm
currently also considers zero-length (ie. deleted) slots and rejects
requests incorrectly. This finally denies user space from joining slots.
Fix the check by skipping deleted slots and advertise this via a
KVM_CAP_JOIN_MEMORY_REGIONS_WORKS.

Cc: stable@xxxxxxxxxx
Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
---
 include/linux/kvm.h |    2 ++
 virt/kvm/kvm_main.c |    3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -396,6 +396,8 @@ struct kvm_trace_rec {
 #ifdef __KVM_HAVE_USER_NMI
 #define KVM_CAP_USER_NMI 22
 #endif
+/* Another bug in KVM_SET_USER_MEMORY_REGION fixed: */
+#define KVM_CAP_JOIN_MEMORY_REGIONS_WORKS 30
 
 /*
  * ioctls for VM fds
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1005,7 +1005,7 @@ int __kvm_set_memory_region(struct kvm *
 	for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
 		struct kvm_memory_slot *s = &kvm->memslots[i];
 
-		if (s == memslot)
+		if (s == memslot || !s->npages)
 			continue;
 		if (!((base_gfn + npages <= s->base_gfn) ||
 		      (base_gfn >= s->base_gfn + s->npages)))
@@ -1997,6 +1997,7 @@ static long kvm_dev_ioctl_check_extensio
 	switch (arg) {
 	case KVM_CAP_USER_MEMORY:
 	case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
+	case KVM_CAP_JOIN_MEMORY_REGIONS_WORKS:
 		return 1;
 	default:
 		break;


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