KVM: Fix overlapping check for memory slots

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@kernel.org
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 0424326f167963d5b764554ebec95029b8b99439..c344599d1be0ee1d47a92c125ae7fe9a86859dc1 100644 (file)
--- 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

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e02c48ba2224166e7f2160d5a5d487e18a9ececa..d85642e2c74d9b93b67b881279a464e568fe2301 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1005,7 +1005,7 @@ int __kvm_set_memory_region(struct kvm *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_extension_generic(long arg)
        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;