KVM: Wait 'til the bitter end to initialize the "new" memslot

Initialize the "new" memslot in the !DELETE path only after the various
sanity checks have passed.  This will allow a future commit to allocate
@new dynamically without having to copy a memslot, and without having to
deal with freeing @new in error paths and in the "nothing to change" path
that's hiding in the sanity checks.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <a084d0531ca3a826a7f861eb2b08b5d1c06ef265.1638817641.git.maciej.szmigiero@oracle.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d27568b3b984ab8eef6206690f73b7f8a6a01e1b..71815e75e41cda0e8bb3ff17022ccf5f5d14fa80 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1843,6 +1843,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
        struct kvm_memory_slot new;
        struct kvm_memslots *slots;
        enum kvm_mr_change change;
+       unsigned long npages;
+       gfn_t base_gfn;
        int as_id, id;
        int r;
 
@@ -1869,6 +1871,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
                return -EINVAL;
        if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
                return -EINVAL;
+       if ((mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
+               return -EINVAL;
 
        slots = __kvm_memslots(kvm, as_id);
 
@@ -1892,15 +1896,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
                return kvm_set_memslot(kvm, old, &new, KVM_MR_DELETE);
        }
 
-       new.as_id = as_id;
-       new.id = id;
-       new.base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
-       new.npages = mem->memory_size >> PAGE_SHIFT;
-       new.flags = mem->flags;
-       new.userspace_addr = mem->userspace_addr;
-
-       if (new.npages > KVM_MEM_MAX_NR_PAGES)
-               return -EINVAL;
+       base_gfn = (mem->guest_phys_addr >> PAGE_SHIFT);
+       npages = (mem->memory_size >> PAGE_SHIFT);
 
        if (!old || !old->npages) {
                change = KVM_MR_CREATE;
@@ -1909,27 +1906,33 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 * To simplify KVM internals, the total number of pages across
                 * all memslots must fit in an unsigned long.
                 */
-               if ((kvm->nr_memslot_pages + new.npages) < kvm->nr_memslot_pages)
+               if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
                        return -EINVAL;
        } else { /* Modify an existing slot. */
-               if ((new.userspace_addr != old->userspace_addr) ||
-                   (new.npages != old->npages) ||
-                   ((new.flags ^ old->flags) & KVM_MEM_READONLY))
+               if ((mem->userspace_addr != old->userspace_addr) ||
+                   (npages != old->npages) ||
+                   ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
                        return -EINVAL;
 
-               if (new.base_gfn != old->base_gfn)
+               if (base_gfn != old->base_gfn)
                        change = KVM_MR_MOVE;
-               else if (new.flags != old->flags)
+               else if (mem->flags != old->flags)
                        change = KVM_MR_FLAGS_ONLY;
                else /* Nothing to change. */
                        return 0;
        }
 
        if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) &&
-           kvm_check_memslot_overlap(slots, id, new.base_gfn,
-                                     new.base_gfn + new.npages))
+           kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages))
                return -EEXIST;
 
+       new.as_id = as_id;
+       new.id = id;
+       new.base_gfn = base_gfn;
+       new.npages = npages;
+       new.flags = mem->flags;
+       new.userspace_addr = mem->userspace_addr;
+
        return kvm_set_memslot(kvm, old, &new, change);
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);