kvm: Force IOMMU remapping on memory slot read-only flag changes

Memory slot flags can be altered without changing other parameters of
the slot.  The read-only attribute is the only one the IOMMU cares
about, so generate an un-map, re-map when this occurs.  This also
avoid unnecessarily re-mapping the slot when no IOMMU visible changes
are made.

Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5e709eb..3fec2cd 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -731,6 +731,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
        struct kvm_memory_slot *slot;
        struct kvm_memory_slot old, new;
        struct kvm_memslots *slots = NULL, *old_memslots;
+       bool old_iommu_mapped;
 
        r = check_memory_region_flags(mem);
        if (r)
@@ -772,6 +773,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
        new.npages = npages;
        new.flags = mem->flags;
 
+       old_iommu_mapped = old.npages;
+
        /*
         * Disallow changing a memory slot's size or changing anything about
         * zero sized slots that doesn't involve making them non-zero.
@@ -835,6 +838,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
                /* slot was deleted or moved, clear iommu mapping */
                kvm_iommu_unmap_pages(kvm, &old);
+               old_iommu_mapped = false;
                /* From this point no new shadow pages pointing to a deleted,
                 * or moved, memslot will be created.
                 *
@@ -863,11 +867,27 @@ int __kvm_set_memory_region(struct kvm *kvm,
                        goto out_free;
        }
 
-       /* map new memory slot into the iommu */
+       /*
+        * IOMMU mapping:  New slots need to be mapped.  Old slots need to be
+        * un-mapped and re-mapped if their base changes or if flags that the
+        * iommu cares about change (read-only).  Base change unmapping is
+        * handled above with slot deletion, so we only unmap incompatible
+        * flags here.  Anything else the iommu might care about for existing
+        * slots (size changes, userspace addr changes) is disallowed above,
+        * so any other attribute changes getting here can be skipped.
+        */
        if (npages) {
-               r = kvm_iommu_map_pages(kvm, &new);
-               if (r)
-                       goto out_slots;
+               if (old_iommu_mapped &&
+                   ((new.flags ^ old.flags) & KVM_MEM_READONLY)) {
+                       kvm_iommu_unmap_pages(kvm, &old);
+                       old_iommu_mapped = false;
+               }
+
+               if (!old_iommu_mapped) {
+                       r = kvm_iommu_map_pages(kvm, &new);
+                       if (r)
+                               goto out_slots;
+               }
        }
 
        /* actual memory is freed via old in kvm_free_physmem_slot below */