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>

1 files changed, 24 insertions, 4 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5e709ebb7c40..3fec2cdd951b 100644
--- 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 */