[PATCH 1/2] kvm: Force IOMMU remapping on memory slot read-only flag changes

Alex Williamson
2013-01-24T22:04:03Z

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.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
virt/kvm/kvm_main.c | 28 ++++++++++++++++++++++++----
1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5e709eb..3fec2cd 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 */