[Qemu-devel] [RFC v1 2/7] memory: limit sections in the radix tree to the actual address space size

[Avi Kivity <avi@redhat.com>]

The radix tree is statically sized to fit TARGET_PHYS_ADDR_SPACE_BITS.
If a larger memory region is registered, it will overflow.

Fix by limiting any section in the radix tree to the supported size.

This problem was not observed earlier since artificial regions (containers
and aliases) are eliminated by the memory core, leaving only device regions
which have reasonable sizes.  An IOMMU however cannot be eliminated by the
memory core, and may have an artificial size.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 exec.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/exec.c b/exec.c
index 4bc79fb..328753d 100644
--- a/exec.c
+++ b/exec.c
@@ -2272,10 +2272,23 @@ static void register_multipage(AddressSpaceDispatch *d, MemoryRegionSection *sec
                   section_index);
 }
 
+static MemoryRegionSection limit(MemoryRegionSection section)
+{
+    unsigned practical_as_bits = MIN(TARGET_PHYS_ADDR_SPACE_BITS, 62);
+    target_phys_addr_t as_limit;
+
+    as_limit = (target_phys_addr_t)1 << practical_as_bits;
+
+    section.size = MIN(section.offset_within_address_space + section.size, as_limit)
+                   - section.offset_within_address_space;
+
+    return section;
+}
+
 static void mem_add(MemoryListener *listener, MemoryRegionSection *section)
 {
     AddressSpaceDispatch *d = container_of(listener, AddressSpaceDispatch, listener);
-    MemoryRegionSection now = *section, remain = *section;
+    MemoryRegionSection now = limit(*section), remain = limit(*section);
 
     if ((now.offset_within_address_space & ~TARGET_PAGE_MASK)
         || (now.size < TARGET_PAGE_SIZE)) {
-- 
1.7.12