[Qemu-devel] [PATCH] Fix guest OS hangs on boot when 64bit PCI BAR present

[Alexey Korolev]

At the moment may_overlap flag of MemoryRegion structure
is ignored by the address range assignment process.
This may lead to guest OS hangs if critical qemu
resources are overlapped by PCI BARs. For example
ivshmem 64bit PCI BAR may overlap kvm-apic-msi under
certain conditions. This patch adds a rule that the
regions which should not be overlapped are added to the
view first (i.e. having highest priority). The patch
also corrects ivshmem bar resource to be overlapable
which is the default for PCI BARs

Signed-off-by: Alexey Korolev <address@hidden>
---
 hw/ivshmem.c |    2 +-
 memory.c     |   15 ++++++++++-----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/hw/ivshmem.c b/hw/ivshmem.c
index afaf9b3..1770fa3 100644
--- a/hw/ivshmem.c
+++ b/hw/ivshmem.c
@@ -341,7 +341,7 @@ static void create_shared_memory_BAR(IVShmemState *s, int 
fd) {
     memory_region_init_ram_ptr(&s->ivshmem, "ivshmem.bar2",
                                s->ivshmem_size, ptr);
     vmstate_register_ram(&s->ivshmem, &s->dev.qdev);
-    memory_region_add_subregion(&s->bar, 0, &s->ivshmem);
+    memory_region_add_subregion_overlap(&s->bar, 0, &s->ivshmem, 1);
 
     /* region for shared memory */
     pci_register_bar(&s->dev, 2, s->ivshmem_attr, &s->bar);
diff --git a/memory.c b/memory.c
index cd7d5e0..f1119e7 100644
--- a/memory.c
+++ b/memory.c
@@ -475,7 +475,8 @@ static void render_memory_region(FlatView *view,
                                  MemoryRegion *mr,
                                  Int128 base,
                                  AddrRange clip,
-                                 bool readonly)
+                                 bool readonly,
+                                 bool overlap)
 {
     MemoryRegion *subregion;
     unsigned i;
@@ -503,16 +504,16 @@ static void render_memory_region(FlatView *view,
     if (mr->alias) {
         int128_subfrom(&base, int128_make64(mr->alias->addr));
         int128_subfrom(&base, int128_make64(mr->alias_offset));
-        render_memory_region(view, mr->alias, base, clip, readonly);
+        render_memory_region(view, mr->alias, base, clip, readonly, overlap);
         return;
     }
 
     /* Render subregions in priority order. */
     QTAILQ_FOREACH(subregion, &mr->subregions, subregions_link) {
-        render_memory_region(view, subregion, base, clip, readonly);
+        render_memory_region(view, subregion, base, clip, readonly, overlap);
     }
 
-    if (!mr->terminates) {
+    if (mr->may_overlap != overlap || !mr->terminates) {
         return;
     }
 
@@ -567,7 +568,11 @@ static FlatView generate_memory_topology(MemoryRegion *mr)
 
     if (mr) {
         render_memory_region(&view, mr, int128_zero(),
-                             addrrange_make(int128_zero(), int128_2_64()), 
false);
+                             addrrange_make(int128_zero(), int128_2_64()),
+                             false, false);
+        render_memory_region(&view, mr, int128_zero(),
+                             addrrange_make(int128_zero(), int128_2_64()),
+                             false, true);
     }
     flatview_simplify(&view);
 
-- 
1.7.9.5