On Tue, Jul 27, 2021 at 03:21:31PM +0200, David Hildenbrand wrote:
On 23.07.21 21:34, Peter Xu wrote:
Topology update could be wrongly triggered in memory region finalize() if
there's bug somewhere else. It'll be a very confusing stack when it
happens (e.g., sending KVM ioctl within the RCU thread, and we'll observe it
only until it fails!).
Instead of that, we use the push()/pop() helper to avoid memory transaction
commit, at the same time we use assertions to make sure there's no pending
updates or it's a nested transaction, so it could fail even earlier and in a
more explicit way.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
softmmu/memory.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/softmmu/memory.c b/softmmu/memory.c
index 1a3e9ff8ad..dfce4a2bda 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -170,6 +170,12 @@ struct MemoryRegionIoeventfd {
EventNotifier *e;
};
+/* Returns whether there's any pending memory updates */
+static bool memory_region_has_pending_update(void)
+{
+ return memory_region_update_pending || ioeventfd_update_pending;
+}
+
static bool memory_region_ioeventfd_before(MemoryRegionIoeventfd *a,
MemoryRegionIoeventfd *b)
{
@@ -1756,12 +1762,25 @@ static void memory_region_finalize(Object *obj)
* and cause an infinite loop.
*/
mr->enabled = false;
- memory_region_transaction_begin();
+
+ /*
+ * Use push()/pop() instead of begin()/commit() to make sure below block
+ * won't trigger any topology update (which should never happen, but it's
+ * still a safety belt).
+ */
Hmm, I wonder if we can just keep the begin/end semantics and just do an
assertion before doing the commit? Does anything speak against that?
That sounds working too for the case of run_on_cpu and similar, but I think
this patch should be able to cover more. For example, it's possible depth==0
when enter memory_region_finalize(), but some removal of subregions could
further cause memory layout changes. IMHO we should also bail out early for
those cases too. Thanks,