commit 6c090d4a755bb6245461450869130a517e18a3dc
author Shannon Zhao <zhaoshenglong@huawei.com> Wed May 16 17:18:34 2018 +0800
committer Paolo Bonzini <pbonzini@redhat.com> Thu Jun 28 19:05:31 2018 +0200
tree 18a6be0c6933889b0e064934179a963da4adcc3e
parent 61362b71c105ccb151ca16897a7d56534423f390

kvm: Delete the slot if and only if the KVM_MEM_READONLY flag is changed

According to KVM commit 75d61fbc, it needs to delete the slot before
changing the KVM_MEM_READONLY flag. But QEMU commit 235e8982 only check
whether KVM_MEM_READONLY flag is set instead of changing. It doesn't
need to delete the slot if the KVM_MEM_READONLY flag is not changed.

This fixes a issue that migrating a VM at the OVMF startup stage and
VM is executing the codes in rom. Between the deleting and adding the
slot in kvm_set_user_memory_region, there is a chance that guest access
rom and trap to KVM, then KVM can't find the corresponding memslot.
While KVM (on ARM) injects an abort to guest due to the broken hva, then
guest will get stuck.

Signed-off-by: Shannon Zhao <zhaoshenglong@huawei.com>
Message-Id: <1526462314-19720-1-git-send-email-zhaoshenglong@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/kvm/kvm-all.c

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index ffee68e..eb7db92 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -256,7 +256,7 @@
     return 0;
 }
 
-static int kvm_set_user_memory_region(KVMMemoryListener *kml, KVMSlot *slot)
+static int kvm_set_user_memory_region(KVMMemoryListener *kml, KVMSlot *slot, bool new)
 {
     KVMState *s = kvm_state;
     struct kvm_userspace_memory_region mem;
@@ -267,7 +267,7 @@
     mem.userspace_addr = (unsigned long)slot->ram;
     mem.flags = slot->flags;
 
-    if (slot->memory_size && mem.flags & KVM_MEM_READONLY) {
+    if (slot->memory_size && !new && (mem.flags ^ slot->old_flags) & KVM_MEM_READONLY) {
         /* Set the slot size to 0 before setting the slot to the desired
          * value. This is needed based on KVM commit 75d61fbc. */
         mem.memory_size = 0;
@@ -275,6 +275,7 @@
     }
     mem.memory_size = slot->memory_size;
     ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
+    slot->old_flags = mem.flags;
     trace_kvm_set_user_memory(mem.slot, mem.flags, mem.guest_phys_addr,
                               mem.memory_size, mem.userspace_addr, ret);
     return ret;
@@ -391,17 +392,14 @@
 static int kvm_slot_update_flags(KVMMemoryListener *kml, KVMSlot *mem,
                                  MemoryRegion *mr)
 {
-    int old_flags;
-
-    old_flags = mem->flags;
     mem->flags = kvm_mem_flags(mr);
 
     /* If nothing changed effectively, no need to issue ioctl */
-    if (mem->flags == old_flags) {
+    if (mem->flags == mem->old_flags) {
         return 0;
     }
 
-    return kvm_set_user_memory_region(kml, mem);
+    return kvm_set_user_memory_region(kml, mem, false);
 }
 
 static int kvm_section_update_flags(KVMMemoryListener *kml,
@@ -755,7 +753,8 @@
 
         /* unregister the slot */
         mem->memory_size = 0;
-        err = kvm_set_user_memory_region(kml, mem);
+        mem->flags = 0;
+        err = kvm_set_user_memory_region(kml, mem, false);
         if (err) {
             fprintf(stderr, "%s: error unregistering slot: %s\n",
                     __func__, strerror(-err));
@@ -771,7 +770,7 @@
     mem->ram = ram;
     mem->flags = kvm_mem_flags(mr);
 
-    err = kvm_set_user_memory_region(kml, mem);
+    err = kvm_set_user_memory_region(kml, mem, true);
     if (err) {
         fprintf(stderr, "%s: error registering slot: %s\n", __func__,
                 strerror(-err));

include/sysemu/kvm_int.h

diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
index 888557a..f838412 100644
--- a/include/sysemu/kvm_int.h
+++ b/include/sysemu/kvm_int.h
@@ -20,6 +20,7 @@
     void *ram;
     int slot;
     int flags;
+    int old_flags;
 } KVMSlot;
 
 typedef struct KVMMemoryListener {