[Qemu-devel] [PATCH RFC 4/6] kvm: we never have overlapping slots in kvm_set_phys_mem()

[David Hildenbrand]

Due to how flatviews are handled, we will never have overlapping memory
sections in kvm.

address_space_update_topology_pass() will make sure that we will only
get called for

a) an existing memory section for which we only update parameters
(log_start, log_stop).
b) an existing memory section we want to delete (region_del)
c) a brand new memory section we want to add (region_add)

We cannot have overlapping memory sections in kvm as we will first remove
the overlapping sections and then add the ones without conflicts.

Therefore we can remove the complexity for handling prefix and suffix
slots.

Signed-off-by: David Hildenbrand <address@hidden>
---
 accel/kvm/kvm-all.c | 69 +++++++++--------------------------------------------
 1 file changed, 11 insertions(+), 58 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index bec157e..7b45506 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -725,7 +725,7 @@ kvm_check_extension_list(KVMState *s, const 
KVMCapabilityInfo *list)
 static void kvm_set_phys_mem(KVMMemoryListener *kml,
                              MemoryRegionSection *section, bool add)
 {
-    KVMSlot *mem, old;
+    KVMSlot *mem;
     int err;
     MemoryRegion *mr = section->mr;
     bool writeable = !mr->readonly && !mr->rom_device;
@@ -750,28 +750,17 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
     ram = memory_region_get_ram_ptr(mr) + section->offset_within_region +
           (section->offset_within_address_space - start_addr);
 
-    while (1) {
-        mem = kvm_lookup_overlapping_slot(kml, start_addr, start_addr + size);
+    mem = kvm_lookup_matching_slot(kml, start_addr, size);
+    if (!add) {
         if (!mem) {
-            break;
-        }
-
-        if (add && start_addr >= mem->start_addr &&
-            (start_addr + size <= mem->start_addr + mem->memory_size) &&
-            (ram - start_addr == mem->ram - mem->start_addr)) {
-            /* The new slot fits into the existing one and comes with
-             * identical parameters - update flags and done. */
-            kvm_slot_update_flags(kml, mem, mr);
+            g_assert(!memory_region_is_ram(mr) && !writeable && 
!mr->romd_mode);
             return;
         }
-
-        old = *mem;
-
         if (mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
             kvm_physical_sync_dirty_bitmap(kml, section);
         }
 
-        /* unregister the overlapping slot */
+        /* unregister the slot */
         mem->memory_size = 0;
         err = kvm_set_user_memory_region(kml, mem);
         if (err) {
@@ -779,57 +768,21 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
                     __func__, strerror(-err));
             abort();
         }
-
-        /* register prefix slot */
-        if (old.start_addr < start_addr) {
-            mem = kvm_alloc_slot(kml);
-            mem->memory_size = start_addr - old.start_addr;
-            mem->start_addr = old.start_addr;
-            mem->ram = old.ram;
-            mem->flags =  kvm_mem_flags(mr);
-
-            err = kvm_set_user_memory_region(kml, mem);
-            if (err) {
-                fprintf(stderr, "%s: error registering prefix slot: %s\n",
-                        __func__, strerror(-err));
-#ifdef TARGET_PPC
-                fprintf(stderr, "%s: This is probably because your kernel's " \
-                                "PAGE_SIZE is too big. Please try to use 4k " \
-                                "PAGE_SIZE!\n", __func__);
-#endif
-                abort();
-            }
-        }
-
-        /* register suffix slot */
-        if (old.start_addr + old.memory_size > start_addr + size) {
-            ram_addr_t size_delta;
-
-            mem = kvm_alloc_slot(kml);
-            mem->start_addr = start_addr + size;
-            size_delta = mem->start_addr - old.start_addr;
-            mem->memory_size = old.memory_size - size_delta;
-            mem->ram = old.ram + size_delta;
-            mem->flags = kvm_mem_flags(mr);
-
-            err = kvm_set_user_memory_region(kml, mem);
-            if (err) {
-                fprintf(stderr, "%s: error registering suffix slot: %s\n",
-                        __func__, strerror(-err));
-                abort();
-            }
-        }
+        return;
     }
 
-    if (!add) {
+    if (mem) {
+        /* update the slot */
+        kvm_slot_update_flags(kml, mem, mr);
         return;
     }
+
+    /* register the new slot */
     mem = kvm_alloc_slot(kml);
     mem->memory_size = size;
     mem->start_addr = start_addr;
     mem->ram = ram;
     mem->flags = kvm_mem_flags(mr);
-
     err = kvm_set_user_memory_region(kml, mem);
     if (err) {
         fprintf(stderr, "%s: error registering slot: %s\n", __func__,
-- 
2.9.4