[Qemu-devel] [PATCH RFC 6/6] kvm: kvm_log_sync() is only called with known memory sections

[David Hildenbrand]

Flatview will make sure that we can only end up in this function with
memory sections that correspond to exactly one slot. So we don't
have to iterate multiple times. There won't be overlapping slots but
only matching slots.

Properly align the section and look up the corresponding slot. This
heavily simplifies this function.

We can now get rid of kvm_lookup_overlapping_slot().

Signed-off-by: David Hildenbrand <address@hidden>
---
 accel/kvm/kvm-all.c | 101 +++++++++++++++++-----------------------------------
 1 file changed, 33 insertions(+), 68 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 78a7f01..5f1463d 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -218,34 +218,6 @@ static hwaddr kvm_align_section(MemoryRegionSection 
*section,
     return size;
 }
 
-/*
- * Find overlapping slot with lowest start address
- */
-static KVMSlot *kvm_lookup_overlapping_slot(KVMMemoryListener *kml,
-                                            hwaddr start_addr,
-                                            hwaddr end_addr)
-{
-    KVMState *s = kvm_state;
-    KVMSlot *found = NULL;
-    int i;
-
-    for (i = 0; i < s->nr_slots; i++) {
-        KVMSlot *mem = &kml->slots[i];
-
-        if (mem->memory_size == 0 ||
-            (found && found->start_addr < mem->start_addr)) {
-            continue;
-        }
-
-        if (end_addr > mem->start_addr &&
-            start_addr < mem->start_addr + mem->memory_size) {
-            found = mem;
-        }
-    }
-
-    return found;
-}
-
 int kvm_physical_memory_addr_from_host(KVMState *s, void *ram,
                                        hwaddr *phys_addr)
 {
@@ -489,55 +461,48 @@ static int 
kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
                                           MemoryRegionSection *section)
 {
     KVMState *s = kvm_state;
-    unsigned long size, allocated_size = 0;
     struct kvm_dirty_log d = {};
     KVMSlot *mem;
-    int ret = 0;
-    hwaddr start_addr = section->offset_within_address_space;
-    hwaddr end_addr = start_addr + int128_get64(section->size);
+    hwaddr start_addr, size;
 
-    d.dirty_bitmap = NULL;
-    while (start_addr < end_addr) {
-        mem = kvm_lookup_overlapping_slot(kml, start_addr, end_addr);
-        if (mem == NULL) {
-            break;
-        }
+    size = kvm_align_section(section, &start_addr);
+    if (!size) {
+        return 0;
+    }
 
-        /* XXX bad kernel interface alert
-         * For dirty bitmap, kernel allocates array of size aligned to
-         * bits-per-long.  But for case when the kernel is 64bits and
-         * the userspace is 32bits, userspace can't align to the same
-         * bits-per-long, since sizeof(long) is different between kernel
-         * and user space.  This way, userspace will provide buffer which
-         * may be 4 bytes less than the kernel will use, resulting in
-         * userspace memory corruption (which is not detectable by valgrind
-         * too, in most cases).
-         * So for now, let's align to 64 instead of HOST_LONG_BITS here, in
-         * a hope that sizeof(long) won't become >8 any time soon.
-         */
-        size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
-                     /*HOST_LONG_BITS*/ 64) / 8;
-        if (!d.dirty_bitmap) {
-            d.dirty_bitmap = g_malloc(size);
-        } else if (size > allocated_size) {
-            d.dirty_bitmap = g_realloc(d.dirty_bitmap, size);
-        }
-        allocated_size = size;
-        memset(d.dirty_bitmap, 0, allocated_size);
+    mem = kvm_lookup_matching_slot(kml, start_addr, size);
+    if (!mem) {
+        fprintf(stderr, "%s: error finding slot\n", __func__);
+        abort();
+    }
 
-        d.slot = mem->slot | (kml->as_id << 16);
-        if (kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) == -1) {
-            DPRINTF("ioctl failed %d\n", errno);
-            ret = -1;
-            break;
-        }
+    /* XXX bad kernel interface alert
+     * For dirty bitmap, kernel allocates array of size aligned to
+     * bits-per-long.  But for case when the kernel is 64bits and
+     * the userspace is 32bits, userspace can't align to the same
+     * bits-per-long, since sizeof(long) is different between kernel
+     * and user space.  This way, userspace will provide buffer which
+     * may be 4 bytes less than the kernel will use, resulting in
+     * userspace memory corruption (which is not detectable by valgrind
+     * too, in most cases).
+     * So for now, let's align to 64 instead of HOST_LONG_BITS here, in
+     * a hope that sizeof(long) won't become >8 any time soon.
+     */
+    size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
+                 /*HOST_LONG_BITS*/ 64) / 8;
+    d.dirty_bitmap = g_malloc0(size);
 
-        kvm_get_dirty_pages_log_range(section, d.dirty_bitmap);
-        start_addr = mem->start_addr + mem->memory_size;
+    d.slot = mem->slot | (kml->as_id << 16);
+    if (kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) == -1) {
+        DPRINTF("ioctl failed %d\n", errno);
+        g_free(d.dirty_bitmap);
+        return -1;
     }
+
+    kvm_get_dirty_pages_log_range(section, d.dirty_bitmap);
     g_free(d.dirty_bitmap);
 
-    return ret;
+    return 0;
 }
 
 static void kvm_coalesce_mmio_region(MemoryListener *listener,
-- 
2.9.4