[Qemu-devel] [7139] kvm: improve handling of overlapping slots (Jan Kiszka)

[Anthony Liguori]

Revision: 7139
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=7139
Author:   aliguori
Date:     2009-04-17 14:26:33 +0000 (Fri, 17 Apr 2009)
Log Message:
-----------
kvm: improve handling of overlapping slots (Jan Kiszka)

This reworks the slot management to handle more patterns of
cpu_register_physical_memory*, finally allowing to reset KVM guests (so
far address remapping on reset broke the slot management).

We could actually handle all possible ones without failing, but a KVM
kernel bug in older versions would force us to track all previous
fragmentations and maintain them (as that bug prevents registering
larger slots that overlap also deleted ones). To remain backward
compatible but avoid overly complicated workarounds, we apply a simpler
workaround that covers all currently used patterns.

Signed-off-by: Jan Kiszka <address@hidden>
Signed-off-by: Anthony Liguori <address@hidden>

Modified Paths:
--------------
    trunk/kvm-all.c

Modified: trunk/kvm-all.c
===================================================================
--- trunk/kvm-all.c     2009-04-17 14:26:29 UTC (rev 7138)
+++ trunk/kvm-all.c     2009-04-17 14:26:33 UTC (rev 7139)
@@ -98,19 +98,31 @@
     return NULL;
 }
 
-static KVMSlot *kvm_lookup_slot(KVMState *s, target_phys_addr_t start_addr)
+/*
+ * Find overlapping slot with lowest start address
+ */
+static KVMSlot *kvm_lookup_overlapping_slot(KVMState *s,
+                                            target_phys_addr_t start_addr,
+                                            target_phys_addr_t end_addr)
 {
+    KVMSlot *found = NULL;
     int i;
 
     for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
         KVMSlot *mem = &s->slots[i];
 
-        if (start_addr >= mem->start_addr &&
-            start_addr < (mem->start_addr + mem->memory_size))
-            return mem;
+        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 NULL;
+    return found;
 }
 
 static int kvm_set_user_memory_region(KVMState *s, KVMSlot *slot)
@@ -567,7 +579,8 @@
 {
     KVMState *s = kvm_state;
     ram_addr_t flags = phys_offset & ~TARGET_PAGE_MASK;
-    KVMSlot *mem;
+    KVMSlot *mem, old;
+    int err;
 
     if (start_addr & ~TARGET_PAGE_MASK) {
         fprintf(stderr, "Only page-aligned memory slots supported\n");
@@ -577,55 +590,100 @@
     /* KVM does not support read-only slots */
     phys_offset &= ~IO_MEM_ROM;
 
-    mem = kvm_lookup_slot(s, start_addr);
-    if (mem) {
-        if (flags >= IO_MEM_UNASSIGNED) {
-            mem->memory_size = 0;
-            mem->start_addr = start_addr;
-            mem->phys_offset = 0;
+    while (1) {
+        mem = kvm_lookup_overlapping_slot(s, start_addr, start_addr + size);
+        if (!mem) {
+            break;
+        }
+
+        if (flags < IO_MEM_UNASSIGNED && start_addr >= mem->start_addr &&
+            (start_addr + size <= mem->start_addr + mem->memory_size) &&
+            (phys_offset - start_addr == mem->phys_offset - mem->start_addr)) {
+            /* The new slot fits into the existing one and comes with
+             * identical parameters - nothing to be done. */
+            return;
+        }
+
+        old = *mem;
+
+        /* unregister the overlapping slot */
+        mem->memory_size = 0;
+        err = kvm_set_user_memory_region(s, mem);
+        if (err) {
+            fprintf(stderr, "%s: error unregistering overlapping slot: %s\n",
+                    __func__, strerror(-err));
+            abort();
+        }
+
+        /* Workaround for older KVM versions: we can't join slots, even not by
+         * unregistering the previous ones and then registering the larger
+         * slot. We have to maintain the existing fragmentation. Sigh.
+         *
+         * This workaround assumes that the new slot starts at the same
+         * address as the first existing one. If not or if some overlapping
+         * slot comes around later, we will fail (not seen in practice so far)
+         * - and actually require a recent KVM version. */
+        if (old.start_addr == start_addr && old.memory_size < size &&
+            flags < IO_MEM_UNASSIGNED) {
+            mem = kvm_alloc_slot(s);
+            mem->memory_size = old.memory_size;
+            mem->start_addr = old.start_addr;
+            mem->phys_offset = old.phys_offset;
             mem->flags = 0;
 
-            kvm_set_user_memory_region(s, mem);
-        } else if (start_addr >= mem->start_addr &&
-                   (start_addr + size) <= (mem->start_addr +
-                                           mem->memory_size)) {
-            KVMSlot slot;
-            target_phys_addr_t mem_start;
-            ram_addr_t mem_size, mem_offset;
+            err = kvm_set_user_memory_region(s, mem);
+            if (err) {
+                fprintf(stderr, "%s: error updating slot: %s\n", __func__,
+                        strerror(-err));
+                abort();
+            }
 
-            /* Not splitting */
-            if ((phys_offset - (start_addr - mem->start_addr)) == 
-                mem->phys_offset)
-                return;
+            start_addr += old.memory_size;
+            phys_offset += old.memory_size;
+            size -= old.memory_size;
+            continue;
+        }
 
-            /* unregister whole slot */
-            memcpy(&slot, mem, sizeof(slot));
-            mem->memory_size = 0;
-            kvm_set_user_memory_region(s, mem);
+        /* register prefix slot */
+        if (old.start_addr < start_addr) {
+            mem = kvm_alloc_slot(s);
+            mem->memory_size = start_addr - old.start_addr;
+            mem->start_addr = old.start_addr;
+            mem->phys_offset = old.phys_offset;
+            mem->flags = 0;
 
-            /* register prefix slot */
-            mem_start = slot.start_addr;
-            mem_size = start_addr - slot.start_addr;
-            mem_offset = slot.phys_offset;
-            if (mem_size)
-                kvm_set_phys_mem(mem_start, mem_size, mem_offset);
+            err = kvm_set_user_memory_region(s, mem);
+            if (err) {
+                fprintf(stderr, "%s: error registering prefix slot: %s\n",
+                        __func__, strerror(-err));
+                abort();
+            }
+        }
 
-            /* register new slot */
-            kvm_set_phys_mem(start_addr, size, phys_offset);
+        /* register suffix slot */
+        if (old.start_addr + old.memory_size > start_addr + size) {
+            ram_addr_t size_delta;
 
-            /* register suffix slot */
-            mem_start = start_addr + size;
-            mem_offset += mem_size + size;
-            mem_size = slot.memory_size - mem_size - size;
-            if (mem_size)
-                kvm_set_phys_mem(mem_start, mem_size, mem_offset);
+            mem = kvm_alloc_slot(s);
+            mem->start_addr = start_addr + size;
+            size_delta = mem->start_addr - old.start_addr;
+            mem->memory_size = old.memory_size - size_delta;
+            mem->phys_offset = old.phys_offset + size_delta;
+            mem->flags = 0;
 
-            return;
-        } else {
-            printf("Registering overlapping slot\n");
-            abort();
+            err = kvm_set_user_memory_region(s, mem);
+            if (err) {
+                fprintf(stderr, "%s: error registering suffix slot: %s\n",
+                        __func__, strerror(-err));
+                abort();
+            }
         }
     }
+
+    /* in case the KVM bug workaround already "consumed" the new slot */
+    if (!size)
+        return;
+
     /* KVM does not need to know about this memory */
     if (flags >= IO_MEM_UNASSIGNED)
         return;
@@ -636,8 +694,12 @@
     mem->phys_offset = phys_offset;
     mem->flags = 0;
 
-    kvm_set_user_memory_region(s, mem);
-    /* FIXME deal with errors */
+    err = kvm_set_user_memory_region(s, mem);
+    if (err) {
+        fprintf(stderr, "%s: error registering slot: %s\n", __func__,
+                strerror(-err));
+        abort();
+    }
 }
 
 int kvm_ioctl(KVMState *s, int type, ...)