cpu: Support a target CPU having a variable page size
Support target CPUs having a page size which isn't knownn
at compile time. To use this, the CPU implementation should:
* define TARGET_PAGE_BITS_VARY
* not define TARGET_PAGE_BITS
* define TARGET_PAGE_BITS_MIN to the smallest value it
might possibly want for TARGET_PAGE_BITS
* call set_preferred_target_page_bits() in its realize
function to indicate the actual preferred target page
size for the CPU (and report any error from it)
In CONFIG_USER_ONLY, the CPU implementation should continue
to define TARGET_PAGE_BITS appropriately for the guest
OS page size.
Machines which want to take advantage of having the page
size something larger than TARGET_PAGE_BITS_MIN must
set the MachineClass minimum_page_bits field to a value
which they guarantee will be no greater than the preferred
page size for any CPU they create.
Note that changing the target page size by setting
minimum_page_bits is a migration compatibility break
for that machine.
For debugging purposes, attempts to use TARGET_PAGE_SIZE
before it has been finally confirmed will assert.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
diff --git a/exec.c b/exec.c
index 93128fd..963b91a 100644
--- a/exec.c
+++ b/exec.c
@@ -93,6 +93,11 @@
#endif
+#ifdef TARGET_PAGE_BITS_VARY
+int target_page_bits;
+bool target_page_bits_decided;
+#endif
+
struct CPUTailQ cpus = QTAILQ_HEAD_INITIALIZER(cpus);
/* current CPU in the current thread. It is only valid inside
cpu_exec() */
@@ -102,8 +107,37 @@
2 = Adaptive rate instruction counting. */
int use_icount;
+bool set_preferred_target_page_bits(int bits)
+{
+ /* The target page size is the lowest common denominator for all
+ * the CPUs in the system, so we can only make it smaller, never
+ * larger. And we can't make it smaller once we've committed to
+ * a particular size.
+ */
+#ifdef TARGET_PAGE_BITS_VARY
+ assert(bits >= TARGET_PAGE_BITS_MIN);
+ if (target_page_bits == 0 || target_page_bits > bits) {
+ if (target_page_bits_decided) {
+ return false;
+ }
+ target_page_bits = bits;
+ }
+#endif
+ return true;
+}
+
#if !defined(CONFIG_USER_ONLY)
+static void finalize_target_page_bits(void)
+{
+#ifdef TARGET_PAGE_BITS_VARY
+ if (target_page_bits == 0) {
+ target_page_bits = TARGET_PAGE_BITS_MIN;
+ }
+ target_page_bits_decided = true;
+#endif
+}
+
typedef struct PhysPageEntry PhysPageEntry;
struct PhysPageEntry {
@@ -2807,6 +2841,14 @@
void cpu_exec_init_all(void)
{
qemu_mutex_init(&ram_list.mutex);
+ /* The data structures we set up here depend on knowing the page size,
+ * so no more changes can be made after this point.
+ * In an ideal world, nothing we did before we had finished the
+ * machine setup would care about the target page size, and we could
+ * do this much later, rather than requiring board models to state
+ * up front what their requirements are.
+ */
+ finalize_target_page_bits();
io_mem_init();
memory_map_init();
qemu_mutex_init(&map_client_list_lock);
