path: root/exec.c
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authorPeter Maydell <peter.maydell@linaro.org>2016-10-24 16:26:49 +0100
committerPeter Maydell <peter.maydell@linaro.org>2016-10-24 16:26:49 +0100
commit20bccb82ff3ea09bcb7c4ee226d3160cab15f7da (patch)
treebeb472fa034fe9e742c571f678982235695f29eb /exec.c
parent66ec9f49399f0a9fa13ee77c472caba0de2773fc (diff)
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>
Diffstat (limited to 'exec.c')
1 files changed, 42 insertions, 0 deletions
diff --git a/exec.c b/exec.c
index 93128fd19a..963b91a018 100644
--- a/exec.c
+++ b/exec.c
@@ -93,6 +93,11 @@ static MemoryRegion io_mem_unassigned;
+int target_page_bits;
+bool target_page_bits_decided;
struct CPUTailQ cpus = QTAILQ_HEAD_INITIALIZER(cpus);
/* current CPU in the current thread. It is only valid inside
cpu_exec() */
@@ -102,8 +107,37 @@ __thread CPUState *current_cpu;
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.
+ */
+ 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;
+ }
+ return true;
#if !defined(CONFIG_USER_ONLY)
+static void finalize_target_page_bits(void)
+ if (target_page_bits == 0) {
+ target_page_bits = TARGET_PAGE_BITS_MIN;
+ }
+ target_page_bits_decided = true;
typedef struct PhysPageEntry PhysPageEntry;
struct PhysPageEntry {
@@ -2807,6 +2841,14 @@ void cpu_register_map_client(QEMUBH *bh)
void cpu_exec_init_all(void)
+ /* 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();