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.

Backports commit 20bccb82ff3ea09bcb7c4ee226d3160cab15f7da from qemu

include/uc_priv.h

@@ -184,6 +184,9 @@ struct uc_struct {
     RAMList ram_list;
     // Renamed from "alloc_hint" in qemu.
     unsigned phys_map_node_alloc_hint;
+    // Used when a target's page bits can vary
+    int target_page_bits;
+    bool target_page_bits_decided;
 
     // qemu/cpu-exec.c
     BounceBuffer bounce;

qemu/aarch64.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_aarch64
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_aarch64
 #define set_flush_to_zero set_flush_to_zero_aarch64
+#define set_preferred_target_page_bits set_preferred_target_page_bits_aarch64
 #define set_swi_errno set_swi_errno_aarch64
 #define sextract32 sextract32_aarch64
 #define sextract64 sextract64_aarch64

qemu/aarch64eb.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_aarch64eb
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_aarch64eb
 #define set_flush_to_zero set_flush_to_zero_aarch64eb
+#define set_preferred_target_page_bits set_preferred_target_page_bits_aarch64eb
 #define set_swi_errno set_swi_errno_aarch64eb
 #define sextract32 sextract32_aarch64eb
 #define sextract64 sextract64_aarch64eb

qemu/arm.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_arm
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_arm
 #define set_flush_to_zero set_flush_to_zero_arm
+#define set_preferred_target_page_bits set_preferred_target_page_bits_arm
 #define set_swi_errno set_swi_errno_arm
 #define sextract32 sextract32_arm
 #define sextract64 sextract64_arm

qemu/armeb.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_armeb
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_armeb
 #define set_flush_to_zero set_flush_to_zero_armeb
+#define set_preferred_target_page_bits set_preferred_target_page_bits_armeb
 #define set_swi_errno set_swi_errno_armeb
 #define sextract32 sextract32_armeb
 #define sextract64 sextract64_armeb

qemu/exec.c

@@ -68,11 +68,40 @@
 
 #endif
 
+bool set_preferred_target_page_bits(struct uc_struct *uc, 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 (uc->target_page_bits == 0 || uc->target_page_bits > bits) {
+        if (uc->target_page_bits_decided) {
+            return false;
+        }
+        uc->target_page_bits = bits;
+    }
+#endif
+    return true;
+}
+
 #if !defined(CONFIG_USER_ONLY)
 /* current CPU in the current thread. It is only valid inside
    cpu_exec() */
 //DEFINE_TLS(CPUState *, current_cpu);
 
+static void finalize_target_page_bits(struct uc_struct *uc)
+{
+#ifdef TARGET_PAGE_BITS_VARY
+    if (uc->target_page_bits == 0) {
+        uc->target_page_bits = TARGET_PAGE_BITS_MIN;
+    }
+    uc->target_page_bits_decided = true;
+#endif
+}
+
 typedef struct PhysPageEntry PhysPageEntry;
 
 struct PhysPageEntry {
@@ -1826,6 +1855,14 @@ static void memory_map_init(struct uc_struct *uc)
 
 void cpu_exec_init_all(struct uc_struct *uc)
 {
+    /* 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(uc);
     io_mem_init(uc);
 #if !defined(CONFIG_USER_ONLY)
     memory_map_init(uc);

qemu/header_gen.py

@@ -2591,6 +2591,7 @@ symbols = (
     'set_float_rounding_mode',
     'set_flush_inputs_to_zero',
     'set_flush_to_zero',
+    'set_preferred_target_page_bits',
     'set_swi_errno',
     'sextract32',
     'sextract64',

qemu/include/exec/cpu-all.h

@@ -230,6 +230,13 @@ void address_space_stq(AddressSpace *as, hwaddr addr, uint64_t val,
 
 /* page related stuff */
 
+#ifdef TARGET_PAGE_BITS_VARY
+#define TARGET_PAGE_BITS ({ assert(target_page_bits_decided); \
+                            target_page_bits; })
+#else
+#define TARGET_PAGE_BITS_MIN TARGET_PAGE_BITS
+#endif
+
 #define TARGET_PAGE_SIZE (1 << TARGET_PAGE_BITS)
 #define TARGET_PAGE_MASK ~(TARGET_PAGE_SIZE - 1)
 #define TARGET_PAGE_ALIGN(addr) (((addr) + TARGET_PAGE_SIZE - 1) & TARGET_PAGE_MASK)

qemu/include/hw/boards.h

@@ -22,6 +22,7 @@ struct QEMUMachine {
     int max_cpus;
     int is_default;
     int arch;
+    int minimum_page_bits;
 };
 
 void memory_region_allocate_system_memory(MemoryRegion *mr, Object *owner,
@@ -46,6 +47,12 @@ MachineClass *find_default_machine(struct uc_struct *uc, int arch);
 /**
  * MachineClass:
  * @qemu_machine: #QEMUMachine
+ * @minimum_page_bits:
+ *    If non-zero, the board promises never to create a CPU with a page size
+ *    smaller than this, so QEMU can use a more efficient larger page
+ *    size than the target architecture's minimum. (Attempting to create
+ *    such a CPU will fail.) Note that changing this is a migration
+ *    compatibility break for the machine.
  */
 struct MachineClass {
     /*< private >*/
@@ -61,6 +68,7 @@ struct MachineClass {
     int max_cpus;
     int is_default;
     int arch;
+    int minimum_page_bits;
 };
 
 /**

qemu/include/qemu-common.h

@@ -66,6 +66,18 @@ bool tcg_enabled(struct uc_struct *uc);
 struct uc_struct;
 void cpu_exec_init_all(struct uc_struct *uc);
 
+/**
+ * set_preferred_target_page_bits:
+ * @bits: number of bits needed to represent an address within the page
+ *
+ * Set the preferred target page size (the actual target page
+ * size may be smaller than any given CPU's preference).
+ * Returns true on success, false on failure (which can only happen
+ * if this is called after the system has already finalized its
+ * choice of page size and the requested page size is smaller than that).
+ */
+bool set_preferred_target_page_bits(struct uc_struct *uc, int bits);
+
 #include "qemu/module.h"
 
 // support for calling functions before main code is executed.

qemu/m68k.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_m68k
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_m68k
 #define set_flush_to_zero set_flush_to_zero_m68k
+#define set_preferred_target_page_bits set_preferred_target_page_bits_m68k
 #define set_swi_errno set_swi_errno_m68k
 #define sextract32 sextract32_m68k
 #define sextract64 sextract64_m68k

qemu/mips.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_mips
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_mips
 #define set_flush_to_zero set_flush_to_zero_mips
+#define set_preferred_target_page_bits set_preferred_target_page_bits_mips
 #define set_swi_errno set_swi_errno_mips
 #define sextract32 sextract32_mips
 #define sextract64 sextract64_mips

qemu/mips64.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_mips64
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_mips64
 #define set_flush_to_zero set_flush_to_zero_mips64
+#define set_preferred_target_page_bits set_preferred_target_page_bits_mips64
 #define set_swi_errno set_swi_errno_mips64
 #define sextract32 sextract32_mips64
 #define sextract64 sextract64_mips64

qemu/mips64el.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_mips64el
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_mips64el
 #define set_flush_to_zero set_flush_to_zero_mips64el
+#define set_preferred_target_page_bits set_preferred_target_page_bits_mips64el
 #define set_swi_errno set_swi_errno_mips64el
 #define sextract32 sextract32_mips64el
 #define sextract64 sextract64_mips64el

qemu/mipsel.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_mipsel
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_mipsel
 #define set_flush_to_zero set_flush_to_zero_mipsel
+#define set_preferred_target_page_bits set_preferred_target_page_bits_mipsel
 #define set_swi_errno set_swi_errno_mipsel
 #define sextract32 sextract32_mipsel
 #define sextract64 sextract64_mipsel

qemu/powerpc.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_powerpc
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_powerpc
 #define set_flush_to_zero set_flush_to_zero_powerpc
+#define set_preferred_target_page_bits set_preferred_target_page_bits_powerpc
 #define set_swi_errno set_swi_errno_powerpc
 #define sextract32 sextract32_powerpc
 #define sextract64 sextract64_powerpc

qemu/sparc.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_sparc
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_sparc
 #define set_flush_to_zero set_flush_to_zero_sparc
+#define set_preferred_target_page_bits set_preferred_target_page_bits_sparc
 #define set_swi_errno set_swi_errno_sparc
 #define sextract32 sextract32_sparc
 #define sextract64 sextract64_sparc

qemu/sparc64.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_sparc64
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_sparc64
 #define set_flush_to_zero set_flush_to_zero_sparc64
+#define set_preferred_target_page_bits set_preferred_target_page_bits_sparc64
 #define set_swi_errno set_swi_errno_sparc64
 #define sextract32 sextract32_sparc64
 #define sextract64 sextract64_sparc64

qemu/vl.c

@@ -136,6 +136,20 @@ int machine_initialize(struct uc_struct *uc)
                     OBJECT_CLASS(machine_class))));
     uc->machine_state = current_machine;
     current_machine->uc = uc;
+
+    // Unicorn: FIXME: this should be uncommented
+    //          However due to the "stellar" way unicorn
+    //          handles multiple targets (e.g. the YOLO
+    //          Python script named header_gen.py), this
+    //          results in a compilation error.
+    //if (machine_class->minimum_page_bits) {
+    //    if (!set_preferred_target_page_bits(uc, machine_class->minimum_page_bits)) {
+    //        /* This would be a board error: specifying a minimum smaller than
+    //         * a target's compile-time fixed setting.
+    //         */
+    //        g_assert_not_reached();
+    //    }
+    //}
     uc->cpu_exec_init_all(uc);
 
     machine_class->max_cpus = 1;
@@ -168,6 +182,7 @@ static void machine_class_init(struct uc_struct *uc, ObjectClass *oc, void *data
     mc->max_cpus = qm->max_cpus;
     mc->is_default = qm->is_default;
     mc->arch = qm->arch;
+    mc->minimum_page_bits = qm->minimum_page_bits;
 }
 
 void qemu_register_machine(struct uc_struct *uc, QEMUMachine *m, const char *type_machine,

qemu/x86_64.h

@@ -2585,6 +2585,7 @@
 #define set_float_rounding_mode set_float_rounding_mode_x86_64
 #define set_flush_inputs_to_zero set_flush_inputs_to_zero_x86_64
 #define set_flush_to_zero set_flush_to_zero_x86_64
+#define set_preferred_target_page_bits set_preferred_target_page_bits_x86_64
 #define set_swi_errno set_swi_errno_x86_64
 #define sextract32 sextract32_x86_64
 #define sextract64 sextract64_x86_64