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cpu: Support a target CPU having a variable page size

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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>
This commit is contained in:
Peter Maydell 2016-10-24 16:26:49 +01:00
parent 66ec9f4939
commit 20bccb82ff
5 changed files with 80 additions and 0 deletions
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7
include/hw/boards.h
View file

@ -86,6 +86,12 @@ typedef struct {
* Returns a @HotpluggableCPUList, which describes CPUs objects which
* could be added with -device/device_add.
* Caller is responsible for freeing returned list.
* @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 >*/
@ -124,6 +130,7 @@ struct MachineClass {
ram_addr_t default_ram_size;
bool option_rom_has_mr;
bool rom_file_has_mr;
int minimum_page_bits;
HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
DeviceState *dev);