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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
Download patch file Download diff file Expand all files Collapse all files

9
include/exec/cpu-all.h
View file

@ -189,6 +189,15 @@ void address_space_stq(AddressSpace *as, hwaddr addr, uint64_t val,
/* page related stuff */
#ifdef TARGET_PAGE_BITS_VARY
extern bool target_page_bits_decided;
extern int target_page_bits;
#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)

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);

12
include/qemu-common.h
View file

@ -81,6 +81,18 @@ bool tcg_enabled(void);
void cpu_exec_init_all(void);
/**
* 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(int bits);
/**
* Sends a (part of) iovec down a socket, yielding when the socket is full, or
* Receives data into a (part of) iovec from a socket,