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[Qemu-devel] [PATCH v3 4/7] cpu: Support a target CPU having a variable
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [PATCH v3 4/7] cpu: Support a target CPU having a variable page size |
Date: |
Tue, 11 Oct 2016 18:08:16 +0100 |
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 <address@hidden>
---
exec.c | 42 ++++++++++++++++++++++++++++++++++++++++++
include/exec/cpu-all.h | 9 +++++++++
include/hw/boards.h | 7 +++++++
include/qemu-common.h | 12 ++++++++++++
vl.c | 10 ++++++++++
5 files changed, 80 insertions(+)
diff --git a/exec.c b/exec.c
index 86b09ac..25d972f 100644
--- a/exec.c
+++ b/exec.c
@@ -93,6 +93,11 @@ static MemoryRegion io_mem_unassigned;
#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 @@ __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.
+ */
+#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 {
@@ -2797,6 +2831,14 @@ void cpu_register_map_client(QEMUBH *bh)
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);
diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index b6a7059..861260d 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -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)
diff --git a/include/hw/boards.h b/include/hw/boards.h
index e46a744..a51da9c 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -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);
diff --git a/include/qemu-common.h b/include/qemu-common.h
index 9e8b0bd..7e6e4fe 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -82,6 +82,18 @@ 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,
* yielding when there is no data in the socket.
diff --git a/vl.c b/vl.c
index eb3c5ee..5feaae9 100644
--- a/vl.c
+++ b/vl.c
@@ -4088,6 +4088,16 @@ int main(int argc, char **argv, char **envp)
}
object_property_add_child(object_get_root(), "machine",
OBJECT(current_machine), &error_abort);
+
+ if (machine_class->minimum_page_bits) {
+ if (!set_preferred_target_page_bits(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();
+ }
+ }
+
cpu_exec_init_all();
if (machine_class->hw_version) {
--
2.7.4
- [Qemu-devel] [PATCH v3 0/7] Runtime pagesize computation, Peter Maydell, 2016/10/11
- [Qemu-devel] [PATCH v3 5/7] migration/savevm.c: migrate non-default page size, Peter Maydell, 2016/10/11
- [Qemu-devel] [PATCH v3 1/7] migration: Remove static allocation of xzblre cache buffer, Peter Maydell, 2016/10/11
- [Qemu-devel] [PATCH v3 4/7] cpu: Support a target CPU having a variable page size,
Peter Maydell <=
- [Qemu-devel] [PATCH v3 2/7] exec.c: Remove static allocation of sub_section of sub_page, Peter Maydell, 2016/10/11
- Re: [Qemu-devel] [Qemu-arm] [PATCH v3 0/7] Runtime pagesize computation, Peter Maydell, 2016/10/11
- Re: [Qemu-devel] [PATCH v3 0/7] Runtime pagesize computation, Richard Henderson, 2016/10/11
- Re: [Qemu-devel] [PATCH v3 0/7] Runtime pagesize computation, no-reply, 2016/10/11
- Re: [Qemu-devel] [Qemu-arm] [PATCH v3 0/7] Runtime pagesize computation, Peter Maydell, 2016/10/21