powerpc: Replace __get_cpu_var uses

This still has not been merged and now powerpc is the only arch that does
not have this change. Sorry about missing linuxppc-dev before.

V2->V2
  - Fix up to work against 3.18-rc1

__get_cpu_var() is used for multiple purposes in the kernel source. One of
them is address calculation via the form &__get_cpu_var(x).  This calculates
the address for the instance of the percpu variable of the current processor
based on an offset.

Other use cases are for storing and retrieving data from the current
processors percpu area.  __get_cpu_var() can be used as an lvalue when
writing data or on the right side of an assignment.

__get_cpu_var() is defined as :

__get_cpu_var() always only does an address determination. However, store
and retrieve operations could use a segment prefix (or global register on
other platforms) to avoid the address calculation.

this_cpu_write() and this_cpu_read() can directly take an offset into a
percpu area and use optimized assembly code to read and write per cpu
variables.

This patch converts __get_cpu_var into either an explicit address
calculation using this_cpu_ptr() or into a use of this_cpu operations that
use the offset.  Thereby address calculations are avoided and less registers
are used when code is generated.

At the end of the patch set all uses of __get_cpu_var have been removed so
the macro is removed too.

The patch set includes passes over all arches as well. Once these operations
are used throughout then specialized macros can be defined in non -x86
arches as well in order to optimize per cpu access by f.e.  using a global
register that may be set to the per cpu base.

Transformations done to __get_cpu_var()

1. Determine the address of the percpu instance of the current processor.

	DEFINE_PER_CPU(int, y);
	int *x = &__get_cpu_var(y);

    Converts to

	int *x = this_cpu_ptr(&y);

2. Same as #1 but this time an array structure is involved.

	DEFINE_PER_CPU(int, y[20]);
	int *x = __get_cpu_var(y);

    Converts to

	int *x = this_cpu_ptr(y);

3. Retrieve the content of the current processors instance of a per cpu
variable.

	DEFINE_PER_CPU(int, y);
	int x = __get_cpu_var(y)

   Converts to

	int x = __this_cpu_read(y);

4. Retrieve the content of a percpu struct

	DEFINE_PER_CPU(struct mystruct, y);
	struct mystruct x = __get_cpu_var(y);

   Converts to

	memcpy(&x, this_cpu_ptr(&y), sizeof(x));

5. Assignment to a per cpu variable

	DEFINE_PER_CPU(int, y)
	__get_cpu_var(y) = x;

   Converts to

	__this_cpu_write(y, x);

6. Increment/Decrement etc of a per cpu variable

	DEFINE_PER_CPU(int, y);
	__get_cpu_var(y)++

   Converts to

	__this_cpu_inc(y)

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <paulus@samba.org>
Signed-off-by: Christoph Lameter <cl@linux.com>
[mpe: Fix build errors caused by set/or_softirq_pending(), and rework
      assignment in __set_breakpoint() to use memcpy().]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 12 insertions, 12 deletions

diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index a7fd4cb78b78..15c99b649b04 100644
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -73,8 +73,8 @@ void save_mce_event(struct pt_regs *regs, long handled,
 		    uint64_t nip, uint64_t addr)
 {
 	uint64_t srr1;
-	int index = __get_cpu_var(mce_nest_count)++;
-	struct machine_check_event *mce = &__get_cpu_var(mce_event[index]);
+	int index = __this_cpu_inc_return(mce_nest_count);
+	struct machine_check_event *mce = this_cpu_ptr(&mce_event[index]);
 
 	/*
 	 * Return if we don't have enough space to log mce event.
@@ -143,7 +143,7 @@ void save_mce_event(struct pt_regs *regs, long handled,
  */
 int get_mce_event(struct machine_check_event *mce, bool release)
 {
-	int index = __get_cpu_var(mce_nest_count) - 1;
+	int index = __this_cpu_read(mce_nest_count) - 1;
 	struct machine_check_event *mc_evt;
 	int ret = 0;
 
@@ -153,7 +153,7 @@ int get_mce_event(struct machine_check_event *mce, bool release)
 
 	/* Check if we have MCE info to process. */
 	if (index < MAX_MC_EVT) {
-		mc_evt = &__get_cpu_var(mce_event[index]);
+		mc_evt = this_cpu_ptr(&mce_event[index]);
 		/* Copy the event structure and release the original */
 		if (mce)
 			*mce = *mc_evt;
@@ -163,7 +163,7 @@ int get_mce_event(struct machine_check_event *mce, bool release)
 	}
 	/* Decrement the count to free the slot. */
 	if (release)
-		__get_cpu_var(mce_nest_count)--;
+		__this_cpu_dec(mce_nest_count);
 
 	return ret;
 }
@@ -184,13 +184,13 @@ void machine_check_queue_event(void)
 	if (!get_mce_event(&evt, MCE_EVENT_RELEASE))
 		return;
 
-	index = __get_cpu_var(mce_queue_count)++;
+	index = __this_cpu_inc_return(mce_queue_count);
 	/* If queue is full, just return for now. */
 	if (index >= MAX_MC_EVT) {
-		__get_cpu_var(mce_queue_count)--;
+		__this_cpu_dec(mce_queue_count);
 		return;
 	}
-	__get_cpu_var(mce_event_queue[index]) = evt;
+	memcpy(this_cpu_ptr(&mce_event_queue[index]), &evt, sizeof(evt));
 
 	/* Queue irq work to process this event later. */
 	irq_work_queue(&mce_event_process_work);
@@ -208,11 +208,11 @@ static void machine_check_process_queued_event(struct irq_work *work)
 	 * For now just print it to console.
 	 * TODO: log this error event to FSP or nvram.
 	 */
-	while (__get_cpu_var(mce_queue_count) > 0) {
-		index = __get_cpu_var(mce_queue_count) - 1;
+	while (__this_cpu_read(mce_queue_count) > 0) {
+		index = __this_cpu_read(mce_queue_count) - 1;
 		machine_check_print_event_info(
-				&__get_cpu_var(mce_event_queue[index]));
-		__get_cpu_var(mce_queue_count)--;
+				this_cpu_ptr(&mce_event_queue[index]));
+		__this_cpu_dec(mce_queue_count);
 	}
 }