powerpc: Provide a way to defer perf counter work until interrupts are enabled

Because 64-bit powerpc uses lazy (soft) interrupt disabling, it is
possible for a performance monitor exception to come in when the
kernel thinks interrupts are disabled (i.e. when they are
soft-disabled but hard-enabled).  In such a situation the performance
monitor exception handler might have some processing to do (such as
process wakeups) which can't be done in what is effectively an NMI
handler.

This provides a way to defer that work until interrupts get enabled,
either in raw_local_irq_restore() or by returning from an interrupt
handler to code that had interrupts enabled.  We have a per-processor
flag that indicates that there is work pending to do when interrupts
subsequently get re-enabled.  This flag is checked in the interrupt
return path and in raw_local_irq_restore(), and if it is set,
perf_counter_do_pending() is called to do the pending work.

Signed-off-by: Paul Mackerras <paulus@samba.org>

3 files changed, 20 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 661d07d2146b..cea462900119 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -127,6 +127,7 @@ int main(void)
         DEFINE(PACAKMSR, offsetof(struct paca_struct, kernel_msr));
         DEFINE(PACASOFTIRQEN, offsetof(struct paca_struct, soft_enabled));
         DEFINE(PACAHARDIRQEN, offsetof(struct paca_struct, hard_enabled));
+        DEFINE(PACAPERFPEND, offsetof(struct paca_struct, perf_counter_pending));
         DEFINE(PACASLBCACHE, offsetof(struct paca_struct, slb_cache));
         DEFINE(PACASLBCACHEPTR, offsetof(struct paca_struct, slb_cache_ptr));
         DEFINE(PACACONTEXTID, offsetof(struct paca_struct, context.id));
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 383ed6eb0085..f30b4e553c53 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -526,6 +526,15 @@ ALT_FW_FTR_SECTION_END_IFCLR(FW_FEATURE_ISERIES)
 2:
         TRACE_AND_RESTORE_IRQ(r5);
 
+#ifdef CONFIG_PERF_COUNTERS
+        /* check paca->perf_counter_pending if we're enabling ints */
+        lbz     r3,PACAPERFPEND(r13)
+        and.    r3,r3,r5
+        beq     27f
+        bl      .perf_counter_do_pending
+27:
+#endif /* CONFIG_PERF_COUNTERS */
+
         /* extract EE bit and use it to restore paca->hard_enabled */
         ld      r3,_MSR(r1)
         rldicl  r4,r3,49,63             /* r0 = (r3 >> 15) & 1 */
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index ac222d0ab12e..4efb886ea439 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -104,6 +104,13 @@ static inline notrace void set_soft_enabled(unsigned long enable)
         : : "r" (enable), "i" (offsetof(struct paca_struct, soft_enabled)));
 }
 
+#ifdef CONFIG_PERF_COUNTERS
+notrace void __weak perf_counter_do_pending(void)
+{
+        set_perf_counter_pending(0);
+}
+#endif
+
 notrace void raw_local_irq_restore(unsigned long en)
 {
         /*
@@ -135,6 +142,9 @@ notrace void raw_local_irq_restore(unsigned long en)
                         iseries_handle_interrupts();
         }
 
+        if (get_perf_counter_pending())
+                perf_counter_do_pending();
+
         /*
          * if (get_paca()->hard_enabled) return;
          * But again we need to take care that gcc gets hard_enabled directly