powerpc: Allow perf_counters to access user memory at interrupt time
This provides a mechanism to allow the perf_counters code to access
user memory in a PMU interrupt routine. Such an access can cause
various kinds of interrupt: SLB miss, MMU hash table miss, segment
table miss, or TLB miss, depending on the processor. This commit
only deals with 64-bit classic/server processors, which use an MMU
hash table. 32-bit processors are already able to access user memory
at interrupt time. Since we don't soft-disable on 32-bit, we avoid
the possibility of reentering hash_page or the TLB miss handlers,
since they run with interrupts disabled.
On 64-bit processors, an SLB miss interrupt on a user address will
update the slb_cache and slb_cache_ptr fields in the paca. This is
OK except in the case where a PMU interrupt occurs in switch_slb,
which also accesses those fields. To prevent this, we hard-disable
interrupts in switch_slb. Interrupts are already soft-disabled at
this point, and will get hard-enabled when they get soft-enabled
later.
This also reworks slb_flush_and_rebolt: to avoid hard-disabling twice,
and to make sure that it clears the slb_cache_ptr when called from
other callers than switch_slb, the existing routine is renamed to
__slb_flush_and_rebolt, which is called by switch_slb and the new
version of slb_flush_and_rebolt.
Similarly, switch_stab (used on POWER3 and RS64 processors) gets a
hard_irq_disable() to protect the per-cpu variables used there and
in ste_allocate.
If a MMU hashtable miss interrupt occurs, normally we would call
hash_page to look up the Linux PTE for the address and create a HPTE.
However, hash_page is fairly complex and takes some locks, so to
avoid the possibility of deadlock, we check the preemption count
to see if we are in a (pseudo-)NMI handler, and if so, we don't call
hash_page but instead treat it like a bad access that will get
reported up through the exception table mechanism. An interrupt
whose handler runs even though the interrupt occurred when
soft-disabled (such as the PMU interrupt) is considered a pseudo-NMI
handler, which should use nmi_enter()/nmi_exit() rather than
irq_enter()/irq_exit().
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
index 5b7038f..a685652 100644
--- a/arch/powerpc/mm/slb.c
+++ b/arch/powerpc/mm/slb.c
@@ -92,15 +92,13 @@
: "memory" );
}
-void slb_flush_and_rebolt(void)
+static void __slb_flush_and_rebolt(void)
{
/* If you change this make sure you change SLB_NUM_BOLTED
* appropriately too. */
unsigned long linear_llp, vmalloc_llp, lflags, vflags;
unsigned long ksp_esid_data, ksp_vsid_data;
- WARN_ON(!irqs_disabled());
-
linear_llp = mmu_psize_defs[mmu_linear_psize].sllp;
vmalloc_llp = mmu_psize_defs[mmu_vmalloc_psize].sllp;
lflags = SLB_VSID_KERNEL | linear_llp;
@@ -117,12 +115,6 @@
ksp_vsid_data = get_slb_shadow()->save_area[2].vsid;
}
- /*
- * We can't take a PMU exception in the following code, so hard
- * disable interrupts.
- */
- hard_irq_disable();
-
/* We need to do this all in asm, so we're sure we don't touch
* the stack between the slbia and rebolting it. */
asm volatile("isync\n"
@@ -139,6 +131,21 @@
: "memory");
}
+void slb_flush_and_rebolt(void)
+{
+
+ WARN_ON(!irqs_disabled());
+
+ /*
+ * We can't take a PMU exception in the following code, so hard
+ * disable interrupts.
+ */
+ hard_irq_disable();
+
+ __slb_flush_and_rebolt();
+ get_paca()->slb_cache_ptr = 0;
+}
+
void slb_vmalloc_update(void)
{
unsigned long vflags;
@@ -180,12 +187,20 @@
/* Flush all user entries from the segment table of the current processor. */
void switch_slb(struct task_struct *tsk, struct mm_struct *mm)
{
- unsigned long offset = get_paca()->slb_cache_ptr;
+ unsigned long offset;
unsigned long slbie_data = 0;
unsigned long pc = KSTK_EIP(tsk);
unsigned long stack = KSTK_ESP(tsk);
unsigned long unmapped_base;
+ /*
+ * We need interrupts hard-disabled here, not just soft-disabled,
+ * so that a PMU interrupt can't occur, which might try to access
+ * user memory (to get a stack trace) and possible cause an SLB miss
+ * which would update the slb_cache/slb_cache_ptr fields in the PACA.
+ */
+ hard_irq_disable();
+ offset = get_paca()->slb_cache_ptr;
if (!cpu_has_feature(CPU_FTR_NO_SLBIE_B) &&
offset <= SLB_CACHE_ENTRIES) {
int i;
@@ -200,7 +215,7 @@
}
asm volatile("isync" : : : "memory");
} else {
- slb_flush_and_rebolt();
+ __slb_flush_and_rebolt();
}
/* Workaround POWER5 < DD2.1 issue */