powerpc: Call do_page_fault() with interrupts off

We currently turn interrupts back to their previous state before
calling do_page_fault(). This can be annoying when debugging as
a bad fault will potentially have lost some processor state before
getting into the debugger.

We also end up calling some generic code with interrupts enabled
such as notify_page_fault() with interrupts enabled, which could
be unexpected.

This changes our code to behave more like other architectures,
and make the assembly entry code call into do_page_faults() with
interrupts disabled. They are conditionally re-enabled from
within do_page_fault() in the same spot x86 does it.

While there, add the might_sleep() test in the case of a successful
trylock of the mmap semaphore, again like x86.

Also fix a bug in the existing assembly where r12 (_MSR) could get
clobbered by C calls (the DTL accounting in the exception common
macro and DISABLE_INTS) in some cases.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

v2. Add the r12 clobber fix

1 files changed, 17 insertions, 42 deletions

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 3af80e82830b..d8ff6d37fc4d 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -559,6 +559,8 @@ data_access_common:
         mfspr   r10,SPRN_DSISR
         stw     r10,PACA_EXGEN+EX_DSISR(r13)
         EXCEPTION_PROLOG_COMMON(0x300, PACA_EXGEN)
+        DISABLE_INTS
+        ld      r12,_MSR(r1)
         ld      r3,PACA_EXGEN+EX_DAR(r13)
         lwz     r4,PACA_EXGEN+EX_DSISR(r13)
         li      r5,0x300
@@ -573,6 +575,7 @@ h_data_storage_common:
         stw     r10,PACA_EXGEN+EX_DSISR(r13)
         EXCEPTION_PROLOG_COMMON(0xe00, PACA_EXGEN)
         bl      .save_nvgprs
+        DISABLE_INTS
         addi    r3,r1,STACK_FRAME_OVERHEAD
         bl      .unknown_exception
         b       .ret_from_except
@@ -581,6 +584,8 @@ h_data_storage_common:
         .globl instruction_access_common
 instruction_access_common:
         EXCEPTION_PROLOG_COMMON(0x400, PACA_EXGEN)
+        DISABLE_INTS
+        ld      r12,_MSR(r1)
         ld      r3,_NIP(r1)
         andis.  r4,r12,0x5820
         li      r5,0x400
@@ -884,24 +889,6 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_SLB)
         lwz     r0,TI_PREEMPT(r11)      /* If we're in an "NMI" */
         andis.  r0,r0,NMI_MASK@h        /* (i.e. an irq when soft-disabled) */
         bne     77f                     /* then don't call hash_page now */
-
-        /* We run with interrupts both soft and hard disabled */
-        DISABLE_INTS
-
-        /*
-         * Currently, trace_hardirqs_off() will be called by DISABLE_INTS
-         * and will clobber volatile registers when irq tracing is enabled
-         * so we need to reload them. It may be possible to be smarter here
-         * and move the irq tracing elsewhere but let's keep it simple for
-         * now
-         */
-#ifdef CONFIG_TRACE_IRQFLAGS
-        ld      r3,_DAR(r1)
-        ld      r4,_DSISR(r1)
-        ld      r5,_TRAP(r1)
-        ld      r12,_MSR(r1)
-        clrrdi  r5,r5,4
-#endif /* CONFIG_TRACE_IRQFLAGS */
         /*
          * We need to set the _PAGE_USER bit if MSR_PR is set or if we are
          * accessing a userspace segment (even from the kernel). We assume
@@ -931,36 +918,16 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_SLB)
         beq     fast_exc_return_irq     /* Return from exception on success */
 
         /* For a hash failure, we don't bother re-enabling interrupts */
-        ble-    12f
-
-        /*
-         * hash_page couldn't handle it, set soft interrupt enable back
-         * to what it was before the trap.  Note that .arch_local_irq_restore
-         * handles any interrupts pending at this point.
-         */
-        ld      r3,SOFTE(r1)
-        TRACE_AND_RESTORE_IRQ_PARTIAL(r3, 11f)
-        bl      .arch_local_irq_restore
-        b       11f
-
-/* We have a data breakpoint exception - handle it */
-handle_dabr_fault:
-        bl      .save_nvgprs
-        ld      r4,_DAR(r1)
-        ld      r5,_DSISR(r1)
-        addi    r3,r1,STACK_FRAME_OVERHEAD
-        bl      .do_dabr
-        b       .ret_from_except_lite
+        ble-    13f
 
 /* Here we have a page fault that hash_page can't handle. */
 handle_page_fault:
-        ENABLE_INTS
 11:     ld      r4,_DAR(r1)
         ld      r5,_DSISR(r1)
         addi    r3,r1,STACK_FRAME_OVERHEAD
         bl      .do_page_fault
         cmpdi   r3,0
-        beq+    13f
+        beq+    12f
         bl      .save_nvgprs
         mr      r5,r3
         addi    r3,r1,STACK_FRAME_OVERHEAD
@@ -968,12 +935,20 @@ handle_page_fault:
         bl      .bad_page_fault
         b       .ret_from_except
 
-13:     b       .ret_from_except_lite
+/* We have a data breakpoint exception - handle it */
+handle_dabr_fault:
+        bl      .save_nvgprs
+        ld      r4,_DAR(r1)
+        ld      r5,_DSISR(r1)
+        addi    r3,r1,STACK_FRAME_OVERHEAD
+        bl      .do_dabr
+12:     b       .ret_from_except_lite
+
 
 /* We have a page fault that hash_page could handle but HV refused
  * the PTE insertion
  */
-12:     bl      .save_nvgprs
+13:     bl      .save_nvgprs
         mr      r5,r3
         addi    r3,r1,STACK_FRAME_OVERHEAD
         ld      r4,_DAR(r1)