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, 11 insertions, 0 deletions

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 2f0d1b032a89..7e890065cf39 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -179,6 +179,10 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
         }
 #endif
 
+        /* We restore the interrupt state now */
+        if (!arch_irq_disabled_regs(regs))
+                local_irq_enable();
+
         if (in_atomic() || mm == NULL) {
                 if (!user_mode(regs))
                         return SIGSEGV;
@@ -213,6 +217,13 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
                         goto bad_area_nosemaphore;
 
                 down_read(&mm->mmap_sem);
+        } else {
+                /*
+                 * The above down_read_trylock() might have succeeded in
+                 * which case we'll have missed the might_sleep() from
+                 * down_read():
+                 */
+                might_sleep();
         }
 
         vma = find_vma(mm, address);