On 2017/06/16 03:16PM, Michael Ellerman wrote:

"Naveen N. Rao" [off-list ref] writes:

quoted

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index ae418b85c17c..17ee701b8336 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S

@@ -1442,7 +1440,9 @@ do_hash_page:
 
 /* Here we have a page fault that hash_page can't handle. */
 handle_page_fault:
-11:	ld	r4,_DAR(r1)
+	andis.  r0,r4,DSISR_DABRMATCH@h
+	bne-    handle_dabr_fault

This broke hash. Please test hash! :)

Gah! :double-face-palm:
I don't know how I missed this... (yes, I do)

As always, thanks Michael!

I think we can optimize this a bit more to eliminate the loads in
handle_page_fault. Here's an incremental patch above your changes for
-next, this time boot-tested with radix and disable_radix.

- Naveen

-----
[PATCH] powerpc64/exceptions64s: Eliminate a few un-necessary memory loads

In do_hash_page(), we re-load DSISR from stack though it is still present
in register r4. Eliminate the memory load by preserving this register.

Furthermore, handler_page_fault() reloads DAR and DSISR from memory and
this is only required if we fall through from do_hash_page().
Otherwise, r3 and r4 already have DAR and DSISR loaded. Re-use those
and have do_hash_page() reload those registers when falling-through.

Signed-off-by: Naveen N. Rao <redacted>
---
 arch/powerpc/kernel/exceptions-64s.S | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index dd619faab862..b5182a1ef3d6 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S

@@ -1426,8 +1426,8 @@ do_hash_page:
 	 *
 	 * at return r3 = 0 for success, 1 for page fault, negative for error
 	 */
+	mr	r6,r4
         mr 	r4,r12
-	ld      r6,_DSISR(r1)
 	bl	__hash_page		/* build HPTE if possible */
         cmpdi	r3,0			/* see if __hash_page succeeded */
 

@@ -1437,7 +1437,8 @@ do_hash_page:
 	/* Error */
 	blt-	13f
 
-	/* Reload DSISR into r4 for the DABR check below */
+	/* Reload DAR/DSISR for handle_page_fault */
+	ld	r3,_DAR(r1)
 	ld      r4,_DSISR(r1)
 #endif /* CONFIG_PPC_STD_MMU_64 */
 

@@ -1445,8 +1446,8 @@ do_hash_page:
 handle_page_fault:
 	andis.  r0,r4,DSISR_DABRMATCH@h
 	bne-    handle_dabr_fault
-	ld	r4,_DAR(r1)
-	ld	r5,_DSISR(r1)
+	mr	r5,r4
+	mr	r4,r3
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	do_page_fault
 	cmpdi	r3,0

-- 
2.13.1