linux-kernel - Re: [PATCH v3 31/41] powerpc/32: Dismantle EXC_XFER

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Date:   Mon, 2 Aug 2021 17:19:23 +0200
From:   LEROY Christophe <christophe.leroy@...roup.eu>
To:     Finn Thain <fthain@...ux-m68k.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Nick Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Stan Johnson <userm57@...oo.com>
Subject: Re: [PATCH v3 31/41] powerpc/32: Dismantle EXC_XFER_STD/LITE/TEMPLATE



Le 01/08/2021 à 03:21, Finn Thain a écrit :
> On Sat, 31 Jul 2021, Christophe Leroy wrote:
> 
>>>
>>> Stan Johnson contacted me about a regression in mainline that he
>>> observed on his G3 Powerbooks. Using 'git bisect' we determined that
>>> this patch was the cause of the regression, i.e. commit 4c0104a83fc3
>>> ("powerpc/32: Dismantle EXC_XFER_STD/LITE/TEMPLATE").
>>>
>>> When testing 4c0104a83fc and all subsequent builds, various user
>>> processes were liable to segfault. Here is the console log that Stan
>>> provided:
>>
>> Hi, i will be able to look at that more in details next week, however I
>> have a few preliminary qurstions.
>>
>> Can you reliabily reproduce the problem with the said commit, and can
>> you reliabily run without problem with the parent commit ?
> 
> Yes and yes. (I already asked Stan to establish those things before I
> contacted the list.)

I think I found the problem with that commit. Can you retry with the 
following change:

diff --git a/arch/powerpc/kernel/head_book3s_32.S 
b/arch/powerpc/kernel/head_book3s_32.S
index 0a3d7d4a9ec4..a294103a91a1 100644
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S
@@ -299,7 +299,7 @@ ALT_MMU_FTR_SECTION_END_IFSET(MMU_FTR_HPTE_TABLE)
  	EXCEPTION_PROLOG_1
  	EXCEPTION_PROLOG_2 0x300 DataAccess handle_dar_dsisr=1
  	prepare_transfer_to_handler
-	lwz	r5, _DSISR(r11)
+	lwz	r5, _DSISR(r1)
  	andis.	r0, r5, DSISR_DABRMATCH@h
  	bne-	1f
  	bl	do_page_fault
---
Thanks
Christophe