[FSL P50x0] Xorg always restarts again and again after the the PowerPC updates 5.13-1

[Nicholas Piggin]

Excerpts from Christian Zigotzky's message of May 14, 2021 6:20 am:
> On 13 May 2021 at 07:00pm, Christophe Leroy wrote:
>>
>> Ah yes, I remember this problem.
>>
>> Can you select CONFIG_VIRT_CPU_ACCOUNTING_GEN in your configuration ?
>>
>> Otherwise, I can try to fix the branch.
>>
>> Christophe
> I selected this. After that it compiles.
> 
> 1. git bisect good - Xorg restarts again and again
>      Output: [f9aa0ac1e9e82b60401ad567bdabc30598325bc1] Revert 
> "powerpc/64e/interrupt: use new interrupt return"
> 2. git bisect good - Xorg restarts again and again
>      Output: [cd6d259a14704741bf0cd1dcadb84c0de22d7f77] Revert 
> "powerpc/64e/interrupt: always save nvgprs on interrupt"
> 3. git bisect bad - Xorg works
>      Output: [9bfa20ef2ae54d3b9088dfbcde4ef97062cf5ef2] Revert 
> "powerpc/interrupt: update common interrupt code for"
> 4. git bisect good - Xorg restarts again and again
>      Output:
> 
> cd6d259a14704741bf0cd1dcadb84c0de22d7f77 is the first bad commit
> commit cd6d259a14704741bf0cd1dcadb84c0de22d7f77
> Author: Christophe Leroy <christophe.leroy at csgroup.eu>
> Date:   Thu May 13 09:52:06 2021 +0000
> 
>      Revert "powerpc/64e/interrupt: always save nvgprs on interrupt"
> 
>      This reverts commit 4228b2c3d20e9f80b847f809c38e6cf82864fa50.
> 
> :040000 040000 156542c857ad72776b69bb67b2f244afeeb7abd3 
> 92ea86ed097fce16238b0c2f2b343473894e4e8e M    arch

Thank you both very much for chasing this down.

I think I see the problem, it's clobbering r14 and r15 for some 
interrupts. Something like this is required, I'll give it more
review and testing though.

Thanks,
Nick

---
diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index 7c3654b0d0f4..b91ef04f1ce2 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -535,6 +535,10 @@ __end_interrupts:
 				PROLOG_ADDITION_2REGS)
 	mfspr	r14,SPRN_DEAR
 	mfspr	r15,SPRN_ESR
+	std	r14,_DAR(r1)
+	std	r15,_DSISR(r1)
+	ld	r14,PACA_EXGEN+EX_R14(r13)
+	ld	r15,PACA_EXGEN+EX_R15(r13)
 	EXCEPTION_COMMON(0x300)
 	b	storage_fault_common
 
@@ -544,6 +548,10 @@ __end_interrupts:
 				PROLOG_ADDITION_2REGS)
 	li	r15,0
 	mr	r14,r10
+	std	r14,_DAR(r1)
+	std	r15,_DSISR(r1)
+	ld	r14,PACA_EXGEN+EX_R14(r13)
+	ld	r15,PACA_EXGEN+EX_R15(r13)
 	EXCEPTION_COMMON(0x400)
 	b	storage_fault_common
 
@@ -557,6 +565,10 @@ __end_interrupts:
 				PROLOG_ADDITION_2REGS)
 	mfspr	r14,SPRN_DEAR
 	mfspr	r15,SPRN_ESR
+	std	r14,_DAR(r1)
+	std	r15,_DSISR(r1)
+	ld	r14,PACA_EXGEN+EX_R14(r13)
+	ld	r15,PACA_EXGEN+EX_R15(r13)
 	EXCEPTION_COMMON(0x600)
 	b	alignment_more	/* no room, go out of line */
 
@@ -565,10 +577,10 @@ __end_interrupts:
 	NORMAL_EXCEPTION_PROLOG(0x700, BOOKE_INTERRUPT_PROGRAM,
 				PROLOG_ADDITION_1REG)
 	mfspr	r14,SPRN_ESR
-	EXCEPTION_COMMON(0x700)
 	std	r14,_DSISR(r1)
-	addi	r3,r1,STACK_FRAME_OVERHEAD
 	ld	r14,PACA_EXGEN+EX_R14(r13)
+	EXCEPTION_COMMON(0x700)
+	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	program_check_exception
 	REST_NVGPRS(r1)
 	b	interrupt_return
@@ -725,11 +737,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
 	 * normal exception
 	 */
 	mfspr	r14,SPRN_DBSR
-	EXCEPTION_COMMON_CRIT(0xd00)
 	std	r14,_DSISR(r1)
-	addi	r3,r1,STACK_FRAME_OVERHEAD
 	ld	r14,PACA_EXCRIT+EX_R14(r13)
 	ld	r15,PACA_EXCRIT+EX_R15(r13)
+	EXCEPTION_COMMON_CRIT(0xd00)
+	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	DebugException
 	REST_NVGPRS(r1)
 	b	interrupt_return
@@ -796,11 +808,11 @@ kernel_dbg_exc:
 	 * normal exception
 	 */
 	mfspr	r14,SPRN_DBSR
-	EXCEPTION_COMMON_DBG(0xd08)
 	std	r14,_DSISR(r1)
-	addi	r3,r1,STACK_FRAME_OVERHEAD
 	ld	r14,PACA_EXDBG+EX_R14(r13)
 	ld	r15,PACA_EXDBG+EX_R15(r13)
+	EXCEPTION_COMMON_DBG(0xd08)
+	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	DebugException
 	REST_NVGPRS(r1)
 	b	interrupt_return
@@ -931,11 +943,7 @@ masked_interrupt_book3e_0x2c0:
  * original values stashed away in the PACA
  */
 storage_fault_common:
-	std	r14,_DAR(r1)
-	std	r15,_DSISR(r1)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	ld	r14,PACA_EXGEN+EX_R14(r13)
-	ld	r15,PACA_EXGEN+EX_R15(r13)
 	bl	do_page_fault
 	b	interrupt_return
 
@@ -944,11 +952,7 @@ storage_fault_common:
  * continues here.
  */
 alignment_more:
-	std	r14,_DAR(r1)
-	std	r15,_DSISR(r1)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	ld	r14,PACA_EXGEN+EX_R14(r13)
-	ld	r15,PACA_EXGEN+EX_R15(r13)
 	bl	alignment_exception
 	REST_NVGPRS(r1)
 	b	interrupt_return