Re: [PATCH] powerpc/32: Restore disabling of interrupts at interrupt/syscall exit

[Madhavan Srinivasan <maddy@linux.ibm.com>]

On 12/20/25 4:47 PM, Christian Zigotzky wrote:
> On 19/12/25 13:23, Christophe Leroy (CS GROUP) wrote:
>> Commit 2997876c4a1a ("powerpc/32: Restore clearing of MSR[RI] at
>> interrupt/syscall exit") delayed clearing of MSR[RI], but missed that
>> both MSR[RI] and MSR[EE] are cleared at the same time, so the commit
>> also delayed the disabling of interrupts, leading to unexpected
>> behaviour.
>>
>> To fix that, mostly revert the blamed commit and restore the clearing
>> of MSR[RI] in interrupt_exit_kernel_prepare() instead. For 8xx it
>> implies adding a synchronising instruction after the mtspr in order to
>> make sure no instruction counter interrupt (used for perf events) will
>> fire just after clearing MSR[RI].
>>
>> Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
>> Closes: 
>> https://lore.kernel.org/all/4d0bd05d-6158-1323-3509-744d3fbe8fc7@xenosoft.de/
>> Reported-by: Guenter Roeck <linux@roeck-us.net>
>> Closes: 
>> https://lore.kernel.org/all/6b05eb1c-fdef-44e0-91a7-8286825e68f1@roeck-us.net/
>> Fixes: 2997876c4a1a ("powerpc/32: Restore clearing of MSR[RI] at 
>> interrupt/syscall exit")
>> Signed-off-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
>> ---
>>   arch/powerpc/include/asm/hw_irq.h |  2 +-
>>   arch/powerpc/include/asm/reg.h    |  1 +
>>   arch/powerpc/kernel/entry_32.S    | 15 ---------------
>>   arch/powerpc/kernel/interrupt.c   |  5 ++++-
>>   4 files changed, 6 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/hw_irq.h 
>> b/arch/powerpc/include/asm/hw_irq.h
>> index 1078ba88efaf..9cd945f2acaf 100644
>> --- a/arch/powerpc/include/asm/hw_irq.h
>> +++ b/arch/powerpc/include/asm/hw_irq.h
>> @@ -90,7 +90,7 @@ static inline void __hard_EE_RI_disable(void)
>>       if (IS_ENABLED(CONFIG_BOOKE))
>>           wrtee(0);
>>       else if (IS_ENABLED(CONFIG_PPC_8xx))
>> -        wrtspr(SPRN_NRI);
>> +        wrtspr_sync(SPRN_NRI);
>>       else if (IS_ENABLED(CONFIG_PPC_BOOK3S_64))
>>           __mtmsrd(0, 1);
>>       else
>> diff --git a/arch/powerpc/include/asm/reg.h 
>> b/arch/powerpc/include/asm/reg.h
>> index 3fe186635432..3449dd2b577d 100644
>> --- a/arch/powerpc/include/asm/reg.h
>> +++ b/arch/powerpc/include/asm/reg.h
>> @@ -1400,6 +1400,7 @@ static inline void mtmsr_isync(unsigned long val)
>>                        : "r" ((unsigned long)(v)) \
>>                        : "memory")
>>   #define wrtspr(rn)    asm volatile("mtspr " __stringify(rn) ",2" : 
>> : : "memory")
>> +#define wrtspr_sync(rn)    asm volatile("mtspr " __stringify(rn) 
>> ",2; sync" : : : "memory")
>>     static inline void wrtee(unsigned long val)
>>   {
>> diff --git a/arch/powerpc/kernel/entry_32.S 
>> b/arch/powerpc/kernel/entry_32.S
>> index 16f8ee6cb2cd..d8426251b1cd 100644
>> --- a/arch/powerpc/kernel/entry_32.S
>> +++ b/arch/powerpc/kernel/entry_32.S
>> @@ -101,17 +101,6 @@ SYM_FUNC_END(__kuep_unlock)
>>   .endm
>>   #endif
>>   -.macro    clr_ri trash
>> -#ifndef CONFIG_BOOKE
>> -#ifdef CONFIG_PPC_8xx
>> -    mtspr   SPRN_NRI, \trash
>> -#else
>> -    li    \trash, MSR_KERNEL & ~MSR_RI
>> -    mtmsr    \trash
>> -#endif
>> -#endif
>> -.endm
>> -
>>       .globl    transfer_to_syscall
>>   transfer_to_syscall:
>>       stw    r3, ORIG_GPR3(r1)
>> @@ -160,7 +149,6 @@ ret_from_syscall:
>>       cmpwi    r3,0
>>       REST_GPR(3, r1)
>>   syscall_exit_finish:
>> -    clr_ri    r4
>>       mtspr    SPRN_SRR0,r7
>>       mtspr    SPRN_SRR1,r8
>>   @@ -237,7 +225,6 @@ fast_exception_return:
>>       /* Clear the exception marker on the stack to avoid confusing 
>> stacktrace */
>>       li    r10, 0
>>       stw    r10, 8(r11)
>> -    clr_ri    r10
>>       mtspr    SPRN_SRR1,r9
>>       mtspr    SPRN_SRR0,r12
>>       REST_GPR(9, r11)
>> @@ -270,7 +257,6 @@ interrupt_return:
>>   .Lfast_user_interrupt_return:
>>       lwz    r11,_NIP(r1)
>>       lwz    r12,_MSR(r1)
>> -    clr_ri    r4
>>       mtspr    SPRN_SRR0,r11
>>       mtspr    SPRN_SRR1,r12
>>   @@ -313,7 +299,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
>>       cmpwi    cr1,r3,0
>>       lwz    r11,_NIP(r1)
>>       lwz    r12,_MSR(r1)
>> -    clr_ri    r4
>>       mtspr    SPRN_SRR0,r11
>>       mtspr    SPRN_SRR1,r12
>>   diff --git a/arch/powerpc/kernel/interrupt.c 
>> b/arch/powerpc/kernel/interrupt.c
>> index aea6f7e8e9c6..e63bfde13e03 100644
>> --- a/arch/powerpc/kernel/interrupt.c
>> +++ b/arch/powerpc/kernel/interrupt.c
>> @@ -38,7 +38,7 @@ static inline bool exit_must_hard_disable(void)
>>   #else
>>   static inline bool exit_must_hard_disable(void)
>>   {
>> -    return false;
>> +    return true;
>>   }
>>   #endif
>>   @@ -443,6 +443,9 @@ notrace unsigned long 
>> interrupt_exit_kernel_prepare(struct pt_regs *regs)
>>             if (unlikely(stack_store))
>>               __hard_EE_RI_disable();
>> +#else
>> +    } else {
>> +        __hard_EE_RI_disable();
>>   #endif /* CONFIG_PPC64 */
>>       }
>
> The patched kernel 6.19.0-rc1 boots without any problems. Thank you.
>
> Tested-by Christian Zigotzky <chzigotzky@xenosoft.de>


Thanks for testing, Will pull this as part of rc fixes
Maddy