> On 09 December 2025 at 10:03 am, Christian Zigotzky <[email protected]>
> wrote:
>
> I bisected today.
>
> 1. git clone
> https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git -b
> powerpc-6.19-1 a
>
> 2. cd a
>
> 3. git log
>
> Output:
>
> commit 9b36c7fc5aa5f2c6e6eeb9f312fdfe61b4291c9f (HEAD, tag: powerpc-6.19-1,
> origin/next-test, origin/next)
>
> ...
>
> 4. git bisect start
>
> 5. git bisect good f850568efe3a7a9ec4df357cfad1f997f0058924
>
> Merge tag 'i2c-for-6.18-rc5'
>
> 6. git bisect bad 9b36c7fc5aa5f2c6e6eeb9f312fdfe61b4291c9f
>
> macintosh/via-pmu-backlight: Include <linux/fb.h> and <linux/of.h>
>
> 7. git bisect bad
>
> 8. git bisect bad
>
> 9. git bisect good
>
> 10. git bisect bad
>
> 11. git bisect good
>
> 2997876c4a1a5864baa13d7393c2b68cf5b51183 is the first bad commit
> commit 2997876c4a1a5864baa13d7393c2b68cf5b51183
> Author: Christophe Leroy <[email protected]>
> Date: Thu Sep 11 14:30:12 2025 +0200
>
> powerpc/32: Restore clearing of MSR[RI] at interrupt/syscall exit
>
> Commit 13799748b957 ("powerpc/64: use interrupt restart table to speed
> up return from interrupt") removed the inconditional clearing of
> MSR[RI] when returning from interrupt into kernel. But powerpc/32
> doesn't implement interrupt restart table hence still need MSR[RI]
> to be cleared.
>
> It could be added back in interrupt_exit_kernel_prepare() but it is
> easier and better to add it back in entry_32.S for following reasons:
> - Writing to MSR must be followed by a synchronising instruction
> - The smaller the non recoverable section is the better it is
>
> So add a macro called clr_ri and use it in the three places that play
> up with SRR0/SRR1. Use it just before another mtspr for synchronisation
> to avoid having to add an isync.
>
> Now that's done in entry_32.S, exit_must_hard_disable() can return
> false for non book3s/64, taking into account that BOOKE doesn't have
> MSR_RI.
>
> Also add back blacklisting syscall_exit_finish for kprobe. This was
> initially added by commit 7cdf44013885 ("powerpc/entry32: Blacklist
> syscall exit points for kprobe.") then lost with
> commit 6f76a01173cc ("powerpc/syscall: implement system call
> entry/exit logic in C for PPC32").
>
> Fixes: 6f76a01173cc ("powerpc/syscall: implement system call entry/exit
> logic in C for PPC32")
> Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up
> return from interrupt")
> Signed-off-by: Christophe Leroy <[email protected]>
> Signed-off-by: Madhavan Srinivasan <[email protected]>
> Link:
> https://patch.msgid.link/66d0ab070563ad460ed481328ab0887c27f21a2c.1757593807.git.christophe.le...@csgroup.eu
>
> arch/powerpc/kernel/entry_32.S | 18 +++++++++++++++++-
> arch/powerpc/kernel/interrupt.c | 2 +-
> 2 files changed, 18 insertions(+), 2 deletions(-)
>
> 12. git revert 2997876c4a1a5864baa13d7393c2b68cf5b51183
>
> After reverting the first bad commit, the kernel boots without any problems.
>
I created a patch for reverting the first bad commit.
After patching, the kernel boots without any problems.
diff -rupN a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
--- a/arch/powerpc/kernel/entry_32.S 2025-12-09 06:57:20.681347393 +0100
+++ b/arch/powerpc/kernel/entry_32.S 2025-12-09 10:24:37.357301725 +0100
@@ -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
@@ -180,7 +168,6 @@ syscall_exit_finish:
REST_GPR(0, r1)
REST_GPRS(3, 12, r1)
b 1b
-_ASM_NOKPROBE_SYMBOL(syscall_exit_finish)
#ifdef CONFIG_44x
.L44x_icache_flush:
@@ -237,11 +224,10 @@ fast_exception_return:
/* Clear the exception marker on the stack to avoid confusing
stacktrace */
li r10, 0
stw r10, 8(r11)
- clr_ri r10
+ REST_GPR(10, r11)
mtspr SPRN_SRR1,r9
mtspr SPRN_SRR0,r12
REST_GPR(9, r11)
- REST_GPR(10, r11)
REST_GPR(12, r11)
REST_GPR(11, r11)
rfi
@@ -270,7 +256,6 @@ 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 +298,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRE
cmpwi cr1,r3,0
lwz r11,_NIP(r1)
lwz r12,_MSR(r1)
- clr_ri r4
mtspr SPRN_SRR0,r11
mtspr SPRN_SRR1,r12
diff -rupN a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
--- a/arch/powerpc/kernel/interrupt.c 2025-12-09 06:57:20.717347165 +0100
+++ b/arch/powerpc/kernel/interrupt.c 2025-12-09 10:24:37.357301725 +0100
@@ -38,7 +38,7 @@ static inline bool exit_must_hard_disabl
#else
static inline bool exit_must_hard_disable(void)
{
- return false;
+ return true;
}
#endif
