[PATCH] powerpc/32s: Fix RTAS machine check with VMAP stack

When we have VMAP stack, exception prolog 1 sets r1, not r11.

Fixes: da7bb43ab9da ("powerpc/32: Fix vmap stack - Properly set r1 before activating MMU")
Fixes: d2e006036082 ("powerpc/32: Use SPRN_SPRG_SCRATCH2 in exception prologs")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/kernel/head_book3s_32.S | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
index 349bf3f0c3af..fbc48a500846 100644
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S

@@ -260,9 +260,16 @@ __secondary_hold_acknowledge:
 MachineCheck:
 	EXCEPTION_PROLOG_0
 #ifdef CONFIG_PPC_CHRP
+#ifdef CONFIG_VMAP_STACK
+	mtspr	SPRN_SPRG_SCRATCH2,r1
+	mfspr	r1, SPRN_SPRG_THREAD
+	lwz	r1, RTAS_SP(r1)
+	cmpwi	cr1, r1, 0
+#else
 	mfspr	r11, SPRN_SPRG_THREAD
 	lwz	r11, RTAS_SP(r11)
 	cmpwi	cr1, r11, 0
+#endif
 	bne	cr1, 7f
 #endif /* CONFIG_PPC_CHRP */
 	EXCEPTION_PROLOG_1 for_rtas=1

-- 
2.25.0

On Tue, 22 Dec 2020 07:11:18 +0000 (UTC), Christophe Leroy wrote:

When we have VMAP stack, exception prolog 1 sets r1, not r11.

Applied to powerpc/fixes.

[1/1] powerpc/32s: Fix RTAS machine check with VMAP stack
      https://git.kernel.org/powerpc/c/9c7422b92cb27369653c371ad9c44a502e5eea8f

cheers

Le 22/12/2020 à 08:11, Christophe Leroy a écrit :

When we have VMAP stack, exception prolog 1 sets r1, not r11.

But exception prolog 1 uses r1 to setup r1 when machine check happens in kernel.
So r1 must be restored when the branch is not taken. See subsequent patch I just sent out.

Christophe

Christophe Leroy [off-list ref] writes:

Le 22/12/2020 à 08:11, Christophe Leroy a écrit :

quoted

When we have VMAP stack, exception prolog 1 sets r1, not r11.

But exception prolog 1 uses r1 to setup r1 when machine check happens in kernel.
So r1 must be restored when the branch is not taken. See subsequent patch I just sent out.

OK. This is still on the tip of fixes, so I'll rewind it to drop this
commit, and then apply this and the fixup as one patch next week.

cheers