FAILED: patch "[PATCH] s390/entry: Scrub r12 register on kernel entry" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 0738d395aab8fae3b5a3ad3fc640630c91693c27
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026032923-rerun-crouch-f0cc@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0738d395aab8fae3b5a3ad3fc640630c91693c27 Mon Sep 17 00:00:00 2001
From: Vasily Gorbik <[email protected]>
Date: Thu, 26 Mar 2026 19:50:14 +0100
Subject: [PATCH] s390/entry: Scrub r12 register on kernel entry

Before commit f33f2d4c7c80 ("s390/bp: remove TIF_ISOLATE_BP"), all entry handlers loaded r12 with the current task pointer (lg %r12,__LC_CURRENT) for use by the BPENTER/BPEXIT macros. That commit removed TIF_ISOLATE_BP, dropping both the branch prediction macros and the r12 load, but did not add r12 to the register clearing sequence.

Add the missing xgr %r12,%r12 to make the register scrub consistent across all entry points.

index 4873fe9d891b..689d253e1afc 100644
@@ -271,6 +271,7 @@ SYM_CODE_START(system_call)
 	xgr	%r9,%r9
 	xgr	%r10,%r10
 	xgr	%r11,%r11
+	xgr	%r12,%r12
 	la	%r2,STACK_FRAME_OVERHEAD(%r15)	# pointer to pt_regs
 	mvc	__PT_R8(64,%r2),__LC_SAVE_AREA(%r13)
 	MBEAR	%r2,%r13

@@ -407,6 +408,7 @@ SYM_CODE_START(\name)
 	xgr	%r6,%r6
 	xgr	%r7,%r7
 	xgr	%r10,%r10
+	xgr	%r12,%r12
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA(%r13)
 	MBEAR	%r11,%r13

@@ -496,6 +498,7 @@ SYM_CODE_START(mcck_int_handler)
 	xgr	%r6,%r6
 	xgr	%r7,%r7
 	xgr	%r10,%r10
+	xgr	%r12,%r12
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
 	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)

Before commit f33f2d4c7c80 ("s390/bp: remove TIF_ISOLATE_BP"), all entry handlers loaded r12 with the current task pointer (lg %r12,__LC_CURRENT) for use by the BPENTER/BPEXIT macros. That commit removed TIF_ISOLATE_BP, dropping both the branch prediction macros and the r12 load, but did not add r12 to the register clearing sequence.

Add the missing xgr %r12,%r12 to make the register scrub consistent across all entry points.

---
 arch/s390/kernel/entry.S | 4 ++++
 1 file changed, 4 insertions(+)

index 0476ce7700df..b8c5c78b0d14 100644
@@ -300,6 +300,7 @@ SYM_CODE_START(system_call)
 	xgr	%r9,%r9
 	xgr	%r10,%r10
 	xgr	%r11,%r11
+	xgr	%r12,%r12
 	la	%r2,STACK_FRAME_OVERHEAD(%r15)	# pointer to pt_regs
 	mvc	__PT_R8(64,%r2),__LC_SAVE_AREA_SYNC
 	MBEAR	%r2

@@ -378,6 +379,7 @@ SYM_CODE_START(pgm_check_handler)
 	xgr	%r5,%r5
 	xgr	%r6,%r6
 	xgr	%r7,%r7
+	xgr	%r12,%r12
 	lgr	%r2,%r11
 	brasl	%r14,__do_pgm_check
 	tmhh	%r8,0x0001		# returning to user space?

@@ -439,6 +441,7 @@ SYM_CODE_START(\name)
 	xgr	%r6,%r6
 	xgr	%r7,%r7
 	xgr	%r10,%r10
+	xgr	%r12,%r12
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA_ASYNC
 	MBEAR	%r11

@@ -547,6 +550,7 @@ SYM_CODE_START(mcck_int_handler)
 	xgr	%r6,%r6
 	xgr	%r7,%r7
 	xgr	%r10,%r10
+	xgr	%r12,%r12
 	mvc	__PT_R8(64,%r11),0(%r14)
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)

2.53.0