linux-kernel - [PATCH 5.15 215/277] highmem: fix checks in __kmap_local_sched

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Message-Id: <20220412062948.262393978@linuxfoundation.org>
Date:   Tue, 12 Apr 2022 08:30:18 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Max Filippov <jcmvbkbc@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.15 215/277] highmem: fix checks in __kmap_local_sched_{in,out}

From: Max Filippov <jcmvbkbc@...il.com>

commit 66f133ceab7456c789f70a242991ed1b27ba1c3d upstream.

When CONFIG_DEBUG_KMAP_LOCAL is enabled __kmap_local_sched_{in,out} check
that even slots in the tsk->kmap_ctrl.pteval are unmapped.  The slots are
initialized with 0 value, but the check is done with pte_none.  0 pte
however does not necessarily mean that pte_none will return true.  e.g.
on xtensa it returns false, resulting in the following runtime warnings:

 WARNING: CPU: 0 PID: 101 at mm/highmem.c:627 __kmap_local_sched_out+0x51/0x108
 CPU: 0 PID: 101 Comm: touch Not tainted 5.17.0-rc7-00010-gd3a1cdde80d2-dirty #13
 Call Trace:
   dump_stack+0xc/0x40
   __warn+0x8f/0x174
   warn_slowpath_fmt+0x48/0xac
   __kmap_local_sched_out+0x51/0x108
   __schedule+0x71a/0x9c4
   preempt_schedule_irq+0xa0/0xe0
   common_exception_return+0x5c/0x93
   do_wp_page+0x30e/0x330
   handle_mm_fault+0xa70/0xc3c
   do_page_fault+0x1d8/0x3c4
   common_exception+0x7f/0x7f

 WARNING: CPU: 0 PID: 101 at mm/highmem.c:664 __kmap_local_sched_in+0x50/0xe0
 CPU: 0 PID: 101 Comm: touch Tainted: G        W         5.17.0-rc7-00010-gd3a1cdde80d2-dirty #13
 Call Trace:
   dump_stack+0xc/0x40
   __warn+0x8f/0x174
   warn_slowpath_fmt+0x48/0xac
   __kmap_local_sched_in+0x50/0xe0
   finish_task_switch$isra$0+0x1ce/0x2f8
   __schedule+0x86e/0x9c4
   preempt_schedule_irq+0xa0/0xe0
   common_exception_return+0x5c/0x93
   do_wp_page+0x30e/0x330
   handle_mm_fault+0xa70/0xc3c
   do_page_fault+0x1d8/0x3c4
   common_exception+0x7f/0x7f

Fix it by replacing !pte_none(pteval) with pte_val(pteval) != 0.

Link: https://lkml.kernel.org/r/20220403235159.3498065-1-jcmvbkbc@gmail.com
Fixes: 5fbda3ecd14a ("sched: highmem: Store local kmaps in task struct")
Signed-off-by: Max Filippov <jcmvbkbc@...il.com>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/highmem.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -627,7 +627,7 @@ void __kmap_local_sched_out(void)
 
 		/* With debug all even slots are unmapped and act as guard */
 		if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL) && !(i & 0x01)) {
-			WARN_ON_ONCE(!pte_none(pteval));
+			WARN_ON_ONCE(pte_val(pteval) != 0);
 			continue;
 		}
 		if (WARN_ON_ONCE(pte_none(pteval)))
@@ -664,7 +664,7 @@ void __kmap_local_sched_in(void)
 
 		/* With debug all even slots are unmapped and act as guard */
 		if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL) && !(i & 0x01)) {
-			WARN_ON_ONCE(!pte_none(pteval));
+			WARN_ON_ONCE(pte_val(pteval) != 0);
 			continue;
 		}
 		if (WARN_ON_ONCE(pte_none(pteval)))