linux-kernel - [PATCH 5.6 139/177] parisc: Fix kernel panic in mem

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Message-Id: <20200601174059.973087668@linuxfoundation.org>
Date:   Mon,  1 Jun 2020 19:54:37 +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, Helge Deller <deller@....de>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.6 139/177] parisc: Fix kernel panic in mem_init()

From: Helge Deller <deller@....de>

[ Upstream commit bf71bc16e02162388808949b179d59d0b571b965 ]

The Debian kernel v5.6 triggers this kernel panic:

 Kernel panic - not syncing: Bad Address (null pointer deref?)
 Bad Address (null pointer deref?): Code=26 (Data memory access rights trap) at addr 0000000000000000
 CPU: 0 PID: 0 Comm: swapper Not tainted 5.6.0-2-parisc64 #1 Debian 5.6.14-1
  IAOQ[0]: mem_init+0xb0/0x150
  IAOQ[1]: mem_init+0xb4/0x150
  RP(r2): start_kernel+0x6c8/0x1190
 Backtrace:
  [<0000000040101ab4>] start_kernel+0x6c8/0x1190
  [<0000000040108574>] start_parisc+0x158/0x1b8

on a HP-PARISC rp3440 machine with this memory layout:
 Memory Ranges:
  0) Start 0x0000000000000000 End 0x000000003fffffff Size   1024 MB
  1) Start 0x0000004040000000 End 0x00000040ffdfffff Size   3070 MB

Fix the crash by avoiding virt_to_page() and similar functions in
mem_init() until the memory zones have been fully set up.

Signed-off-by: Helge Deller <deller@....de>
Cc: stable@...r.kernel.org # v5.0+
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/parisc/mm/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/parisc/mm/init.c b/arch/parisc/mm/init.c
index 5224fb38d766..01d7071b23f7 100644
--- a/arch/parisc/mm/init.c
+++ b/arch/parisc/mm/init.c
@@ -562,7 +562,7 @@ void __init mem_init(void)
 			> BITS_PER_LONG);
 
 	high_memory = __va((max_pfn << PAGE_SHIFT));
-	set_max_mapnr(page_to_pfn(virt_to_page(high_memory - 1)) + 1);
+	set_max_mapnr(max_low_pfn);
 	memblock_free_all();
 
 #ifdef CONFIG_PA11
-- 
2.25.1