linux-kernel - [PATCH v2] ARM: memblock limit must be pmd-aligned

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Message-Id: <20170627173330.13804-1-opendmb@gmail.com>
Date:   Tue, 27 Jun 2017 10:33:29 -0700
From:   Doug Berger <opendmb@...il.com>
To:     Russell King <linux@...linux.org.uk>
Cc:     Doug Berger <opendmb@...il.com>, Laura Abbott <labbott@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Jon Medhurst <tixy@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Marc Zyngier <marc.zyngier@....com>,
        linux-arm-kernel@...ts.infradead.org (moderated list:ARM PORT),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2] ARM: memblock limit must be pmd-aligned

The pmd containing memblock_limit is cleared by prepare_page_table()
which creates the opportunity for early_alloc() to allocate unmapped
memory if memblock_limit is not pmd aligned causing a boot-time hang.

Commit 965278dcb8ab ("ARM: 8356/1: mm: handle non-pmd-aligned end of RAM")
attempted to resolve this problem, but there is a path through the
adjust_lowmem_bounds() routine where if all memory regions start and
end on pmd-aligned addresses the memblock_limit will be set to
arm_lowmem_limit.

Since arm_lowmem_limit can be affected by the vmalloc early parameter,
the value of arm_lowmem_limit may not be pmd-aligned. This commit
corrects this oversight such that memblock_limit is always rounded
down to pmd-alignment.

Fixes: 965278dcb8ab ("ARM: 8356/1: mm: handle non-pmd-aligned end of RAM")
Signed-off-by: Doug Berger <opendmb@...il.com>
Suggested-by: Mark Rutland <mark.rutland@....com>
---
Changes for v2:
 - Cleaner equivalent implementation suggested by Mark Rutland
 - Revised description to better capture the history

 arch/arm/mm/mmu.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 31af3cb59a60..e46a6a446cdd 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1218,15 +1218,15 @@ void __init adjust_lowmem_bounds(void)
 
 	high_memory = __va(arm_lowmem_limit - 1) + 1;
 
+	if (!memblock_limit)
+		memblock_limit = arm_lowmem_limit;
+
 	/*
 	 * Round the memblock limit down to a pmd size.  This
 	 * helps to ensure that we will allocate memory from the
 	 * last full pmd, which should be mapped.
 	 */
-	if (memblock_limit)
-		memblock_limit = round_down(memblock_limit, PMD_SIZE);
-	if (!memblock_limit)
-		memblock_limit = arm_lowmem_limit;
+	memblock_limit = round_down(memblock_limit, PMD_SIZE);
 
 	if (!IS_ENABLED(CONFIG_HIGHMEM) || cache_is_vipt_aliasing()) {
 		if (memblock_end_of_DRAM() > arm_lowmem_limit) {
-- 
2.13.0