linux-kernel - [RFC] ARC: mm: Restrict definition of pfn_valid() macro for CONFIG

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Message-Id: <1480433346-18054-1-git-send-email-yuriy.kolerov@synopsys.com>
Date:   Tue, 29 Nov 2016 18:29:06 +0300
From:   Yuriy Kolerov <yuriy.kolerov@...opsys.com>
To:     linux-snps-arc@...ts.infradead.org
Cc:     Vineet.Gupta1@...opsys.com, Alexey.Brodkin@...opsys.com,
        linux-kernel@...r.kernel.org,
        Yuriy Kolerov <yuriy.kolerov@...opsys.com>
Subject: [RFC] ARC: mm: Restrict definition of pfn_valid() macro for CONFIG_FLATMEM

Despite the fact that subtraction of unsigned integers is a defined
behaviour however such operations can lead to unexpected results. Thus
it is better to check both left and right boundaries to avoid potential
bugs as it done in the generic page.h.

Signed-off-by: Yuriy Kolerov <yuriy.kolerov@...opsys.com>
---
 arch/arc/include/asm/page.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/include/asm/page.h b/arch/arc/include/asm/page.h
index 296c342..81cfc6c7 100644
--- a/arch/arc/include/asm/page.h
+++ b/arch/arc/include/asm/page.h
@@ -88,7 +88,7 @@ typedef pte_t * pgtable_t;
 #define ARCH_PFN_OFFSET		virt_to_pfn(CONFIG_LINUX_LINK_BASE)
 
 #ifdef CONFIG_FLATMEM
-#define pfn_valid(pfn)		(((pfn) - ARCH_PFN_OFFSET) < max_mapnr)
+#define pfn_valid(pfn)		((pfn) >= ARCH_PFN_OFFSET && ((pfn) - ARCH_PFN_OFFSET) < max_mapnr)
 #endif
 
 /*
-- 
2.7.4