linux-kernel - [PATCH] x86, pageattr: fix slow_virt_to_phys() for X86

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Message-Id: <1414580017-27444-1-git-send-email-decui@microsoft.com>
Date:	Wed, 29 Oct 2014 03:53:37 -0700
From:	Dexuan Cui <decui@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, x86@...nel.org, olaf@...fle.de,
	apw@...onical.com, jasowang@...hat.com, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, dave.hansen@...el.com,
	riel@...hat.com
Cc:	kys@...rosoft.com, haiyangz@...rosoft.com
Subject: [PATCH] x86, pageattr: fix slow_virt_to_phys() for X86_PAE

pte_pfn() returns a PFN of long (32 bits in 32-PAE), then
"long << PAGE_SHIFT" will overflow for PFNs above 4GB.

Due to this issue, some Linux 32-PAE distros, running as guests on Hyper-V,
with 5GB memory assigned, can't load the netvsc driver successfully and
hence the synthetic network device can't work (we can use the kernel parameter
mem=3000M to work around the issue).

Cc: K. Y. Srinivasan <kys@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Signed-off-by: Dexuan Cui <decui@...rosoft.com>
---
 arch/x86/mm/pageattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index ae242a7..36de293 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -409,7 +409,7 @@ phys_addr_t slow_virt_to_phys(void *__virt_addr)
 	psize = page_level_size(level);
 	pmask = page_level_mask(level);
 	offset = virt_addr & ~pmask;
-	phys_addr = pte_pfn(*pte) << PAGE_SHIFT;
+	phys_addr = (phys_addr_t)pte_pfn(*pte) << PAGE_SHIFT;
 	return (phys_addr | offset);
 }
 EXPORT_SYMBOL_GPL(slow_virt_to_phys);
-- 
1.9.1

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