[tip:x86/urgent] x86, pageattr: Prevent overflow in slow_virt_to_phys() for X86_PAE

[tip-bot for Dexuan Cui]

Commit-ID:  d1cd1210834649ce1ca6bafe5ac25d2f40331343
Gitweb:     http://git.kernel.org/tip/d1cd1210834649ce1ca6bafe5ac25d2f40331343
Author:     Dexuan Cui <decui@xxxxxxxxxxxxx>
AuthorDate: Wed, 29 Oct 2014 03:53:37 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 29 Oct 2014 10:57:21 +0100

x86, pageattr: Prevent overflow in slow_virt_to_phys() for X86_PAE

pte_pfn() returns a PFN of long (32 bits in 32-PAE), so "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).

Cast pte_pfn() to phys_addr_t before shifting.

Fixes: "commit d76565344512: x86, mm: Create slow_virt_to_phys()"
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: gregkh@xxxxxxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: olaf@xxxxxxxxx
Cc: apw@xxxxxxxxxxxxx
Cc: jasowang@xxxxxxxxxx
Cc: dave.hansen@xxxxxxxxx
Cc: riel@xxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1414580017-27444-1-git-send-email-decui@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 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);
--
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