linux-kernel - [PATCH] x86/mm: fix slow_virt_to_phys() for X86

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Message-Id: <1456394292-9030-1-git-send-email-decui@microsoft.com>
Date:	Thu, 25 Feb 2016 01:58:12 -0800
From:	Dexuan Cui <decui@...rosoft.com>
To:	gregkh@...uxfoundation.org, toshi.kani@....com,
	akpm@...ux-foundation.org, tglx@...utronix.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	driverdev-devel@...uxdriverproject.org, jasowang@...hat.com
Cc:	olaf@...fle.de, apw@...onical.com, kys@...rosoft.com,
	haiyangz@...rosoft.com
Subject: [PATCH] x86/mm: fix slow_virt_to_phys() for X86_PAE again

"d1cd12108346: x86, pageattr: Prevent overflow in slow_virt_to_phys() for X86_PAE"
was unintentionally removed by the recent
"34437e67a672: x86/mm: Fix slow_virt_to_phys() to handle large PAT bit".

And, the variable 'phys_addr' was defined as "unsigned long" by mistake -- it should
be "phys_addr_t".

As a result, Hyper-V network driver in 32-PAE Linux guest can't work again.

Fixes: "commmit 34437e67a672: x86/mm: Fix slow_virt_to_phys() to handle large PAT bit"
Signed-off-by: Dexuan Cui <decui@...rosoft.com>
Cc: Toshi Kani <toshi.kani@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: K. Y. Srinivasan <kys@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: gregkh@...uxfoundation.org
Cc: linux-mm@...ck.org
Cc: olaf@...fle.de
Cc: apw@...onical.com
Cc: jasowang@...hat.com
Cc: stable@...r.kernel.org
---
 arch/x86/mm/pageattr.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 2440814..9cf96d8 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -419,24 +419,30 @@ pmd_t *lookup_pmd_address(unsigned long address)
 phys_addr_t slow_virt_to_phys(void *__virt_addr)
 {
 	unsigned long virt_addr = (unsigned long)__virt_addr;
-	unsigned long phys_addr, offset;
+	phys_addr_t phys_addr;
+	unsigned long offset;
 	enum pg_level level;
 	pte_t *pte;
 
 	pte = lookup_address(virt_addr, &level);
 	BUG_ON(!pte);
 
+	/*
+	 * pXX_pfn() returns unsigned long, which must be cast to phys_addr_t
+	 * before being left-shifted PAGE_SHIFT bits -- this trick is to
+	 * make 32-PAE kernel work correctly.
+	 */
 	switch (level) {
 	case PG_LEVEL_1G:
-		phys_addr = pud_pfn(*(pud_t *)pte) << PAGE_SHIFT;
+		phys_addr = (phys_addr_t)pud_pfn(*(pud_t *)pte) << PAGE_SHIFT;
 		offset = virt_addr & ~PUD_PAGE_MASK;
 		break;
 	case PG_LEVEL_2M:
-		phys_addr = pmd_pfn(*(pmd_t *)pte) << PAGE_SHIFT;
+		phys_addr = (phys_addr_t)pmd_pfn(*(pmd_t *)pte) << PAGE_SHIFT;
 		offset = virt_addr & ~PMD_PAGE_MASK;
 		break;
 	default:
-		phys_addr = pte_pfn(*pte) << PAGE_SHIFT;
+		phys_addr = (phys_addr_t)pte_pfn(*pte) << PAGE_SHIFT;
 		offset = virt_addr & ~PAGE_MASK;
 	}
 
-- 
1.9.1