[PATCH] x86/mm: fix slow_virt_to_phys() for X86_PAE again

[PATCH] x86/mm: fix slow_virt_to_phys() for X86_PAE again

[Dexuan Cui]

"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@microsoft.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: gregkh@linuxfoundation.org
Cc: linux-mm@kvack.org
Cc: olaf@aepfle.de
Cc: apw@canonical.com
Cc: jasowang@redhat.com
Cc: stable@vger.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

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Re: [PATCH] x86/mm: fix slow_virt_to_phys() for X86_PAE again

[Toshi Kani]

On Thu, 2016-02-25 at 01:58 -0800, Dexuan Cui wrote:
> "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@microsoft.com>
> Cc: Toshi Kani <toshi.kani@hpe.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: K. Y. Srinivasan <kys@microsoft.com>
> Cc: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: gregkh@linuxfoundation.org
> Cc: linux-mm@kvack.org
> Cc: olaf@aepfle.de
> Cc: apw@canonical.com
> Cc: jasowang@redhat.com
> Cc: stable@vger.kernel.org

Thanks for the fix and adding the comment to explain the trick! A The change
looks good to me.

Reviewed-by: Toshi Kani <toshi.kani@hpe.com>

-Toshi

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