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[PATCH v2 3/8] arm/xen: implement correctly pfn_to_mfn

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  [PATCH v2 3/8] arm/xen: implement correctly pfn_to_mfn Julien Grall <julien.grall@citrix.com> - 2015-08-04 20:20 +0200
    Re: [PATCH v2 3/8] arm/xen: implement correctly pfn_to_mfn Stefano Stabellini <stefano.stabellini@eu.citrix.com> - 2015-08-05 12:00 +0200

#1200207 — [PATCH v2 3/8] arm/xen: implement correctly pfn_to_mfn

After the commit introducing convertion between DMA and guest address,
all the callers of pfn_to_mfn are expecting to get a GFN (Guest Frame
Number). On ARM, all the guests are auto-translated so the GFN is equal
to the Linux PFN (Pseudo-physical Frame Number).

The current implementation may return an MFN if the caller is passing a
PFN associated to a mapped foreign grant. In pratical, I haven't seen
the problem on running guest but we should fix it for the sake of
correctness.

Correct the implementation by always returning the pfn passed in parameter.

A follow-up patch will take care to rename pfn_to_mfn to a suitable
name.

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
---
 arch/arm/include/asm/xen/page.h | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/arch/arm/include/asm/xen/page.h b/arch/arm/include/asm/xen/page.h
index bc5e77c..087d86e 100644
--- a/arch/arm/include/asm/xen/page.h
+++ b/arch/arm/include/asm/xen/page.h
@@ -36,14 +36,6 @@ extern struct rb_root phys_to_mach;
 
 static inline unsigned long pfn_to_mfn(unsigned long pfn)
 {
-	unsigned long mfn;
-
-	if (phys_to_mach.rb_node != NULL) {
-		mfn = __pfn_to_mfn(pfn);
-		if (mfn != INVALID_P2M_ENTRY)
-			return mfn;
-	}
-
 	return pfn;
 }
 
-- 
2.1.4

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#1200604

On Tue, 4 Aug 2015, Julien Grall wrote:
> After the commit introducing convertion between DMA and guest address,
                                                                  ^ addresses

> all the callers of pfn_to_mfn are expecting to get a GFN (Guest Frame
> Number). On ARM, all the guests are auto-translated so the GFN is equal
> to the Linux PFN (Pseudo-physical Frame Number).
> 
> The current implementation may return an MFN if the caller is passing a
> PFN associated to a mapped foreign grant. In pratical, I haven't seen
                                               ^ practice


> the problem on running guest but we should fix it for the sake of
> correctness.
> 
> Correct the implementation by always returning the pfn passed in parameter.
> 
> A follow-up patch will take care to rename pfn_to_mfn to a suitable
> name.
> 
> Signed-off-by: Julien Grall <julien.grall@citrix.com>
> Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: linux-arm-kernel@lists.infradead.org

Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>


>  arch/arm/include/asm/xen/page.h | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/arch/arm/include/asm/xen/page.h b/arch/arm/include/asm/xen/page.h
> index bc5e77c..087d86e 100644
> --- a/arch/arm/include/asm/xen/page.h
> +++ b/arch/arm/include/asm/xen/page.h
> @@ -36,14 +36,6 @@ extern struct rb_root phys_to_mach;
>  
>  static inline unsigned long pfn_to_mfn(unsigned long pfn)
>  {
> -	unsigned long mfn;
> -
> -	if (phys_to_mach.rb_node != NULL) {
> -		mfn = __pfn_to_mfn(pfn);
> -		if (mfn != INVALID_P2M_ENTRY)
> -			return mfn;
> -	}
> -
>  	return pfn;
>  }
>  
> -- 
> 2.1.4
> 
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