linux-kernel - Re: [PATCH v2 01/20] xen: Add Xen specific page definition

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Date:	Thu, 16 Jul 2015 15:19:31 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Julien Grall <julien.grall@...rix.com>
CC:	<xen-devel@...ts.xenproject.org>,
	<linux-arm-kernel@...ts.infradead.org>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"David Vrabel" <david.vrabel@...rix.com>
Subject: Re: [PATCH v2 01/20] xen: Add Xen specific page definition

On Thu, 9 Jul 2015, Julien Grall wrote:
> The Xen hypercall interface is always using 4K page granularity on ARM
> and x86 architecture.
> 
> With the incoming support of 64K page granularity for ARM64 guest, it
> won't be possible to re-use the Linux page definition in Xen drivers.
> 
> Introduce Xen page definition helpers based on the Linux page
> definition. They have exactly the same name but prefixed with
> XEN_/xen_ prefix.
> 
> Also modify page_to_pfn to use new Xen page definition.
> 
> Signed-off-by: Julien Grall <julien.grall@...rix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> ---
>     I'm wondering if we should drop page_to_pfn has the macro will likely
>     misuse when Linux is using 64KB page granularity.
> 
>     Changes in v2:
>         - Add XEN_PFN_UP
>         - Add a comment describing the behavior of page_to_pfn
> ---
>  include/xen/page.h | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/include/xen/page.h b/include/xen/page.h
> index c5ed20b..8ebd37b 100644
> --- a/include/xen/page.h
> +++ b/include/xen/page.h
> @@ -1,11 +1,30 @@
>  #ifndef _XEN_PAGE_H
>  #define _XEN_PAGE_H
>  
> +#include <asm/page.h>
> +
> +/* The hypercall interface supports only 4KB page */
> +#define XEN_PAGE_SHIFT	12
> +#define XEN_PAGE_SIZE	(_AC(1,UL) << XEN_PAGE_SHIFT)
> +#define XEN_PAGE_MASK	(~(XEN_PAGE_SIZE-1))
> +#define xen_offset_in_page(p)	((unsigned long)(p) & ~XEN_PAGE_MASK)
> +#define xen_pfn_to_page(pfn)	\

I think it would be clearer if you called the parameter "xen_pfn"
instead of "pfn".


> +	((pfn_to_page(((unsigned long)(pfn) << XEN_PAGE_SHIFT) >> PAGE_SHIFT)))
> +#define xen_page_to_pfn(page)	\
> +	(((page_to_pfn(page)) << PAGE_SHIFT) >> XEN_PAGE_SHIFT)


It would be nice to have a comment:

/* assume PAGE_SIZE is a multiple of XEN_PAGE_SIZE */


> +#define XEN_PFN_PER_PAGE	(PAGE_SIZE / XEN_PAGE_SIZE)
> +
> +#define XEN_PFN_DOWN(x)	((x) >> XEN_PAGE_SHIFT)
> +#define XEN_PFN_UP(x)	(((x) + XEN_PAGE_SIZE-1) >> XEN_PAGE_SHIFT)
> +#define XEN_PFN_PHYS(x)	((phys_addr_t)(x) << XEN_PAGE_SHIFT)
> +
>  #include <asm/xen/page.h>
>  
> +/* Return the MFN associated to the first 4KB of the page */
>  static inline unsigned long page_to_mfn(struct page *page)
>  {
> -	return pfn_to_mfn(page_to_pfn(page));
> +	return pfn_to_mfn(xen_page_to_pfn(page));
>  }
>  
>  struct xen_memory_region {


Aside from the two minor suggestions:

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