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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> ---
>     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@xxxxxxxxxxxxx>

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