Re: [PATCH v3 04/20] xen/grant: Introduce helpers to split a page into grant

[Stefano Stabellini]

On Fri, 7 Aug 2015, Julien Grall wrote:
> Currently, a grant is always based on the Xen page granularity (i.e
> 4KB). When Linux is using a different page granularity, a single page
> will be split between multiple grants.
> 
> The new helpers will be in charge to split the Linux page into grants and
                                    ^ of splitting

> call a function given by the caller on each grant.
> 
> Also provide an helper to count the number of grants within a given
> contiguous region.
> 
> Note that the x86/include/asm/xen/page.h is now including
> xen/interface/grant_table.h rather than xen/grant_table.h. It's
> necessary because xen/grant_table.h depends on asm/xen/page.h and will
> break the compilation. Furthermore, only definition in
> interface/grant_table.h was required.
                           ^ is

> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>

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


> ---
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> 
>     Changes in v3:
>         - Fix error reported by checkpatch.pl
>         - Typoes
>         - s/pfn/xen_pfn/ in gnttab_foreach_grant
>         - Drop the possibility to use less data. The complexity is moved
>         in netback which is the only user
>         - Rename gnttab_foreach_grant into gnttab_foreach_grant_in_range
>         - s/offset/start/ in gnttab_count_grant and update the
>         description of the parameter
>         - s/mfn/gfn base on the new terminologies
>         - Add EXPORT_SYMBOL_GPL for gnttab_foreach_grant_in_range
>         - Use xen_offset_in_page and XEN_PFN_DOWN whenever it's possible
>         - Fix compilation on x86.
> 
>     Changes in v2:
>         - Patch added
> ---
>  arch/x86/include/asm/xen/page.h |  2 +-
>  drivers/xen/grant-table.c       | 26 +++++++++++++++++++++++++
>  include/xen/grant_table.h       | 42 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 69 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index 0b762f6..501479e 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -12,7 +12,7 @@
>  #include <asm/pgtable.h>
>  
>  #include <xen/interface/xen.h>
> -#include <xen/grant_table.h>
> +#include <xen/interface/grant_table.h>
>  #include <xen/features.h>
>  
>  /* Xen machine address */
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 62f591f..94ae0fd 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -776,6 +776,32 @@ void gnttab_batch_copy(struct gnttab_copy *batch, unsigned count)
>  }
>  EXPORT_SYMBOL_GPL(gnttab_batch_copy);
>  
> +void gnttab_foreach_grant_in_range(struct page *page,
> +				   unsigned int offset,
> +				   unsigned int len,
> +				   xen_grant_fn_t fn,
> +				   void *data)
> +{
> +	unsigned int goffset;
> +	unsigned int glen;
> +	unsigned long xen_pfn;
> +
> +	len = min_t(unsigned int, PAGE_SIZE - offset, len);
> +	goffset = xen_offset_in_page(offset);
> +
> +	xen_pfn = xen_page_to_pfn(page) + XEN_PFN_DOWN(offset);
> +
> +	while (len) {
> +		glen = min_t(unsigned int, XEN_PAGE_SIZE - goffset, len);
> +		fn(pfn_to_gfn(xen_pfn), goffset, glen, data);
> +
> +		goffset = 0;
> +		xen_pfn++;
> +		len -= glen;
> +	}
> +}
> +EXPORT_SYMBOL_GPL(gnttab_foreach_grant_in_range);
> +
>  int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
>  		    struct gnttab_map_grant_ref *kmap_ops,
>  		    struct page **pages, unsigned int count)
> diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
> index 4478f4b..2a8ebe8 100644
> --- a/include/xen/grant_table.h
> +++ b/include/xen/grant_table.h
> @@ -45,8 +45,10 @@
>  #include <asm/xen/hypervisor.h>
>  
>  #include <xen/features.h>
> +#include <xen/page.h>
>  #include <linux/mm_types.h>
>  #include <linux/page-flags.h>
> +#include <linux/kernel.h>
>  
>  #define GNTTAB_RESERVED_XENSTORE 1
>  
> @@ -224,4 +226,44 @@ static inline struct xen_page_foreign *xen_page_foreign(struct page *page)
>  #endif
>  }
>  
> +/* Split Linux page in chunk of the size of the grant and call fn
> + *
> + * Parameters of fn:
> + *	gfn: guest frame number
> + *	offset: offset in the grant
> + *	len: length of the data in the grant.
> + *	data: internal information
> + */
> +typedef void (*xen_grant_fn_t)(unsigned long gfn, unsigned int offset,
> +			       unsigned int len, void *data);
> +
> +void gnttab_foreach_grant_in_range(struct page *page,
> +				   unsigned int offset,
> +				   unsigned int len,
> +				   xen_grant_fn_t fn,
> +				   void *data);
> +
> +/* Helper to get to call fn only on the first "grant chunk" */
> +static inline void gnttab_one_grant(struct page *page, unsigned int offset,
> +				    unsigned len, xen_grant_fn_t fn,
> +				    void *data)
> +{
> +	/* The first request is limited to the size of one grant */
> +	len = min_t(unsigned int, XEN_PAGE_SIZE - (offset & ~XEN_PAGE_MASK),
> +		    len);
> +
> +	gnttab_foreach_grant_in_range(page, offset, len, fn, data);
> +}
> +
> +/* Get the number of grant in a specified region
> + *
> + * start: Offset from the beginning of the first page
> + * len: total length of data (can cross multiple page)
> + */
> +static inline unsigned int gnttab_count_grant(unsigned int start,
> +					      unsigned int len)
> +{
> +	return XEN_PFN_UP(xen_offset_in_page(start) + len);
> +}
> +
>  #endif /* __ASM_GNTTAB_H__ */
> -- 
> 2.1.4
> 
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