Re: [Xen-devel] [PATCH v3 2/4] xen/arm: implement get/put_page_type

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-07-26 at 19:54 +0100, Stefano Stabellini wrote:
> Add a basic get_page_type and put_page_type implementation: we don't
> care about typecounts so just return success.
> 
> Also remove PGT_shared_page, that is unused.
> 
> 
> Changes in v3:
> 
> - replace get_page_type and put_page_type with an empty implementation.

Tim suggested that we consider adding an assert that the reference count
is non-zero in both of these, since it is incorrect to take a type count
without a reference count (we think).

In the future maybe we should consider refactoring the gnttab code (and
anything else using type counts directly) to use a "pg_make_writable"
arch abstraction so we an hide the type counts inside x86 code where
they properly belong.

> 
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>  xen/arch/arm/dummy.S     |    4 ----
>  xen/arch/arm/mm.c        |   13 +++++++++++++
>  xen/include/asm-arm/mm.h |    1 -
>  3 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/arm/dummy.S b/xen/arch/arm/dummy.S
> index baced25..2b96d22 100644
> --- a/xen/arch/arm/dummy.S
> +++ b/xen/arch/arm/dummy.S
> @@ -22,10 +22,6 @@ DUMMY(arch_get_info_guest);
>  DUMMY(arch_vcpu_reset);
>  NOP(update_vcpu_system_time);
>  
> -/* Page Reference & Type Maintenance */
> -DUMMY(get_page_type);
> -DUMMY(put_page_type);
> -
>  /* Grant Tables */
>  DUMMY(steal_page);
>  
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index e963af9..96a4ca2 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -594,6 +594,19 @@ int get_page(struct page_info *page, struct domain 
> *domain)
>      return 0;
>  }
>  
> +/* Common code requires get_page_type and put_page_type.
> + * We don't care about typecounts so we just do the minimum to make it
> + * happy. */
> +int get_page_type(struct page_info *page, unsigned long type)
> +{
> +    return 1;
> +}
> +
> +void put_page_type(struct page_info *page)
> +{
> +    return;
> +}
> +
>  void gnttab_clear_flag(unsigned long nr, uint16_t *addr)
>  {
>      /*
> diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
> index 53801b0..b37bd35 100644
> --- a/xen/include/asm-arm/mm.h
> +++ b/xen/include/asm-arm/mm.h
> @@ -71,7 +71,6 @@ struct page_info
>  
>  #define PGT_none          PG_mask(0, 4)  /* no special uses of this page   */
>  #define PGT_writable_page PG_mask(7, 4)  /* has writable mappings?         */
> -#define PGT_shared_page   PG_mask(8, 4)  /* CoW sharable page              */
>  #define PGT_type_mask     PG_mask(15, 4) /* Bits 28-31 or 60-63.           */
>  
>   /* Owning guest has pinned this page to its current type? */



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