Re: [Xen-devel] [PATCH 08/22] xen/arm: p2m: Simplify p2m type check by using bitmask

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 20 Jul 2016, Julien Grall wrote:
> The resulting assembly code for the macros is much simpler and will
> never contain more than one instruction branch.
> 
> The idea is taken from x86 (see include/asm-x86/p2m.h). Also move the
> two helpers earlier to keep all the p2m type definitions together.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


>  xen/include/asm-arm/p2m.h | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
> index dbbcefe..3091c04 100644
> --- a/xen/include/asm-arm/p2m.h
> +++ b/xen/include/asm-arm/p2m.h
> @@ -97,6 +97,17 @@ typedef enum {
>      p2m_max_real_type,  /* Types after this won't be store in the p2m */
>  } p2m_type_t;
>  
> +/* We use bitmaps and mask to handle groups of types */
> +#define p2m_to_mask(_t) (1UL << (_t))
> +
> +/* RAM types, which map to real machine frames */
> +#define P2M_RAM_TYPES (p2m_to_mask(p2m_ram_rw) |        \
> +                       p2m_to_mask(p2m_ram_ro))
> +
> +/* Useful predicates */
> +#define p2m_is_ram(_t) (p2m_to_mask(_t) & P2M_RAM_TYPES)
> +#define p2m_is_foreign(_t) (p2m_to_mask(_t) & p2m_to_mask(p2m_map_foreign))
> +
>  static inline
>  void p2m_mem_access_emulate_check(struct vcpu *v,
>                                    const vm_event_response_t *rsp)
> @@ -110,9 +121,6 @@ void p2m_altp2m_check(struct vcpu *v, uint16_t idx)
>      /* Not supported on ARM. */
>  }
>  
> -#define p2m_is_foreign(_t)  ((_t) == p2m_map_foreign)
> -#define p2m_is_ram(_t)      ((_t) == p2m_ram_rw || (_t) == p2m_ram_ro)
> -
>  /* Initialise vmid allocator */
>  void p2m_vmid_allocator_init(void);
>  
> -- 
> 1.9.1
> 

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