Re: [Xen-devel] [PATCH v2 21/24] xen/arm: page: Describe the layout of flags used to update page tables

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 12 Sep 2017, Julien Grall wrote:
> Currently, the flags used to update page tables (i.e PAGE_HYPERVISOR_*)
> only contains the memory attribute index. Follow-up patches will add
> more information in it. So document the current layout.
> 
> At the same time introduce PAGE_AI_MASK to get the memory attribute
> index easily.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>     Andre, I have slightly update the commit message to show that we
>     just describe the current layout. Hope you are fine with keeping
>     your reviewed-by.
> 
>     Changes in v2:
>         - Slightly update the commit message to specify we describe the
>         current layout.
>         - Add Andre's reviewed-by
> ---
>  xen/arch/arm/mm.c          | 2 +-
>  xen/include/asm-arm/page.h | 7 +++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 3379d29f8a..8a56f37821 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -1021,7 +1021,7 @@ static int create_xen_entries(enum xenmap_operation op,
>                  }
>                  if ( op == RESERVE )
>                      break;
> -                pte = mfn_to_xen_entry(mfn, flags);
> +                pte = mfn_to_xen_entry(mfn, PAGE_AI_MASK(flags));
>                  pte.pt.table = 1;
>                  write_pte(entry, pte);
>                  break;
> diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
> index 088746828d..4022b7dc33 100644
> --- a/xen/include/asm-arm/page.h
> +++ b/xen/include/asm-arm/page.h
> @@ -62,6 +62,13 @@
>  #define MAIR0VAL (MAIRVAL & 0xffffffff)
>  #define MAIR1VAL (MAIRVAL >> 32)
>  
> +/*
> + * Layout of the flags used for updating the hypervisor page tables
> + *
> + * [0:2] Memory Attribute Index
> + */
> +#define PAGE_AI_MASK(x) ((x) & 0x7U)
> +
>  #define PAGE_HYPERVISOR         (MT_NORMAL)
>  #define PAGE_HYPERVISOR_NOCACHE (MT_DEVICE_nGnRE)
>  #define PAGE_HYPERVISOR_WC      (MT_NORMAL_NC)
> -- 
> 2.11.0
> 

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