Re: [Xen-devel] [PATCH 24/27] xen/arm: page: Describe the layout of flags used to update page tables

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 14/08/17 15:24, 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.
> 
> At the same time introduce PAGE_AI_MASK to get the memory attribute
> index easily.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

I wonder if that should be merged with the next patch, to explain the
reason for it. As it stands now it just applies a mask to some existing
call, which looks a bit suspicious.
But that's just a nit and the patch itself is fine, so:

Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>

Cheers,
Andre.

> ---
>  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 411fe02842..cd7bcf7aca 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 d9dac92e73..1bf8e9d012 100644
> --- a/xen/include/asm-arm/page.h
> +++ b/xen/include/asm-arm/page.h
> @@ -63,6 +63,13 @@
>  #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)
> 

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