Re: [Xen-devel] [PATCH v2 04/10] xen/arm: Store p2m type in each page of the guest

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-12-09 at 03:34 +0000, Julien Grall wrote:
> Use the field 'avail' to store the type of the page. Rename it to 'p2mt' for
> convenience.

The p2m is redundant in most uses, and the t isn't very descriptive. I
think "type" would be fine.

> The information stored in this field will be retrieved in a future patch to
> hange the behaviour when the page is removed.

"change"

> Also introduce guest_physmap_add_entry to map and set a specific p2m type for
> a page.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> 
> ---
>     Changes in v2:
>         - Rename 'avail' field to 'p2mt' in the p2m structure
>         - Add BUILD_BUG_ON to check if the enum value will fit in the field
>         - Implement grant mapping type
> ---
>  xen/arch/arm/p2m.c         |   58 
> ++++++++++++++++++++++++++++++++------------
>  xen/include/asm-arm/p2m.h  |   18 +++++++++++---
>  xen/include/asm-arm/page.h |    2 +-
>  3 files changed, 58 insertions(+), 20 deletions(-)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 8f8b47e..e43804c 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -124,7 +124,8 @@ int p2m_pod_decrease_reservation(struct domain *d,
>      return -ENOSYS;
>  }
>  
> -static lpae_t mfn_to_p2m_entry(unsigned long mfn, unsigned int mattr)
> +static lpae_t mfn_to_p2m_entry(unsigned long mfn, unsigned int mattr,
> +                               p2m_type_t t)
>  {
>      paddr_t pa = ((paddr_t) mfn) << PAGE_SHIFT;
>      lpae_t e = (lpae_t) {
> @@ -132,12 +133,34 @@ static lpae_t mfn_to_p2m_entry(unsigned long mfn, 
> unsigned int mattr)
>          .p2m.af = 1,
>          .p2m.sh = LPAE_SH_OUTER,
>          .p2m.read = 1,
> -        .p2m.write = 1,
>          .p2m.mattr = mattr,
>          .p2m.table = 1,
>          .p2m.valid = 1,
> +        .p2m.p2mt = t,
>      };
>  
> +    BUILD_BUG_ON(p2m_max_real_type > (2 << 4));
> +
> +    switch (t)
> +    {
> +    case p2m_grant_map_rw:
> +        e.p2m.xn = 1;
> +        /* Fallthrough */
> +    case p2m_ram_rw:
> +    case p2m_mmio_direct:
> +    case p2m_map_foreign:
> +        e.p2m.write = 1;
> +        break;
> +
> +    case p2m_grant_map_ro:
> +        e.p2m.xn = 1;
> +        /* Fallthrough */
> +    case p2m_invalid:
> +    case p2m_ram_ro:
> +    default:

I think you've enumerated all the options, so it is better to leave out
the default -- then at least some compilers will complain if we add a
new type and forget to add it here.

The bulk of the patch looks good though, thanks.

Ian.



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