Re: [Xen-devel] [RFC 06/16] xen/arm: p2m: Introduce a helper to generate P2M table entry from a page

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 8 Oct 2018, Julien Grall wrote:
> Generate P2M table entry requires to set some default values which are
> worth to explain in a comment. At the moment, there are 2 places where
> such entry are created but only one as proper comment.
> 
> Some move the code to generate P2M table entry in a separate helper.
> This will be helpful in a follow-up patch to make modification on the
> defaults.
> 
> At the same time, switch the default access from p2m->default_access to
> p2m_access_rwx. This should not matter as permission are ignored for
> table by the hardware.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

> ---
>  xen/arch/arm/p2m.c | 25 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 8fffb42889..6c76298ebc 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -538,6 +538,16 @@ static lpae_t mfn_to_p2m_entry(mfn_t mfn, p2m_type_t t, 
> p2m_access_t a)
>      return e;
>  }
>  
> +/* Generate table entry with correct attributes. */
> +static lpae_t page_to_p2m_table(struct page_info *page)
> +{
> +    /*
> +     * The access value does not matter because the hardware will ignore
> +     * the permission fields for table entry.
> +     */
> +    return mfn_to_p2m_entry(page_to_mfn(page), p2m_invalid, p2m_access_rwx);
> +}
> +
>  static inline void p2m_write_pte(lpae_t *p, lpae_t pte, bool clean_pte)
>  {
>      write_pte(p, pte);
> @@ -558,7 +568,6 @@ static int p2m_create_table(struct p2m_domain *p2m, 
> lpae_t *entry)
>  {
>      struct page_info *page;
>      lpae_t *p;
> -    lpae_t pte;
>  
>      ASSERT(!lpae_is_valid(*entry));
>  
> @@ -576,14 +585,7 @@ static int p2m_create_table(struct p2m_domain *p2m, 
> lpae_t *entry)
>  
>      unmap_domain_page(p);
>  
> -    /*
> -     * The access value does not matter because the hardware will ignore
> -     * the permission fields for table entry.
> -     */
> -    pte = mfn_to_p2m_entry(page_to_mfn(page), p2m_invalid,
> -                           p2m->default_access);
> -
> -    p2m_write_pte(entry, pte, p2m->clean_pte);
> +    p2m_write_pte(entry, page_to_p2m_table(page), p2m->clean_pte);
>  
>      return 0;
>  }
> @@ -764,14 +766,11 @@ static bool p2m_split_superpage(struct p2m_domain *p2m, 
> lpae_t *entry,
>  
>      unmap_domain_page(table);
>  
> -    pte = mfn_to_p2m_entry(page_to_mfn(page), p2m_invalid,
> -                           p2m->default_access);
> -
>      /*
>       * Even if we failed, we should install the newly allocated LPAE
>       * entry. The caller will be in charge to free the sub-tree.
>       */
> -    p2m_write_pte(entry, pte, p2m->clean_pte);
> +    p2m_write_pte(entry, page_to_p2m_table(page), p2m->clean_pte);
>  
>      return rv;
>  }
> -- 
> 2.11.0
> 

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