Re: [Xen-devel] [PATCH v3] xen: prevent PVH Dom0 from having pages with more than one ref

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 18/06/14 12:18, Roger Pau Monne wrote:
> On PV guests a reference is taken when a page gets added to the page
> tables, which makes pages added to the page tables have two
> references, but this is not suitable for PVH that doesn't use the
> PVMMU. In the PVH case only one reference has to be taken or else the
> page would not be freed when the memory of the domain is decreased.
>
> Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
> Cc: Keir Fraser <keir@xxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>

Looks much better!

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

> ---
> Changes since v2:
>  - Reword commit message.
>  - Add paging_mode_translate as a condition check to the already
>    exiting gate in the second instance.
>
> Changes since v1:
>  - Fix coding style.
>  - Fix a second occurrence of the same issue.
>  - Use paging_mode_translate instead of is_pvh_domain.
> ---
>  xen/arch/x86/domain_build.c |   13 ++++++++-----
>  1 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/xen/arch/x86/domain_build.c b/xen/arch/x86/domain_build.c
> index ba42fc9..6666093 100644
> --- a/xen/arch/x86/domain_build.c
> +++ b/xen/arch/x86/domain_build.c
> @@ -1137,10 +1137,13 @@ int __init construct_dom0(
>                                      L1_PROT : COMPAT_L1_PROT));
>          l1tab++;
>  
> -        page = mfn_to_page(mfn);
> -        if ( (page->u.inuse.type_info == 0) &&
> -             !get_page_and_type(page, d, PGT_writable_page) )
> -            BUG();
> +        if ( !paging_mode_translate(d) )
> +        {
> +            page = mfn_to_page(mfn);
> +            if ( (page->u.inuse.type_info == 0) &&
> +                 !get_page_and_type(page, d, PGT_writable_page) )
> +                BUG();
> +        }
>      }
>  
>      if ( is_pv_32on64_domain(d) )
> @@ -1300,7 +1303,7 @@ int __init construct_dom0(
>          if ( get_gpfn_from_mfn(mfn) >= count )
>          {
>              BUG_ON(is_pv_32bit_domain(d));
> -            if ( !page->u.inuse.type_info &&
> +            if ( !paging_mode_translate(d) && !page->u.inuse.type_info &&
>                   !get_page_and_type(page, d, PGT_writable_page) )
>                  BUG();
>  


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