Re: [Xen-devel] [PATCH v7 1/7] x86/p2m: Allow p2m_get_page_from_gfn to return shared entries

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.02.2020 17:12, Tamas K Lengyel wrote:
> The owner domain of shared pages is dom_cow, use that for get_page
> otherwise the function fails to return the correct page under some
> situations. The check if dom_cow should be used was only performed in
> a subset of use-cases. Fixing the error and simplifying the existing check
> since we can't have any shared entries with dom_cow being NULL.

Better, thanks.

> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
> ---
> v7: update commit message
> ---
>  xen/arch/x86/mm/p2m.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> index def13f657b..007fef720d 100644
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -575,11 +575,12 @@ struct page_info *p2m_get_page_from_gfn(
>                  if ( fdom == NULL )
>                      page = NULL;
>              }
> -            else if ( !get_page(page, p2m->domain) &&
> -                      /* Page could be shared */
> -                      (!dom_cow || !p2m_is_shared(*t) ||
> -                       !get_page(page, dom_cow)) )
> -                page = NULL;
> +            else
> +            {
> +                struct domain *d = !p2m_is_shared(*t) ? p2m->domain : 
> dom_cow;
> +                if ( !get_page(page, d) )

There's still a blank line missing between these two lines and ...

> +                    page = NULL;
> +            }
>          }
>          p2m_read_unlock(p2m);
>  
> @@ -595,8 +596,9 @@ struct page_info *p2m_get_page_from_gfn(
>      mfn = get_gfn_type_access(p2m, gfn_x(gfn), t, a, q, NULL);
>      if ( p2m_is_ram(*t) && mfn_valid(mfn) )
>      {
> +        struct domain *d = !p2m_is_shared(*t) ? p2m->domain : dom_cow;
>          page = mfn_to_page(mfn);

... similarly between these two. As indicated before, with them
added
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
despite me still thinking that the title suggests more of a
problem than there really was. (Of course adding the missing
blank lines ought to be easy enough while committing.)

Jan

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