Re: [Xen-devel] [PATCH] x86/mem_sharing: Rectify test for "empty" physmap entry in sharing_add_to_physmap

[Tim Deegan <tim@xxxxxxx>]

> diff -r f83397dfb6c0 -r 3169fba29613 xen/arch/x86/mm/mem_sharing.c
> --- a/xen/arch/x86/mm/mem_sharing.c
> +++ b/xen/arch/x86/mm/mem_sharing.c
> @@ -1073,9 +1073,10 @@ int mem_sharing_add_to_physmap(struct do
>      if ( spage->sharing->handle != sh )
>          goto err_unlock;
>  
> -    /* Make sure the target page is a hole in the physmap */
> -    if ( mfn_valid(cmfn) ||
> -         (!(p2m_is_ram(cmfn_type))) )
> +    /* Make sure the target page is a hole in the physmap. These are 
> typically
> +     * p2m_mmio_dm, but also accept p2m_invalid and paged out pages. See the
> +     * definition of p2m_is_hole in p2m.h. */
> +    if ( !p2m_is_hole(cmfn_type) || mfn_valid(cmfn) )

As I said last time, the mfn_valid test is wrong for everything except
p2m_paging_in.

I've checked in a reduced version of this that just drops p2m_paging_in
from P2M_HOLE_TYPES (so the pager wins this race instead of the sharer)
which I think will do for 4.2:
http://xenbits.xen.org/hg/staging/xen-unstable.hg/rev/25bdef4493ae
can you check that it makes sense, please?

Cheers,

Tim.

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