Re: [Xen-devel] [PATCH] xen/balloon: don't set P2M entry for auto translated guest

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 27 Aug 2013, Wei Liu wrote:
> In commit cd9151e2: xen/balloon: set a mapping for ballooned out pages
> we have the ballooned out page's mapping set to a scratch page.
> 
> That commit also sets the P2M entry of ballooned out page to the scratch
> page's MFN. This is necessary for PV guest but not for HVM guest. On the
> other hand, setting the P2M entry would trigger BUG_ON in
> __set_phys_to_machine.
> 
> The correct thing to do here is to avoid calling __set_phys_to_machine
> for auto translated guest.
> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


>  drivers/xen/balloon.c |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index a3dc75d..3101cf6 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -430,8 +430,13 @@ static enum bp_state decrease_reservation(unsigned long 
> nr_pages, gfp_t gfp)
>       /* No more mappings: invalidate P2M and add to balloon. */
>       for (i = 0; i < nr_pages; i++) {
>               pfn = mfn_to_pfn(frame_list[i]);
> -             __set_phys_to_machine(pfn,
> -                             
> pfn_to_mfn(page_to_pfn(__get_cpu_var(balloon_scratch_page))));
> +             if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> +                     unsigned long p;
> +                     struct page *pg;
> +                     pg = __get_cpu_var(balloon_scratch_page);
> +                     p = page_to_pfn(pg);
> +                     __set_phys_to_machine(pfn, pfn_to_mfn(p));
> +             }
>               balloon_append(pfn_to_page(pfn));
>       }
>  
> -- 
> 1.7.10.4
> 

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