Xen devel - Aug 2013 - [PATCH] xen/balloon: don't set P2M entry for auto translated guest

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@citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 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

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@citrix.com>
> Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

>  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
>