RE: [Xen-API] [PATCH] Prevent the ballooning daemon from setting a bad initial balloon target

[Dave Scott <Dave.Scott@xxxxxxxxxxxxx>]

Oops I forgot the signed-off-by line. Will fix and resubmit :)

> -----Original Message-----
> From: xen-api-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-api-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of David Scott
> Sent: 30 November 2009 13:55
> To: xen-api@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-API] [PATCH] Prevent the ballooning daemon from setting a
> bad initial balloon target
> 
> # HG changeset patch
> # User David Scott <dave.scott@xxxxxxxxxxxxx> # Date 1259589197 0 #
> Node ID 9e26e414cead7308a9d746f3028a69ae8cf5dc94
> # Parent  87733f43712b5e3653d0651f10e34b9634f79c27
> CA-35406: refrain from setting a domain's target unless we think it
> 'can_balloon' ie it has exposed feature-balloon.
> 
> This fixes the problem generated by the following interleaving:
> 
> xapi                                squeezed
> -----------------------------------------------------------------------
> ---
> reserve required memory + overhead
> create domain
> invoke domain builder
>                                     observes domain with no feature-
> balloon
>                                     sets maxmem = requred memory +
> overhead
>                                     sets target = maxmem [1]
> 
> unpauses domain
> 
>                                   observes feature-balloon
>                                   sets memory-offset = -overhead (!)
>                                   declares domain uncooperative
> 
> 
> [1] 519:f509339c8f74 avoid setting target > maxmem
> 
> diff -r 87733f43712b -r 9e26e414cead ocaml/xenops/squeeze_xen.ml
> --- a/ocaml/xenops/squeeze_xen.ml     Mon Nov 30 13:53:14 2009 +0000
> +++ b/ocaml/xenops/squeeze_xen.ml     Mon Nov 30 13:53:17 2009 +0000
> @@ -371,11 +371,18 @@
>               then failwith "Proposed target is negative (domid %d): %Ld"
> domid target_kib;
>               let cnx = (xc, xs) in
>               let memory_max_kib = Domain.get_maxmem cnx domid in
> +             (* We only set the target of a domain if it has exposed
> feature-balloon: otherwise
> +                we can screw up the memory-offset calculations for
> partially-built domains. *)
> +             let can_balloon = Domain.get_feature_balloon cnx domid in
>               if target_kib > memory_max_kib then begin
>                 Domain.set_maxmem_noexn cnx domid target_kib;
> -               Domain.set_target_noexn cnx domid target_kib;
> +               if can_balloon
> +               then Domain.set_target_noexn cnx domid target_kib
> +               else debug "Not setting target for domid: %d since no
> +feature-balloon. Setting maxmem to %Ld" domid target_kib;
>               end else begin
> -               Domain.set_target_noexn cnx domid target_kib;
> +               if can_balloon
> +               then Domain.set_target_noexn cnx domid target_kib
> +               else debug "Not setting target for domid: %d since no
> +feature-balloon. Setting maxmem to %Ld" domid target_kib;
>                 Domain.set_maxmem_noexn cnx domid target_kib;
>               end
>       with e ->
> 1 file changed, 9 insertions(+), 2 deletions(-)
> ocaml/xenops/squeeze_xen.ml |   11 +++++++++--
> 


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