Re: [Xen-devel] [PATCH] x86/hvm: don't create a default ioreq server...

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/12/16 17:55, Paul Durrant wrote:
> ...if the domain is not under construction.
>
> If upstream QEMU is in use then it will explicitly create an ioreq server
> rather than implicitly creating the default ioreq server, which is a
> side-effect of reading HVM_PARAM_IOREQ_PFN, HVM_PARAM_BUFIOREQ_PFN,
> or HVM_PARAM_BUFIOREQ_EVTCHN (as is done by legacy QEMUs).
>
> However, if the domain is subsequently saved/migrated then those parameters
> are read and hence the default server will be unnecessarily instantiated.
>
> This patch adds an extra check of the 'creation_finished' flag when those
> HVM params are read and will only instantiate the server if the domain is
> under construction, which will always be the case when QEMU is invoked.
>
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

CC'ing the COLO guys.  Please can you test with this patch?

> ---
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
>  xen/arch/x86/hvm/hvm.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index e0f936b..c531f37 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -5337,7 +5337,16 @@ static int hvmop_get_param(
>      {
>          domid_t domid;
>  
> -        /* May need to create server. */
> +        /*
> +         * It may be necessary to create a default ioreq server here,
> +         * because legacy versions of QEMU are not aware of the new API
> +         * for explicit ioreq server creation. However, if the domain
> +         * is not under construction then it will not be QEMU querying
> +         * the parameters and thus the query should have that side-effect.
> +         */
> +        if ( d->creation_finished )
> +            break;
> +
>          domid = d->arch.hvm_domain.params[HVM_PARAM_DM_DOMAIN];
>          rc = hvm_create_ioreq_server(d, domid, 1,
>                                       HVM_IOREQSRV_BUFIOREQ_LEGACY, NULL);


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