Re: [PATCH v4 11/12] x86/hvm/ioreq: defer mapping gfns until they are actually requsted

[Wei Liu <wei.liu2@citrix.com>]

On Tue, Sep 05, 2017 at 12:37:15PM +0100, Paul Durrant wrote:
> A subsequent patch will introduce a new scheme to allow an emulator to
> map ioreq server pages directly from Xen rather than the guest P2M.
> 
> This patch lays the groundwork for that change by deferring mapping of
> gfns until their values are requested by an emulator. To that end, the
> pad field of the xen_dm_op_get_ioreq_server_info structure is re-purposed
> to a flags field and new flag, XEN_DMOP_no_gfns, defined which modifies the
> behaviour of XEN_DMOP_get_ioreq_server_info to allow the caller to avoid
> requesting the gfn values.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> Cc: Wei Liu <wei.liu2@citrix.com>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> Cc: George Dunlap <George.Dunlap@eu.citrix.com>
> Cc: Jan Beulich <jbeulich@suse.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Tim Deegan <tim@xen.org>
> 
> v3:
>  - Updated in response to review comments from Wei and Roger.
>  - Added a HANDLE_BUFIOREQ macro to make the code neater.
>  - This patch no longer introduces a security vulnerability since there
>    is now an explicit limit on the number of ioreq servers that may be
>    created for any one domain.
> ---
>  tools/libs/devicemodel/core.c                   |  8 +++++
>  tools/libs/devicemodel/include/xendevicemodel.h |  6 ++--
>  xen/arch/x86/hvm/dm.c                           |  9 ++++--
>  xen/arch/x86/hvm/ioreq.c                        | 41 +++++++++++++------------
>  xen/include/asm-x86/hvm/domain.h                |  2 +-
>  xen/include/public/hvm/dm_op.h                  | 32 +++++++++++--------
>  6 files changed, 59 insertions(+), 39 deletions(-)
> 
> diff --git a/tools/libs/devicemodel/core.c b/tools/libs/devicemodel/core.c
> index fcb260d29b..28958934bf 100644
> --- a/tools/libs/devicemodel/core.c
> +++ b/tools/libs/devicemodel/core.c
> @@ -188,6 +188,14 @@ int xendevicemodel_get_ioreq_server_info(
>  
>      data->id = id;
>  
> +    /*
> +     * If the caller is not requesting gfn values then instruct the
> +     * hypercall not to retrieve them as this may cause them to be
> +     * mapped.
> +     */
> +    if (!ioreq_gfn && !bufioreq_gfn)
> +        data->flags |= XEN_DMOP_no_gfns;
> +

Sorry for not having noticed this earlier.

This is a slight change to a stable API. The new functionality is an
extension of the old. I would suggest you bump the minor number of this
library as well.

The rest looks good to me.

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