Re: [Xen-devel] [PATCH v2 COLOPre 02/13] tools/libxc: support to resume uncooperative HVM guests

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-06-08 at 11:43 +0800, Yang Hongyang wrote:
> From: Wen Congyang <wency@xxxxxxxxxxxxxx>
> 
> For PVHVM, the hypercall return code is 0, and it can be resumed
> in a new domain context.
> we suspend PVHVM and resume it is like this:
> 1. suspend it via evtchn
> 2. modifty the return code to 1
> 3. the guest know that the suspend is cancelled, we will use fast path
>    to resume it.
> 
> Under COLO, we will update the guest's state(modify memory, cpu's registers,
> device status...). In this case, we cannot use the fast path to resume it.
> Keep the return code 0, and use a slow path to resume the guest. We have
> updated the guest state, so we call it a new domain context.
> 
> For HVM, the hypercall is a NOP.

This doesn't match my reading of domain_resume on the Xen side, which is
the ultimate effect of this hypercall. It seems to unpause the domain
(and all vcpus) regardless of the domain type, including PVHVM vs HVM
(which isn't something Xen is generally aware of anyway).

I also can't really follow the stuff about PVHVM vs HVM vs uncooperative
guests, and I certainly can't see where the PVHVM vs HVM distinction is
made in this patch.

Ian.


> 
> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
> Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>
> ---
>  tools/libxc/xc_resume.c | 22 ++++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/libxc/xc_resume.c b/tools/libxc/xc_resume.c
> index e67bebd..bd82334 100644
> --- a/tools/libxc/xc_resume.c
> +++ b/tools/libxc/xc_resume.c
> @@ -109,6 +109,23 @@ static int xc_domain_resume_cooperative(xc_interface 
> *xch, uint32_t domid)
>      return do_domctl(xch, &domctl);
>  }
>  
> +static int xc_domain_resume_hvm(xc_interface *xch, uint32_t domid)
> +{
> +    DECLARE_DOMCTL;
> +
> +    /*
> +     * If it is PVHVM, the hypercall return code is 0, because this
> +     * is not a fast path resume, we do not modify_returncode as in
> +     * xc_domain_resume_cooperative.
> +     * (resuming it in a new domain context)
> +     *
> +     * If it is a HVM, the hypercall is a NOP.
> +     */
> +    domctl.cmd = XEN_DOMCTL_resumedomain;
> +    domctl.domain = domid;
> +    return do_domctl(xch, &domctl);
> +}
> +
>  static int xc_domain_resume_any(xc_interface *xch, uint32_t domid)
>  {
>      DECLARE_DOMCTL;
> @@ -138,10 +155,7 @@ static int xc_domain_resume_any(xc_interface *xch, 
> uint32_t domid)
>       */
>  #if defined(__i386__) || defined(__x86_64__)
>      if ( info.hvm )
> -    {
> -        ERROR("Cannot resume uncooperative HVM guests");
> -        return rc;
> -    }
> +        return xc_domain_resume_hvm(xch, domid);
>  
>      if ( xc_domain_get_guest_width(xch, domid, &dinfo->guest_width) != 0 )
>      {



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