Re: [PATCH v6 05/18] tools/libxc: support to resume uncooperative HVM guests

[Wen Congyang <wency@cn.fujitsu.com>]

On 01/26/2016 02:21 AM, Konrad Rzeszutek Wilk wrote:
> On Wed, Dec 30, 2015 at 10:28:55AM +0800, Wen Congyang wrote:
>> Befor this patch:
> 
> s/Befor/Before
>> 1. suspend
>> a. PVHVM and PV: we use the same way to suspend the guest (send the suspend
>>    request to the guest). If the guest doesn't support evtchn, the xenstore
>>    variant will be used, suspending the guest via XenBus control node.
>> b. pure HVM: we call xc_domain_shutdown(..., SHUTDOWN_suspend) to suspend
>>    the guest
>>
>> 2. Resume:
>> a. fast path
> 
> s/fast path/fast path(fast=1)
> 
>>    In this case, we don't change the guest's state. And we will call
>>    libxl__domain_resume(..., 1) to resume the guest.
> 
> Do not change the guest state. We call libxl__domain_resume(.., 1) which
> calls xc_domain_resume(..., 1 /* fast=1*/) to resume the guest.
> 
> 
>>    PV:       modify the return code to 1, and than call the domctl
> 
> s/domctl/domctl:/
>>              XEN_DOMCTL_resumedomain
>>    PVHVM:    same with PV
>>    pure HVM: do nothing in modify_returncode, and than call the domctl:
>>              XEN_DOMCTL_resumedomain
> 
>> b. slow
>>    Used when the guest's state have been changed. And we will call
> 
> s/And we will/Will/
> 
>>    libxl__domain_resume(..., 0) to resume the guest.
>>    PV:       update start info, and reset all secondary CPU states. Than call
>>              the domctl: XEN_DOMCTL_resumedomain
>>    PVHVM:    can not be resumed. You will get the following error message:
>>                  "Cannot resume uncooperative HVM guests"
>>    purt HVM: same with PVHVM
>>
>> After this patch:
>> 1. suspend
>>    unchanged
>>
>> 2. Resume
>> a. fast path:
>>    unchanged
>> b. slow
>>    PV:       unchanged
>>    PVHVM:    call XEN_DOMCTL_resumedomain to resume the guest. Because we
>>              don't modify the return code, the PV driver will disconnect
>>              and reconnect. I am not sure if we should update start info
>>              and reset all secondary CPU states.
> 
> The guest ends up doing the XENMAPSPACE_shared_info XENMEM_add_to_physmap
> hypercall and resetting all of its CPU states to point to the shared_info
> (well except the ones past 32).
> 
> That is the Linux kernel does that - regardless whether the 
> SCHEDOP_shutdown:SHUTDOWN_suspend returns 1 or not.

Yes, I find it in the Linux kernel. Thanks for pointing it out.

> 
>>    Pure HVM: call XEN_DOMCTL_resumedomain to resume the guest.
>>
>> 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. While
>> resuming HVM using slow path is not supported currently, this patch is to
>> make the resume call do not fail.
> 
> s/do/to/
>>
>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
>> Signed-off-by: Yang Hongyang <hongyang.yang@easystack.cn>
>> ---
>>  tools/libxc/xc_resume.c | 24 ++++++++++++++++++++----
>>  1 file changed, 20 insertions(+), 4 deletions(-)
>>
>> diff --git a/tools/libxc/xc_resume.c b/tools/libxc/xc_resume.c
>> index 87d4324..503e4f8 100644
>> --- a/tools/libxc/xc_resume.c
>> +++ b/tools/libxc/xc_resume.c
>> @@ -108,6 +108,25 @@ 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;
>> +
>> +    /*
>> +     * This domctl XEN_DOMCTL_resumedomain just unpause each vcpu. After
> 
> s/This/The/
> s/just//
>> +     * this domctl, the guest will run.
> s/this/the/
> 
>> +     *
>> +     * If it is PVHVM, the guest called the hypercall HYPERVISOR_sched_op
> 
> s/HYPERVISOR_sched_op/SCHEDOP_shutdown:SHUTDOWN_suspend/
>> +     * to suspend itself. We don't modify the return code, so the PV driver
>> +     * will disconnect and reconnect.
>> +     *
>> +     * If it is a HVM, the guest will continue running.
>> +     */
>> +    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;
>> @@ -137,10 +156,7 @@ 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 )
>>      {
>> -- 
>> 2.5.0
>>
>>
>>
>>
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>> Xen-devel@lists.xen.org
>> http://lists.xen.org/xen-devel
> 
> 
> .
>