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[Xen-devel] [PATCH v4 --for 4.6 COLOPre 11/25] tools/libxc: support to resume uncooperative HVM guests

From: Wen Congyang <wency@xxxxxxxxxxxxxx>

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
   In this case, we don't change the guest's state.
   PV: modify the return code to 1, and than call the domctl:
   PVHVM: same with PV
   HVM: do nothing in modify_returncode, and than call the domctl:
b. slow
   Used when the guest's state have been changed.
   PV: update start info, and reset all secondary CPU states. Than call the
   domctl: XEN_DOMCTL_resumedomain
   PVHVM and HVM can not be resumed.

For PVHVM, in my test, only call the domctl: XEN_DOMCTL_resumedomain
can work. I am not sure if we should update start info and reset all
secondary CPU states.

For pure HVM guest, in my test, only call the domctl:
XEN_DOMCTL_resumedomain can work.

So we can call libxl__domain_resume(..., 1) if we don't change the guest
state, otherwise call libxl__domain_resume(..., 0).

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.

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)
+    /*
+     * 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)
@@ -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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