[PATCH 0/2] Remaining prerequisite patches for COLO

[PATCH 0/2] Remaining prerequisite patches for COLO

[Wei Liu]

Konrad Rzeszutek Wilk (1):
  libxc: Document xc_domain_resume

Wen Congyang (1):
  libxc: support to resume uncooperative HVM guests

 tools/libxc/include/xenctrl.h | 50 +++++++++++++++++++++++++++++++++++++++++++
 tools/libxc/xc_resume.c       | 25 ++++++++++++++++++----
 2 files changed, 71 insertions(+), 4 deletions(-)

-- 
2.1.4


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[PATCH 1/2] libxc: support to resume uncooperative HVM guests

[Wei Liu]

From: Wen Congyang <wency@cn.fujitsu.com>

Before this patch:
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 (fast=1)
     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:
               XEN_DOMCTL_resumedomain
     PVHVM:    same with PV
     Pure HVM: Do nothing in modify_returncode, and than call the domctl:
               XEN_DOMCTL_resumedomain
  b. Slow path (fast=0)
     Used when the guest's state have been changed. Will call
     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"
     Pure HVM: Same with PVHVM

After this patch:
1. Suspend
  Unchanged.

2. Resume
  a. Fast path
     Unchanged.
  b. Slow path
     PV:       Unchanged.
     PVHVM:    Call XEN_DOMCTL_resumedomain to resume the guest. Because we
               don't modify the return code, PV drivers will disconnect
               and reconnect.
               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 (except the ones past 32).
               That is the Linux kernel does that - regardless whether the
               SCHEDOP_shutdown:SHUTDOWN_suspend returns 1 or not.
     Pure HVM: Call XEN_DOMCTL_resumedomain to resume the guest.

Under COLO, we will update the guest's state (modify memory, CPU registers,
device state etc). In this case, we cannot use the fast path to resume it.
Keep the return code 0, and use the slow path to resume the guest.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Yang Hongyang <hongyang.yang@easystack.cn>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[ wei: reformat commit message a bit ]
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
 tools/libxc/xc_resume.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/tools/libxc/xc_resume.c b/tools/libxc/xc_resume.c
index 5bf4cf0..6bf7d9c 100644
--- a/tools/libxc/xc_resume.c
+++ b/tools/libxc/xc_resume.c
@@ -109,6 +109,26 @@ 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;
+
+    /*
+     * The domctl XEN_DOMCTL_resumedomain unpause each vcpu. After
+     * the domctl, the guest will run.
+     *
+     * If it is PVHVM, the guest called the hypercall
+     *    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;
@@ -138,10 +158,7 @@ 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 )
     {
-- 
2.1.4


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[PATCH 2/2] libxc: Document xc_domain_resume

[Wei Liu]

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Document the save and suspend mechanism.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
 tools/libxc/include/xenctrl.h | 50 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index a9e4dc1..013a3a3 100644
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -565,6 +565,56 @@ int xc_domain_destroy(xc_interface *xch,
  * This function resumes a suspended domain. The domain should have
  * been previously suspended.
  *
+ * Note that there are 'xc_domain_suspend' as suspending a domain
+ * is quite the endeavour.
+ *
+ * For the purpose of this explanation there are three guests:
+ * PV (using hypercalls for privilgied operations), HVM
+ * (fully hardware virtualized guests using emulated devices for everything),
+ * and PVHVM (PV aware with hardware virtualisation).
+ *
+ * HVM guest are the simplest - they suspend via S3 / S4 and resume from
+ * S3 / S4. Upon resume they have to re-negotiate with the emulated devices.
+ *
+ * PV and PVHVM communicate via hypercalls for suspend (and resume).
+ * For suspend the toolstack initiates the process by writing an value
+ * in XenBus "control/shutdown" with the string "suspend".
+ *
+ * The PV guest stashes anything it deems neccessary in 'struct
+ * start_info' in case of failure (PVHVM may ignore this) and calls
+ * the SCHEDOP_shutdown::SHUTDOWN_suspend hypercall (for PV as
+ * argument it passes the MFN to 'struct start_info').
+ *
+ * And then the guest is suspended.
+ *
+ * The checkpointing or notifying a guest that the suspend failed or
+ * cancelled (in case of checkpoint) is by having the
+ * SCHEDOP_shutdown::SHUTDOWN_suspend hypercall return a non-zero
+ * value.
+ *
+ * The PV and PVHVM resume path are similar. For PV it would be
+ * similar to bootup - figure out where the 'struct start_info' is (or
+ * if the suspend was cancelled aka checkpointed - reuse the saved
+ * values).
+ *
+ * From here on they differ depending whether the guest is PV or PVHVM
+ * in specifics but follow overall the same path:
+ *  - PV: Bringing up the vCPUS,
+ *  - PVHVM: Setup vector callback,
+ *  - Bring up vCPU runstates,
+ *  - Remap the grant tables if checkpointing or setup from scratch,
+ *
+ *
+ * If the resume was not checkpointing (or if suspend was succesful) we would
+ * setup the PV timers and the different PV events. Lastly the PV drivers
+ * re-negotiate with the backend.
+ *
+ * This function would return before the guest started resuming. That is
+ * the guest would be in non-running state and its vCPU context would be
+ * in the the SCHEDOP_shutdown::SHUTDOWN_suspend hypercall return path
+ * (for PV and PVHVM). For HVM it would be in would be in QEMU emulated
+ * BIOS handling S3 suspend.
+ *
  * @parm xch a handle to an open hypervisor interface
  * @parm domid the domain id to resume
  * @parm fast use cooperative resume (guest must support this)
-- 
2.1.4


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Re: [PATCH 0/2] Remaining prerequisite patches for COLO

[Ian Jackson]

Wei Liu writes ("[PATCH 0/2] Remaining prerequisite patches for COLO"):
> Konrad Rzeszutek Wilk (1):
>   libxc: Document xc_domain_resume
> 
> Wen Congyang (1):
>   libxc: support to resume uncooperative HVM guests

Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

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Re: [PATCH 1/2] libxc: support to resume uncooperative HVM guests

[Olaf Hering]

On Thu, Mar 31, Wei Liu wrote:

> +static int xc_domain_resume_hvm(xc_interface *xch, uint32_t domid)
>  #if defined(__i386__) || defined(__x86_64__)
> +        return xc_domain_resume_hvm(xch, domid);

This causes a build error no non-x86.

[  334s] xc_resume.c:112:12: error: 'xc_domain_resume_hvm' defined but not used [-Werror=unused-function]
[  334s]  static int xc_domain_resume_hvm(xc_interface *xch, uint32_t domid)

Olaf

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Re: [PATCH 1/2] libxc: support to resume uncooperative HVM guests

[Wei Liu]

On Fri, Apr 01, 2016 at 05:59:47PM +0200, Olaf Hering wrote:
> On Thu, Mar 31, Wei Liu wrote:
> 
> > +static int xc_domain_resume_hvm(xc_interface *xch, uint32_t domid)
> >  #if defined(__i386__) || defined(__x86_64__)
> > +        return xc_domain_resume_hvm(xch, domid);
> 
> This causes a build error no non-x86.
> 
> [  334s] xc_resume.c:112:12: error: 'xc_domain_resume_hvm' defined but not used [-Werror=unused-function]
> [  334s]  static int xc_domain_resume_hvm(xc_interface *xch, uint32_t domid)
> 

Does this work?


From 6f3252a82168d0025c585dbbaf5817f42f5d1e85 Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2@citrix.com>
Date: Fri, 1 Apr 2016 17:07:52 +0100
Subject: [PATCH] libxc: xc_domain_resume_hvm is used by x86 only

The call site is enclosed by x86 define guards.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
 tools/libxc/xc_resume.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/libxc/xc_resume.c b/tools/libxc/xc_resume.c
index 6bf7d9c..2b6c308 100644
--- a/tools/libxc/xc_resume.c
+++ b/tools/libxc/xc_resume.c
@@ -109,6 +109,7 @@ static int xc_domain_resume_cooperative(xc_interface *xch, uint32_t domid)
     return do_domctl(xch, &domctl);
 }
 
+#if defined(__i386__) || defined(__x86_64__)
 static int xc_domain_resume_hvm(xc_interface *xch, uint32_t domid)
 {
     DECLARE_DOMCTL;
@@ -128,6 +129,7 @@ static int xc_domain_resume_hvm(xc_interface *xch, uint32_t domid)
     domctl.domain = domid;
     return do_domctl(xch, &domctl);
 }
+#endif
 
 static int xc_domain_resume_any(xc_interface *xch, uint32_t domid)
 {
-- 
2.1.4

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Re: [PATCH 1/2] libxc: support to resume uncooperative HVM guests

[Olaf Hering]

On Fri, Apr 01, Wei Liu wrote:

> Does this work?

Most likely yes.

Olaf

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Re: [PATCH 1/2] libxc: support to resume uncooperative HVM guests

[Olaf Hering]

On Fri, Apr 01, Olaf Hering wrote:

> On Fri, Apr 01, Wei Liu wrote:
> 
> > Does this work?
> 
> Most likely yes.

Yes, this change fixes it. Thanks.
There is another failure on arm now, see the other mail "arm: staging
build error in libxl helper_setcallbacks_restore".

Olaf

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