From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH Remus v1 5/8] tools/libxc: defer the setting
 of HVM_PARAM_IDENT_PT
Date: Thu, 7 May 2015 11:35:17 +0100
Message-ID: <554B3FE5.2060300@citrix.com>
References: <1430980646-316-1-git-send-email-yanghy@cn.fujitsu.com>
	<1430980646-316-6-git-send-email-yanghy@cn.fujitsu.com>
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To: Yang Hongyang <yanghy@cn.fujitsu.com>, xen-devel@lists.xen.org
Cc: wei.liu2@citrix.com, ian.campbell@citrix.com, wency@cn.fujitsu.com, eddie.dong@intel.com, yunhong.jiang@intel.com, ian.jackson@eu.citrix.com, rshriram@cs.ubc.ca
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On 07/05/15 07:37, Yang Hongyang wrote:
> Set the hvm param HVM_PARAM_IDENT_PT second time will fail.
> So defer the setting of HVM_PARAM_IDENT_PT.
>
> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>

I would argue that this is a Xen bug, not a migration bug.  There is
nothing conceptually wrong with setting this param multiple times.

Please try the following hypervisor patch instead:

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 3a09439..9ee56b3 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -5748,12 +5748,13 @@ long do_hvm_op(unsigned long op,
XEN_GUEST_HANDLE_PARAM(void) arg)
                 if ( curr_d == d )
                     break;
 
-                rc = -EINVAL;
-                if ( d->arch.hvm_domain.params[a.index] != 0 )
-                    break;
-
                 rc = 0;
-                if ( !paging_mode_hap(d) )
+                d->arch.hvm_domain.params[a.index] = a.value;
+                /*
+                 * Only actually required for VT-x lacking
unrestricted_guest
+                 * capabilities.  Short circuit the pause if possible.
+                 */
+                if ( !paging_mode_hap(d) || !cpu_has_vmx )
                     break;
 
                 /*
@@ -5767,7 +5768,6 @@ long do_hvm_op(unsigned long op,
XEN_GUEST_HANDLE_PARAM(void) arg)
 
                 rc = 0;
                 domain_pause(d);
-                d->arch.hvm_domain.params[a.index] = a.value;
                 for_each_vcpu ( d, v )
                     paging_update_cr3(v);
                 domain_unpause(d);