4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Juergen Gross <jgr...@suse.com>

commit 71c208dd54ab971036d83ff6d9837bae4976e623 upstream.

Older Xen versions (4.5 and before) might have problems migrating pv
guests with MSR_IA32_SPEC_CTRL having a non-zero value. So before
suspending zero that MSR and restore it after being resumed.

Signed-off-by: Juergen Gross <jgr...@suse.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Reviewed-by: Jan Beulich <jbeul...@suse.com>
Cc: sta...@vger.kernel.org
Cc: xen-de...@lists.xenproject.org
Cc: boris.ostrov...@oracle.com
Link: https://lkml.kernel.org/r/20180226140818.4849-1-jgr...@suse.com
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 arch/x86/xen/suspend.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c
@@ -1,12 +1,15 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/types.h>
 #include <linux/tick.h>
+#include <linux/percpu-defs.h>
 
 #include <xen/xen.h>
 #include <xen/interface/xen.h>
 #include <xen/grant_table.h>
 #include <xen/events.h>
 
+#include <asm/cpufeatures.h>
+#include <asm/msr-index.h>
 #include <asm/xen/hypercall.h>
 #include <asm/xen/page.h>
 #include <asm/fixmap.h>
@@ -15,6 +18,8 @@
 #include "mmu.h"
 #include "pmu.h"
 
+static DEFINE_PER_CPU(u64, spec_ctrl);
+
 void xen_arch_pre_suspend(void)
 {
        xen_save_time_memory_area();
@@ -35,6 +40,9 @@ void xen_arch_post_suspend(int cancelled
 
 static void xen_vcpu_notify_restore(void *data)
 {
+       if (xen_pv_domain() && boot_cpu_has(X86_FEATURE_SPEC_CTRL))
+               wrmsrl(MSR_IA32_SPEC_CTRL, this_cpu_read(spec_ctrl));
+
        /* Boot processor notified via generic timekeeping_resume() */
        if (smp_processor_id() == 0)
                return;
@@ -44,7 +52,15 @@ static void xen_vcpu_notify_restore(void
 
 static void xen_vcpu_notify_suspend(void *data)
 {
+       u64 tmp;
+
        tick_suspend_local();
+
+       if (xen_pv_domain() && boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
+               rdmsrl(MSR_IA32_SPEC_CTRL, tmp);
+               this_cpu_write(spec_ctrl, tmp);
+               wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+       }
 }
 
 void xen_arch_resume(void)


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