x86/xen: Zero MSR_IA32_SPEC_CTRL before suspend

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 <jgross@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Cc: stable@vger.kernel.org
Cc: xen-devel@lists.xenproject.org
Cc: boris.ostrovsky@oracle.com
Link: https://lkml.kernel.org/r/20180226140818.4849-1-jgross@suse.com

1 files changed, 16 insertions, 0 deletions

diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
index d9f96cc5d743..1d83152c761b 100644
--- 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 *data)
 
 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)