[PATCH 3.16 311/410] x86/xen: Zero MSR_IA32_SPEC_CTRL before suspend

[Ben Hutchings]

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Juergen Gross <jgross@xxxxxxxx>

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 <jgross@xxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: boris.ostrovsky@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20180226140818.4849-1-jgross@xxxxxxxx
[bwh: Backported to 3.16:
 - Include <asm/cpufeature.h> instead of <asm/cpufeatures.h>
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c
@@ -1,10 +1,13 @@
 #include <linux/types.h>
 #include <linux/clockchips.h>
+#include <linux/percpu-defs.h>
 
 #include <xen/interface/xen.h>
 #include <xen/grant_table.h>
 #include <xen/events.h>
 
+#include <asm/cpufeature.h>
+#include <asm/msr-index.h>
 #include <asm/xen/hypercall.h>
 #include <asm/xen/page.h>
 #include <asm/fixmap.h>
@@ -12,6 +15,8 @@
 #include "xen-ops.h"
 #include "mmu.h"
 
+static DEFINE_PER_CPU(u64, spec_ctrl);
+
 static void xen_pv_pre_suspend(void)
 {
 	xen_mm_pin_all();
@@ -84,6 +89,9 @@ static void xen_vcpu_notify_restore(void
 {
 	unsigned long reason = (unsigned long)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;
@@ -93,6 +101,13 @@ static void xen_vcpu_notify_restore(void
 
 static void xen_vcpu_notify_suspend(void *data)
 {
+	u64 tmp;
+
+	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)