This is a note to let you know that I've just added the patch titled

x86/xen: Zero MSR_IA32_SPEC_CTRL before suspend

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-xen-zero-msr_ia32_spec_ctrl-before-suspend.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 71c208dd54ab971036d83ff6d9837bae4976e623 Mon Sep 17 00:00:00 2001

From: Juergen Gross jgross@suse.com Date: Mon, 26 Feb 2018 15:08:18 +0100 Subject: x86/xen: Zero MSR_IA32_SPEC_CTRL before suspend

From: Juergen Gross jgross@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 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 Signed-off-by: Greg Kroah-Hartman gregkh@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 @@ -1,11 +1,14 @@ #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> @@ -68,6 +71,8 @@ static void xen_pv_post_suspend(int susp xen_mm_unpin_all(); }

+static DEFINE_PER_CPU(u64, spec_ctrl); + void xen_arch_pre_suspend(void) { if (xen_pv_domain()) @@ -84,6 +89,9 @@ 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; @@ -93,7 +101,15 @@ 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)

Patches currently in stable-queue which might be from jgross@suse.com are

queue-4.4/x86-xen-zero-msr_ia32_spec_ctrl-before-suspend.patch