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    Subject[PATCH 3.16 311/410] x86/xen: Zero MSR_IA32_SPEC_CTRL before suspend
    3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

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

    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: xen-devel@lists.xenproject.org
    Cc: boris.ostrovsky@oracle.com
    Link: https://lkml.kernel.org/r/20180226140818.4849-1-jgross@suse.com
    [bwh: Backported to 3.16:
    - Include <asm/cpufeature.h> instead of <asm/cpufeatures.h>
    - Adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- 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)
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