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    Subject[ 12/27] x86, fpu: Avoid FPU lazy restore after suspend
    Date
    3.6-stable review patch.  If anyone has any objections, please let me know.

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

    From: Vincent Palatin <vpalatin@chromium.org>

    commit 644c154186386bb1fa6446bc5e037b9ed098db46 upstream.

    When a cpu enters S3 state, the FPU state is lost.
    After resuming for S3, if we try to lazy restore the FPU for a process running
    on the same CPU, this will result in a corrupted FPU context.

    Ensure that "fpu_owner_task" is properly invalided when (re-)initializing a CPU,
    so nobody will try to lazy restore a state which doesn't exist in the hardware.

    Tested with a 64-bit kernel on a 4-core Ivybridge CPU with eagerfpu=off,
    by doing thousands of suspend/resume cycles with 4 processes doing FPU
    operations running. Without the patch, a process is killed after a
    few hundreds cycles by a SIGFPE.

    Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
    Cc: Duncan Laurie <dlaurie@chromium.org>
    Cc: Olof Johansson <olofj@chromium.org>
    Link: http://lkml.kernel.org/r/1354306532-1014-1-git-send-email-vpalatin@chromium.org
    Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/include/asm/fpu-internal.h | 15 +++++++++------
    arch/x86/kernel/smpboot.c | 5 +++++
    2 files changed, 14 insertions(+), 6 deletions(-)

    --- a/arch/x86/include/asm/fpu-internal.h
    +++ b/arch/x86/include/asm/fpu-internal.h
    @@ -334,14 +334,17 @@ static inline void __thread_fpu_begin(st
    typedef struct { int preload; } fpu_switch_t;

    /*
    - * FIXME! We could do a totally lazy restore, but we need to
    - * add a per-cpu "this was the task that last touched the FPU
    - * on this CPU" variable, and the task needs to have a "I last
    - * touched the FPU on this CPU" and check them.
    + * Must be run with preemption disabled: this clears the fpu_owner_task,
    + * on this CPU.
    *
    - * We don't do that yet, so "fpu_lazy_restore()" always returns
    - * false, but some day..
    + * This will disable any lazy FPU state restore of the current FPU state,
    + * but if the current thread owns the FPU, it will still be saved by.
    */
    +static inline void __cpu_disable_lazy_restore(unsigned int cpu)
    +{
    + per_cpu(fpu_owner_task, cpu) = NULL;
    +}
    +
    static inline int fpu_lazy_restore(struct task_struct *new, unsigned int cpu)
    {
    return new == this_cpu_read_stable(fpu_owner_task) &&
    --- a/arch/x86/kernel/smpboot.c
    +++ b/arch/x86/kernel/smpboot.c
    @@ -68,6 +68,8 @@
    #include <asm/mwait.h>
    #include <asm/apic.h>
    #include <asm/io_apic.h>
    +#include <asm/i387.h>
    +#include <asm/fpu-internal.h>
    #include <asm/setup.h>
    #include <asm/uv/uv.h>
    #include <linux/mc146818rtc.h>
    @@ -817,6 +819,9 @@ int __cpuinit native_cpu_up(unsigned int

    per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;

    + /* the FPU context is blank, nobody can own it */
    + __cpu_disable_lazy_restore(cpu);
    +
    err = do_boot_cpu(apicid, cpu, tidle);
    if (err) {
    pr_debug("do_boot_cpu failed %d\n", err);



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