Re: [PATCH] x86/power: Fix 'nosmt' vs. hibernation triple fault during resume

[Rafael J. Wysocki]

On Tue, May 28, 2019 at 11:31 PM Jiri Kosina <jikos@xxxxxxxxxx> wrote:
>
> From: Jiri Kosina <jkosina@xxxxxxx>
>
> As explained in
>
>         0cc3cd21657b ("cpu/hotplug: Boot HT siblings at least once")
>
> we always, no matter what, have to bring up x86 HT siblings during boot at
> least once in order to avoid first MCE bringing the system to its knees.
>
> That means that whenever 'nosmt' is supplied on the kernel command-line,
> all the HT siblings are as a result sitting in mwait or cpudile after
> going through the online-offline cycle at least once.
>
> This causes a serious issue though when a kernel, which saw 'nosmt' on its
> commandline, is going to perform resume from hibernation: if the resume
> from the hibernated image is successful, cr3 is flipped in order to point
> to the address space of the kernel that is being resumed, which in turn
> means that all the HT siblings are all of a sudden mwaiting on address
> which is no longer valid.
>
> That results in triple fault shortly after cr3 is switched, and machine
> reboots.
>
> Fix this by always waking up all the SMT siblings before initiating the
> 'restore from hibernation' process; this guarantees that all the HT
> siblings will be properly carried over to the resumed kernel waiting in
> resume_play_dead(), and acted upon accordingly afterwards, based on the
> target kernel configuration.
>
> Cc: stable@xxxxxxxxxxxxxxx # v4.19+
> Debugged-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Fixes: 0cc3cd21657b ("cpu/hotplug: Boot HT siblings at least once")
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>

I can take this or, in case it is better to route it through x86:

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

> ---
>  arch/x86/power/cpu.c | 11 +++++++++++
>  include/linux/cpu.h  |  2 ++
>  kernel/cpu.c         |  2 +-
>  3 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
> index a7d966964c6f..bde8ce1f6c6c 100644
> --- a/arch/x86/power/cpu.c
> +++ b/arch/x86/power/cpu.c
> @@ -299,9 +299,20 @@ int hibernate_resume_nonboot_cpu_disable(void)
>          * address in its instruction pointer may not be possible to resolve
>          * any more at that point (the page tables used by it previously may
>          * have been overwritten by hibernate image data).
> +        *
> +        * First, make sure that we wake up all the potentially disabled SMT
> +        * threads which have been initially brought up and then put into
> +        * mwait/cpuidle sleep.
> +        * Those will be put to proper (not interfering with hibernation
> +        * resume) sleep afterwards, and the resumed kernel will decide itself
> +        * what to do with them.
>          */
>         smp_ops.play_dead = resume_play_dead;
> +       ret = cpuhp_smt_enable();
> +       if (ret)
> +               goto out;
>         ret = disable_nonboot_cpus();
> +out:
>         smp_ops.play_dead = play_dead;
>         return ret;
>  }
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 3813fe45effd..b5523552a607 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -201,10 +201,12 @@ enum cpuhp_smt_control {
>  extern enum cpuhp_smt_control cpu_smt_control;
>  extern void cpu_smt_disable(bool force);
>  extern void cpu_smt_check_topology(void);
> +extern int cpuhp_smt_enable(void);
>  #else
>  # define cpu_smt_control               (CPU_SMT_NOT_IMPLEMENTED)
>  static inline void cpu_smt_disable(bool force) { }
>  static inline void cpu_smt_check_topology(void) { }
> +static inline int cpuhp_smt_enable(void) { return 0; }
>  #endif
>
>  /*
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index f2ef10460698..3ff5ce0e4132 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -2093,7 +2093,7 @@ static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
>         return ret;
>  }
>
> -static int cpuhp_smt_enable(void)
> +int cpuhp_smt_enable(void)
>  {
>         int cpu, ret = 0;
>
>
> --
> Jiri Kosina
> SUSE Labs