[MODERATED] Re: [PATCH v5 14/27] MDSv5 3

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Jan 18, 2019 at 04:50:29PM -0800, speck for Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
> Subject:  mds: Force clear cpu on kernel preemption
> 
> When the kernel is preempted we need to force a cpu clear,
> because the preemption might happen before the code
> has a chance to set TIF_CPU_CLEAR later.
> 
> We cannot rely on kernel code setting the flag before
> touching sensitive data: the flag setting could
> be implicit, like in memzero_explicit, which is always
> called later.
> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Thank you!
> ---
>  kernel/sched/core.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a674c7db2f29..b04918e9115c 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -11,6 +11,8 @@
>  
>  #include <linux/kcov.h>
>  
> +#include <linux/clearcpu.h>
> +
>  #include <asm/switch_to.h>
>  #include <asm/tlb.h>
>  
> @@ -3619,6 +3621,13 @@ asmlinkage __visible void __sched notrace preempt_schedule(void)
>  	if (likely(!preemptible()))
>  		return;
>  
> +	/*
> +	 * For kernel preemption we need to force a cpu clear
> +	 * because it could happen before the code has a chance
> +	 * to set TIF_CLEAR_CPU.
> +	 */
> +	lazy_clear_cpu();
> +
>  	preempt_schedule_common();
>  }
>  NOKPROBE_SYMBOL(preempt_schedule);
> -- 
> 2.17.2