Re: [patch 20/24] x86/speculation: Split out TIF update

[Jiri Kosina]

On Tue, 27 Nov 2018, Jiri Kosina wrote:


> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -474,6 +474,21 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
>  
>  	tifn = READ_ONCE(task_thread_info(next_p)->flags);
>  	tifp = READ_ONCE(task_thread_info(prev_p)->flags);
> +
> +	/*
> +	 * SECCOMP tasks might have had their spec_ctrl flags updated during
> +	 * runtime from a different CPU.
> +	 *
> +	 * When switching to such a task, populate thread flags with the ones
> +	 * that have been temporarily saved in spec_flags by task_update_spec_tif()
> +	 * in order to make sure MSR value is always kept up to date.
> +	 *
> +	 * SECCOMP tasks never disable the mitigation for other threads, only enable.
> +	 */
> +	if (IS_ENABLED(CONFIG_SECCOMP) &&
> +			test_and_clear_tsk_thread_flag(next_p, TIF_SPEC_UPDATE))
> +		tifp |= READ_ONCE(task_thread_info(next_p)->spec_flags);

This should be 'tifn' of course.

-- 
Jiri Kosina
SUSE Labs