linux-kernel - Re: [PATCH 2/4] arch/x86: implement the process_vm

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Date:   Wed, 14 Apr 2021 19:09:15 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrei Vagin <avagin@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-um@...ts.infradead.org, criu@...nvz.org, avagin@...gle.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Jeff Dike <jdike@...toit.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Weinberger <richard@....at>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/4] arch/x86: implement the process_vm_exec syscall

On 04/13, Andrei Vagin wrote:
>
> +static void swap_mm(struct mm_struct *prev_mm, struct mm_struct *target_mm)
> +{
> +	struct task_struct *tsk = current;
> +	struct mm_struct *active_mm;
> +
> +	task_lock(tsk);
> +	/* Hold off tlb flush IPIs while switching mm's */
> +	local_irq_disable();
> +
> +	sync_mm_rss(prev_mm);
> +
> +	vmacache_flush(tsk);
> +
> +	active_mm = tsk->active_mm;
> +	if (active_mm != target_mm) {
> +		mmgrab(target_mm);
> +		tsk->active_mm = target_mm;
> +	}
> +	tsk->mm = target_mm;
> +	switch_mm_irqs_off(active_mm, target_mm, tsk);
> +	local_irq_enable();
> +	task_unlock(tsk);
> +#ifdef finish_arch_post_lock_switch
> +	finish_arch_post_lock_switch();
> +#endif
> +
> +	if (active_mm != target_mm)
> +		mmdrop(active_mm);
> +}

I think this should be unified with kthread_use_mm() somehow...

And does it really need the "prev_mm" argument? It must be tsk->mm, no?

Oleg.