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

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Message-ID: <YIJwQ4brDIbKKiyZ@gmail.com>
Date:   Thu, 22 Apr 2021 23:59:15 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Oleg Nesterov <oleg@...hat.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 Wed, Apr 14, 2021 at 07:09:15PM +0200, Oleg Nesterov wrote:
> 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...

I agree.

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

No, it doesn't. It is leftover of unuse_mm. BTW why do we pass mm to kthread_unuse_mm?

Thanks,
Andrei.