linux-kernel - Re: [PATCHv4 17/28] x86/vdso: Switch image on setns()/unshare()/clone()

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Date:   Fri, 14 Jun 2019 16:05:03 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dmitry Safonov <dima@...sta.com>
cc:     linux-kernel@...r.kernel.org, Adrian Reber <adrian@...as.de>,
        Andrei Vagin <avagin@...nvz.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jann Horn <jannh@...gle.com>, Jeff Dike <jdike@...toit.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        containers@...ts.linux-foundation.org, criu@...nvz.org,
        linux-api@...r.kernel.org, x86@...nel.org,
        Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCHv4 17/28] x86/vdso: Switch image on
 setns()/unshare()/clone()

On Wed, 12 Jun 2019, Dmitry Safonov wrote:
>  
> +#ifdef CONFIG_TIME_NS
> +int vdso_join_timens(struct task_struct *task)
> +{
> +	struct mm_struct *mm = task->mm;
> +	struct vm_area_struct *vma;
> +
> +	if (down_write_killable(&mm->mmap_sem))
> +		return -EINTR;
> +
> +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +		unsigned long size = vma->vm_end - vma->vm_start;
> +
> +		if (vma_is_special_mapping(vma, &vvar_mapping) ||
> +		    vma_is_special_mapping(vma, &vdso_mapping))
> +			zap_page_range(vma, vma->vm_start, size);
> +	}
> +
> +	up_write(&mm->mmap_sem);
> +	return 0;
> +}
> +#else /* CONFIG_TIME_NS */
> +int vdso_join_timens(struct task_struct *task)
> +{
> +	return -ENXIO;
> +}

Is that else path really required? The callsite is only compiled when
CONFIG_TIME_NS is enabled, right?

Thanks,

	tglx