linux-kernel - Re: [PATCH v4 2/2] powerpc/mm: Tracking vDSO remap

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Message-ID: <551538B5.2030507@linux.vnet.ibm.com>
Date:	Fri, 27 Mar 2015 12:02:13 +0100
From:	Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	Guan Xuetao <gxt@...c.pku.edu.cn>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net,
	user-mode-linux-user@...ts.sourceforge.net,
	linux-arch@...r.kernel.org, linux-mm@...ck.org, cov@...eaurora.org,
	criu@...nvz.org
Subject: Re: [PATCH v4 2/2] powerpc/mm: Tracking vDSO remap

On 26/03/2015 19:55, Ingo Molnar wrote:
> 
> * Laurent Dufour <ldufour@...ux.vnet.ibm.com> wrote:
> 
>> +{
>> +	unsigned long vdso_end, vdso_start;
>> +
>> +	if (!mm->context.vdso_base)
>> +		return;
>> +	vdso_start = mm->context.vdso_base;
>> +
>> +#ifdef CONFIG_PPC64
>> +	/* Calling is_32bit_task() implies that we are dealing with the
>> +	 * current process memory. If there is a call path where mm is not
>> +	 * owned by the current task, then we'll have need to store the
>> +	 * vDSO size in the mm->context.
>> +	 */
>> +	BUG_ON(current->mm != mm);
>> +	if (is_32bit_task())
>> +		vdso_end = vdso_start + (vdso32_pages << PAGE_SHIFT);
>> +	else
>> +		vdso_end = vdso_start + (vdso64_pages << PAGE_SHIFT);
>> +#else
>> +	vdso_end = vdso_start + (vdso32_pages << PAGE_SHIFT);
>> +#endif
>> +	vdso_end += (1<<PAGE_SHIFT); /* data page */
>> +
>> +	/* Check if the vDSO is in the range of the remapped area */
>> +	if ((vdso_start <= old_start && old_start < vdso_end) ||
>> +	    (vdso_start < old_end && old_end <= vdso_end)  ||
>> +	    (old_start <= vdso_start && vdso_start < old_end)) {
>> +		/* Update vdso_base if the vDSO is entirely moved. */
>> +		if (old_start == vdso_start && old_end == vdso_end &&
>> +		    (old_end - old_start) == (new_end - new_start))
>> +			mm->context.vdso_base = new_start;
>> +		else
>> +			mm->context.vdso_base = 0;
>> +	}
>> +}
> 
> Oh my, that really looks awfully complex, as you predicted, and right 
> in every mremap() call.

I do agree, that's awfully complex ;)

> I'm fine with your original, imperfect, KISS approach. Sorry about 
> this detour ...
>
> Reviewed-by: Ingo Molnar <mingo@...nel.org>

No problem, so let's stay on the v3 version of the patch.
Thanks for Reviewed-by statement which, I guess, applied to the v3 too.
Should I resend the v3 ?

Thanks,
Laurent.

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