Subject: Re: [PATCH v4 2/2] powerpc/mm: Tracking vDSO remap

From: Laurent Dufour <[email-masked]>
Date: Fri, 27 Mar 2015 12:02:13 +0100

On 26/03/2015 19:55, Ingo Molnar wrote:
> 
> * Laurent Dufour <[email-masked]> 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 <[email-masked]>

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.