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

From: Ingo Molnar <[email-masked]>
Date: Thu, 26 Mar 2015 19:55:50 +0100

* 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'm fine with your original, imperfect, KISS approach. Sorry about 
this detour ...

Reviewed-by: Ingo Molnar <[email-masked]>

Thanks,

	Ingo