linux-kernel - Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

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Date:	Tue, 29 Jan 2008 17:20:04 +0100
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Robin Holt <holt@....com>, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>, Nick Piggin <npiggin@...e.de>,
	kvm-devel@...ts.sourceforge.net,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address
	ranges

On Mon, Jan 28, 2008 at 12:28:42PM -0800, Christoph Lameter wrote:
> Index: linux-2.6/mm/fremap.c
> ===================================================================
> --- linux-2.6.orig/mm/fremap.c	2008-01-25 19:31:05.000000000 -0800
> +++ linux-2.6/mm/fremap.c	2008-01-25 19:32:49.000000000 -0800
> @@ -15,6 +15,7 @@
>  #include <linux/rmap.h>
>  #include <linux/module.h>
>  #include <linux/syscalls.h>
> +#include <linux/mmu_notifier.h>
>  
>  #include <asm/mmu_context.h>
>  #include <asm/cacheflush.h>
> @@ -211,6 +212,7 @@ asmlinkage long sys_remap_file_pages(uns
>  		spin_unlock(&mapping->i_mmap_lock);
>  	}
>  
> +	mmu_notifier(invalidate_range, mm, start, start + size, 0);
>  	err = populate_range(mm, vma, start, size, pgoff);

How can it be right to invalidate_range _before_ ptep_clear_flush?

> @@ -1634,6 +1639,8 @@ gotten:
>  	/*
>  	 * Re-check the pte - we dropped the lock
>  	 */
> +	mmu_notifier(invalidate_range, mm, address,
> +				address + PAGE_SIZE - 1, 0);
>  	page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
>  	if (likely(pte_same(*page_table, orig_pte))) {
>  		if (old_page) {

What's the point of invalidate_range when the size is PAGE_SIZE? And
how can it be right to invalidate_range _before_ ptep_clear_flush?
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