linux-kernel - Re: [patch 2/3] mmu_notifier: Callbacks to invalidate address ranges

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Message-ID: <Pine.LNX.4.64.0801311200250.25299@schroedinger.engr.sgi.com>
Date:	Thu, 31 Jan 2008 12:07:00 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	Robin Holt <holt@....com>, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 2/3] mmu_notifier: Callbacks to invalidate address ranges

On Thu, 31 Jan 2008, Andrea Arcangeli wrote:

> On Wed, Jan 30, 2008 at 08:57:52PM -0800, Christoph Lameter wrote:
> > @@ -211,7 +212,9 @@ asmlinkage long sys_remap_file_pages(uns
> >  		spin_unlock(&mapping->i_mmap_lock);
> >  	}
> >  
> > +	mmu_notifier(invalidate_range_begin, mm, start, start + size, 0);
> >  	err = populate_range(mm, vma, start, size, pgoff);
> > +	mmu_notifier(invalidate_range_end, mm, 0);
> >  	if (!err && !(flags & MAP_NONBLOCK)) {
> >  		if (unlikely(has_write_lock)) {
> >  			downgrade_write(&mm->mmap_sem);
> 
> This can't be enough for GRU, infact it can't work for KVM either. You
> got 1) to have some invalidate_page for GRU before freeing the page,
> and 2) to pass start, end to range_end (if you want kvm to use it
> instead of invalidate_page).

The external references are dropped when calling invalidate_range_begin. 
This would work both for the KVM and the GRU. Why would KVM not be able to 
invalidate the range before? Locking conventions is that no additional 
external reference can be added between invalidate_range_begin and 
invalidate_range_end. So KVM is fine too.

> mremap still missing as a whole.

mremap uses do_munmap which calls into unmap_region() that already has 
callbacks. So what is wrong there?
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