linux-kernel - Re: [PATCH 4/9] Vmi fix highpte

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Date:	Fri, 02 Mar 2007 23:17:10 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Chris Wright <chrisw@...s-sol.org>, Andi Kleen <ak@....de>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/9] Vmi fix highpte

Jeremy Fitzhardinge wrote:
> Those are bugs that can occur, but they don't apply in this case.  The
> vmi implementation of kmap_atomic_pte() would be:
>
> static void *vmi_kmap_atomic_pte(struct page *page, enum km_type type)
> {
> 	void *ptep = kmap_atomic(page, type);
> 	vmi_map_pt_hook(type, ptep, page_to_pfn(page));
> 	return ptep;
> }
>
> Right?  Which is functionally identical to the code in your patch,
> except wrapped up in a new function.
>   

Yes, but the hook point now happens before the page table mapping.  Not 
that it should cause a problem.  But we've been testing things the 
original way for over a year now, and if we want to get the fix upstream 
for 2.6.21, it seems better to upstream a more tested fix rather than a 
new way of doing things, even if it is identical in theory.

That said, I have no problems with the approach you propose going 
forward.  I just don't think it is appropriate for an -rc release, 
because it provides no tangible benefit for any of the in-kernel code, 
and causes a lot of retesting.  I still believe there is almost zero 
risk to doing things the way you propose.  But I am also a firm believer 
in shipping what is tested and working unless there is a compelling 
reason to do otherwise.  And if Xen is not going to be in 2.6.21, the 
compelling reason becomes getting the code working for both of us for 
2.6.22 - so let's do that, and keep the patches from Andrew's -mm tree 
around to make sure that we have a suitable patch base that can be 
applied to 2.6.21 for any distros that are willing to pick up the Xen 
paravirt-ops.

Sound reasonable?

Zach
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