linux-kernel - Re: [Xen-devel] [PATCH REPOST] pv-grub: Fix for incorrect dom->p2m

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Message-ID: <20110426142535.GA27417@router-fw-old.local.net-space.pl>
Date:	Tue, 26 Apr 2011 16:25:35 +0200
From:	Daniel Kiper <dkiper@...-space.pl>
To:	Samuel Thibault <samuel.thibault@...-lyon.org>
Cc:	Daniel Kiper <dkiper@...-space.pl>, konrad.wilk@...cle.com,
	stefano.stabellini@...citrix.com, xen-devel@...ts.xensource.com,
	linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH REPOST] pv-grub: Fix for incorrect dom->p2m_host[] list initialization

On Sat, Apr 23, 2011 at 12:33:32AM +0200, Samuel Thibault wrote:
> Hello,
>
> Daniel Kiper, le Fri 22 Apr 2011 23:25:45 +0200, a ?crit :
> > If pfn of newly allocated page is less than currently requested pfn
> > then relevant earlier allocated mfn is overwritten which leads to
> > domain crash later.
>
> Oops, good catch! And unfortunately it happens seldomly... I guess it
> may be the culprit for a fair number of other issues.

I discovered that issue on domU i386. It does not affect x86_64
in my environment. However, as you stated above that issue in some
circumstances could lead to mysterious system crashes or data
corruptions.

> > +	if (new_pfn < i)
> > +		for (new_pfn = i; new_pfn < dom->total_pages; ++new_pfn)
> > +			if (dom->p2m_host[new_pfn] == new_mfn)
> > +				break;
>
> Instead of looking for the page, which takes a linear time for each page
> and thus potentially quadratic time, we should probably rather record
> which PFN the MFNs < allocated have been moved to?

I am going to post new time optimized version
of that patch today or tommorow.

Daniel
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