linux-kernel - Re: [PATCH V2] pv-grub: Fix for incorrect dom->p2m

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Message-ID: <20110426205809.GU4918@const.famille.thibault.fr>
Date:	Tue, 26 Apr 2011 22:58:09 +0200
From:	Samuel Thibault <samuel.thibault@...-lyon.org>
To:	Daniel Kiper <dkiper@...-space.pl>
Cc:	konrad.wilk@...cle.com, stefano.stabellini@...citrix.com,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] pv-grub: Fix for incorrect dom->p2m_host[] list initialization

Daniel Kiper, le Tue 26 Apr 2011 20:56:49 +0200, a écrit :
> New time optimized version.
> 
> After a lot of debugging and long reading of Linux Kernel and Xen code
> finally I killed deeply hidden bug in pv-grub. Details below.
> Additionally, I am CC'ing this e-mail to LKML because this issue
> looks like Linux Kernel problem, however, it is not.
> 
> This patch applies to Xen Ver. 4.0, Xen Ver. 4.1 and Xen unstable tree.
> 
> # HG changeset patch
> # User dkiper@...-space.pl
> # Date 1303843062 -7200
> # Node ID c4c2919afe9727e107ad3b862619b40d4731d3e4
> # Parent  dbf2ddf652dc3dd927447e79ef4bc586de55d708
> Introduction of Linux Kernel git commit ceefccc93932b920a8ec6f35f596db05202a12fe
> (x86: default CONFIG_PHYSICAL_START and CONFIG_PHYSICAL_ALIGN to 16 MB) revealed
> deeply hidden bug in pv-grub. During kernel load stage dom->p2m_host[] list has
> been incorrectly initialized.
> 
> At the beginning of kernel load stage dom->p2m_host[] list is populated with
> current PFN->MFN layout. Later during memory allocation (memory is allocated
> page by page in kexec_allocate()) page order is changed to establish linear
> layout in new domain. It is done by exchanging subsequent MFNs with newly
> allocated MFNs. dom->p2m_host[] list is indexed by currently requested PFN
> (it is incremented from 0) and PFN of newly allocated paged. If PFN of newly
> allocated page is less than currently requested PFN then earlier allocated
> MFN is overwritten which leads to domain crash later. This patch corrects
> that issue. If PFN of newly allocated page is less then currently requested
> PFN then relevant PFN/MFN pair is properly calculated and usual exchange
> occurs later.
> 
> Signed-off-by: Daniel Kiper <dkiper@...-space.pl>

Reviewed-by: Samuel Thibault <samuel.thibault@...-lyon.org>
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