From mboxrd@z Thu Jan  1 00:00:00 1970
From: George Dunlap <dunlapg@umich.edu>
Subject: Re: [PATCH 1 of 4] xentrace: reduce trace buffer size to
	something mfn_offset can reach
Date: Thu, 26 May 2011 11:05:14 +0100
Message-ID: <BANLkTinfAJZgDgiM9wzhuGR+c0eOa4mcYA@mail.gmail.com>
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To: Olaf Hering <olaf@aepfle.de>
Cc: xen-devel@lists.xensource.com, George Dunlap <george.dunlap@citrix.com>
List-Id: xen-devel@lists.xenproject.org

Acked-by: George Dunlap <george.dunlap@eu.citrix.com>

Sorry for the delay!
 -George

On Tue, May 10, 2011 at 3:32 PM, Olaf Hering <olaf@aepfle.de> wrote:
> # HG changeset patch
> # User Olaf Hering <olaf@aepfle.de>
> # Date 1305037380 -7200
> # Node ID 8ac937fa527b28243227193bf4749feb3a234c2c
> # Parent =A019452acd23045f40c4e18437f0a60f016757e5bd
> xentrace: reduce trace buffer size to something mfn_offset can reach
>
> The start of the array which holds the list of mfns for each cpus
> tracebuffer is stored in an unsigned short. This limits the total amount
> of pages for each cpu as the number of active cpus increases.
>
> Update the math in calculate_tbuf_size() to apply also this rule to the
> max number of trace pages. Without this change the index can overflow.
>
> Signed-off-by: Olaf Hering <olaf@aepfle.de>
>
> diff -r 19452acd2304 -r 8ac937fa527b xen/common/trace.c
> --- a/xen/common/trace.c =A0 =A0 =A0 =A0Fri May 06 11:15:35 2011 +0100
> +++ b/xen/common/trace.c =A0 =A0 =A0 =A0Tue May 10 16:23:00 2011 +0200
> @@ -112,11 +112,14 @@ static int calculate_tbuf_size(unsigned
> =A0 =A0 typeof(dummy_size.prod) max_size;
> =A0 =A0 struct t_info dummy_pages;
> =A0 =A0 typeof(dummy_pages.tbuf_size) max_pages;
> + =A0 =A0typeof(dummy_pages.mfn_offset[0]) max_mfn_offset;
> + =A0 =A0unsigned int max_cpus =3D num_online_cpus();
> =A0 =A0 unsigned int t_info_words;
>
> =A0 =A0 /* force maximum value for an unsigned type */
> =A0 =A0 max_size =3D -1;
> =A0 =A0 max_pages =3D -1;
> + =A0 =A0max_mfn_offset =3D -1;
>
> =A0 =A0 /* max size holds up to n pages */
> =A0 =A0 max_size /=3D PAGE_SIZE;
> @@ -124,6 +127,18 @@ static int calculate_tbuf_size(unsigned
> =A0 =A0 if ( max_size < max_pages )
> =A0 =A0 =A0 =A0 max_pages =3D max_size;
>
> + =A0 =A0/*
> + =A0 =A0 * max mfn_offset holds up to n pages per cpu
> + =A0 =A0 * The array of mfns for the highest cpu can start at the maximu=
m value
> + =A0 =A0 * mfn_offset can hold. So reduce the number of cpus and also th=
e mfn_offset.
> + =A0 =A0 */
> + =A0 =A0max_mfn_offset -=3D t_info_first_offset - 1;
> + =A0 =A0max_cpus--;
> + =A0 =A0if ( max_cpus )
> + =A0 =A0 =A0 =A0max_mfn_offset /=3D max_cpus;
> + =A0 =A0if ( max_mfn_offset < max_pages )
> + =A0 =A0 =A0 =A0max_pages =3D max_mfn_offset;
> +
> =A0 =A0 if ( pages > max_pages )
> =A0 =A0 {
> =A0 =A0 =A0 =A0 printk(XENLOG_INFO "xentrace: requested number of %u page=
s "
>
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