Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux Dom0

[Roger Pau Monné <roger.pau%citrix.com@localhost>]

The following reply was made to PR port-xen/47057; it has been noted by GNATS.

From: =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= <roger.pau%citrix.com@localhost>
To: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
Cc: =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= <royger%NetBSD.org@localhost>,
        "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%NetBSD.org@localhost>,
        "port-xen-maintainer%netbsd.org@localhost" 
<port-xen-maintainer%NetBSD.org@localhost>,
        "gnats-admin%netbsd.org@localhost" <gnats-admin%NetBSD.org@localhost>, 
"netbsd-bugs%netbsd.org@localhost"
        <netbsd-bugs%NetBSD.org@localhost>
Subject: Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux
 Dom0
Date: Tue, 23 Oct 2012 16:01:06 +0200

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 Found the problem, grants from 0 to 8 (both included), shouldn't be
 used, they are reserved for the tools. I guess thats xenstore,
 xenconsole and friends, so that's where the corruption came from, and
 that's why the problem seemed to be related to xengnt_more_entries,
 because it gets called when those low grants are used. The attached
 patch solves the problem for me.
 
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        filename="0001-xen-don-t-use-grants-0-9.patch"
 
 From b80f10a3c3d0b95d3cd2a60a4669a2118fdbb9ef Mon Sep 17 00:00:00 2001
 From: Roger Pau Monne <roger.pau%citrix.com@localhost>
 Date: Tue, 23 Oct 2012 15:21:18 +0200
 Subject: [PATCH] xen: don't use grants 0-9
 
 Not all grants from the first frame can be used, grants from 0 to 8
 (both included) are reserved for external tools. Using this grants
 caused system crashes and fs corruption.
 ---
  sys/arch/xen/xen/xengnt.c |   15 +++++++++++----
  1 files changed, 11 insertions(+), 4 deletions(-)
 
 diff --git a/sys/arch/xen/xen/xengnt.c b/sys/arch/xen/xen/xengnt.c
 index 621d2dc..2de4fd3 100644
 --- a/sys/arch/xen/xen/xengnt.c
 +++ b/sys/arch/xen/xen/xengnt.c
 @@ -51,6 +51,9 @@ __KERNEL_RCSID(0, "$NetBSD: xengnt.c,v 1.24 2012/06/30 
23:36:20 jym Exp $");
  
  #define NR_GRANT_ENTRIES_PER_PAGE (PAGE_SIZE / sizeof(grant_entry_t))
  
 +/* External tools reserve first few grant table entries. */
 +#define NR_RESERVED_ENTRIES 8
 +
  /* Current number of frames making up the grant table */
  int gnt_nr_grant_frames;
  /* Maximum number of frames that can make up the grant table */
 @@ -161,7 +164,7 @@ xengnt_more_entries(void)
        gnttab_setup_table_t setup;
        u_long *pages;
        int nframes_new = gnt_nr_grant_frames + 1;
 -      int i;
 +      int i, start_gnt;
        KASSERT(mutex_owned(&grant_lock));
  
        if (gnt_nr_grant_frames == gnt_max_grant_frames)
 @@ -204,9 +207,13 @@ xengnt_more_entries(void)
  
        /*
         * add the grant entries associated to the last grant table frame
 -       * and mark them as free
 +       * and mark them as free. Prevent using the first grants (from 0 to 8)
 +       * since they are used by the tools.
         */
 -      for (i = gnt_nr_grant_frames * NR_GRANT_ENTRIES_PER_PAGE;
 +      start_gnt = (gnt_nr_grant_frames * NR_GRANT_ENTRIES_PER_PAGE) <
 +                              NR_RESERVED_ENTRIES + 1 ? NR_RESERVED_ENTRIES + 
1 :
 +                              (gnt_nr_grant_frames * 
NR_GRANT_ENTRIES_PER_PAGE);
 +      for (i = start_gnt;
            i < nframes_new * NR_GRANT_ENTRIES_PER_PAGE;
            i++) {
                KASSERT(gnt_entries[last_gnt_entry] == XENGNT_NO_ENTRY);
 @@ -240,7 +247,7 @@ xengnt_get_entry(void)
        last_gnt_entry--;
        entry = gnt_entries[last_gnt_entry];
        gnt_entries[last_gnt_entry] = XENGNT_NO_ENTRY;
 -      KASSERT(entry != XENGNT_NO_ENTRY);
 +      KASSERT(entry != XENGNT_NO_ENTRY && entry > NR_RESERVED_ENTRIES);
        KASSERT(last_gnt_entry >= 0);
        KASSERT(last_gnt_entry <= gnt_max_grant_frames * 
NR_GRANT_ENTRIES_PER_PAGE);
        return entry;
 -- 
 1.7.7.5 (Apple Git-26)
 
 
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