On Tue, Jan 15, 2013 at 01:21:27PM +0000, Matt Wilson wrote: > Commit 85ff6acb075a484780b3d763fdf41596d8fc0970 (xen/granttable: Grant > tables V2 implementation) changed the GREFS_PER_GRANT_FRAME macro from > a constant to a conditional expression. The expression depends on > grant_table_version being appropriately set. Unfortunately, at init > time grant_table_version will be 0. The GREFS_PER_GRANT_FRAME > conditional expression checks for "grant_table_version == 1", and > therefore returns the number of grant references per frame for v2. > > This causes gnttab_init() to allocate fewer pages for gnttab_list, as > a frame can old half the number of v2 entries than v1 entries. After > gnttab_resume() is called, grant_table_version is appropriately > set. nr_init_grefs will then be miscalculated and gnttab_free_count > will hold a value larger than the actual number of free gref entries. > > If a guest is heavily utilizing improperly initialized v1 grant > tables, memory corruption can occur. One common manifestation is > corruption of the vmalloc list, resulting in a poisoned pointer > derefrence when accessing /proc/meminfo or /proc/vmallocinfo: > > [ 40.770064] BUG: unable to handle kernel paging request at 0000200200001407 > [ 40.770083] IP: [<ffffffff811a6fb0>] get_vmalloc_info+0x70/0x110 > [ 40.770102] PGD 0 > [ 40.770107] Oops: 0000 [#1] SMP > [ 40.770114] CPU 10 > > This patch introduces a static variable, grefs_per_grant_frame, to > cache the calculated value. gnttab_init() now calls > gnttab_request_version() early so that grant_table_version and > grefs_per_grant_frame can be appropriately set. A few BUG_ON()s have > been added to prevent this type of bug from reoccurring in the future. > > Signed-off-by: Matt Wilson <m...@amazon.com> > Reviewed-and-Tested-by: Steven Noonan <snoo...@amazon.com> > Signed-off-by: Ian Campbell <ian.campb...@citrix.com>
Correction, that should have been "Acked-by: Ian Campbell <ian.campb...@citrix.com>". My apologies. Matt > Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com> > Cc: Annie Li <annie...@oracle.com> > Cc: xen-de...@lists.xen.org > Cc: linux-kernel@vger.kernel.org > Cc: sta...@vger.kernel.org # v3.3 and newer -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
