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commit 2992e545ea006992ec9dc91c4fa996ce1e15f921 upstream. Thomas Schlichter reported: > X.org uses libpciaccess which tries to mmap with write combining enabled via > /sys/bus/pci/devices/*/resource0_wc. Currently, when PAT is not enabled, the > kernel does fall back to uncached mmap. Then libpciaccess thinks it succeeded > mapping with write combining enabled and does not set up suited MTRR entries. > ;-( Instead of silently mapping pci mmap region as UC minus in the case of !pat_enabled and wc request, we can return error. Eric Anholt mentioned that caller (like X) typically follows up with UC minus pci mmap request and if there is a free mtrr slot, caller will manage adding WC mtrr. Jesse Barnes says: > Older versions of libpciaccess will behave better if we do it that way > (iirc it only allocates an MTRR if the resource_wc file doesn't exist or > fails to get mapped). Reported-by: Thomas Schlichter <thomas.schlichter@web.de> Signed-off-by: Thomas Schlichter <thomas.schlichter@web.de> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Acked-by: Eric Anholt <eric@anholt.net> Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>