• Konrad Rzeszutek Wilk's avatar
    xen/pat: Disable PAT using pat_enabled value. · c79c4982
    Konrad Rzeszutek Wilk authored
    The git commit 8eaffa67
    (xen/pat: Disable PAT support for now) explains in details why
    we want to disable PAT for right now. However that
    change was not enough and we should have also disabled
    the pat_enabled value. Otherwise we end up with:
    
    mmap-example:3481 map pfn expected mapping type write-back for
    [mem 0x00010000-0x00010fff], got uncached-minus
     ------------[ cut here ]------------
    WARNING: at /build/buildd/linux-3.8.0/arch/x86/mm/pat.c:774 untrack_pfn+0xb8/0xd0()
    mem 0x00010000-0x00010fff], got uncached-minus
    ------------[ cut here ]------------
    WARNING: at /build/buildd/linux-3.8.0/arch/x86/mm/pat.c:774
    untrack_pfn+0xb8/0xd0()
    ...
    Pid: 3481, comm: mmap-example Tainted: GF 3.8.0-6-generic #13-Ubuntu
    Call Trace:
     [<ffffffff8105879f>] warn_slowpath_common+0x7f/0xc0
     [<ffffffff810587fa>] warn_slowpath_null+0x1a/0x20
     [<ffffffff8104bcc8>] untrack_pfn+0xb8/0xd0
     [<ffffffff81156c1c>] unmap_single_vma+0xac/0x100
     [<ffffffff81157459>] unmap_vmas+0x49/0x90
     [<ffffffff8115f808>] exit_mmap+0x98/0x170
     [<ffffffff810559a4>] mmput+0x64/0x100
     [<ffffffff810560f5>] dup_mm+0x445/0x660
     [<ffffffff81056d9f>] copy_process.part.22+0xa5f/0x1510
     [<ffffffff81057931>] do_fork+0x91/0x350
     [<ffffffff81057c76>] sys_clone+0x16/0x20
     [<ffffffff816ccbf9>] stub_clone+0x69/0x90
     [<ffffffff816cc89d>] ? system_call_fastpath+0x1a/0x1f
    ---[ end trace 4918cdd0a4c9fea4 ]---
    
    (a similar message shows up if you end up launching 'mcelog')
    
    The call chain is (as analyzed by Liu, Jinsong):
    do_fork
      --> copy_process
        --> dup_mm
          --> dup_mmap
           	--> copy_page_range
              --> track_pfn_copy
                --> reserve_pfn_range
                  --> line 624: flags != want_flags
    It comes from different memory types of page table (_PAGE_CACHE_WB) and MTRR
    (_PAGE_CACHE_UC_MINUS).
    
    Stefan Bader dug in this deep and found out that:
    "That makes it clearer as this will do
    
    reserve_memtype(...)
    --> pat_x_mtrr_type
      --> mtrr_type_lookup
        --> __mtrr_type_lookup
    
    And that can return -1/0xff in case of MTRR not being enabled/initialized. Which
    is not the case (given there are no messages for it in dmesg). This is not equal
    to MTRR_TYPE_WRBACK and thus becomes _PAGE_CACHE_UC_MINUS.
    
    It looks like the problem starts early in reserve_memtype:
    
           	if (!pat_enabled) {
                    /* This is identical to page table setting without PAT */
                    if (new_type) {
                            if (req_type == _PAGE_CACHE_WC)
                                    *new_type = _PAGE_CACHE_UC_MINUS;
                            else
                                   	*new_type = req_type & _PAGE_CACHE_MASK;
                   	}
                    return 0;
            }
    
    This would be what we want, that is clearing the PWT and PCD flags from the
    supported flags - if pat_enabled is disabled."
    
    This patch does that - disabling PAT.
    
    CC: stable@vger.kernel.org # 3.3 and further
    Reported-by: default avatarSander Eikelenboom <linux@eikelenboom.it>
    Reported-and-Tested-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Reported-and-Tested-by: default avatarStefan Bader <stefan.bader@canonical.com>
    Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    c79c4982
enlighten.c 38.8 KB