• Dave Hansen's avatar
    x86, mm: Make DEBUG_VIRTUAL work earlier in boot · a25b9316
    Dave Hansen authored
    The KVM code has some repeated bugs in it around use of __pa() on
    per-cpu data.  Those data are not in an area on which using
    __pa() is valid.  However, they are also called early enough in
    boot that __vmalloc_start_set is not set, and thus the
    CONFIG_DEBUG_VIRTUAL debugging does not catch them.
    
    This adds a check to also verify __pa() calls against max_low_pfn,
    which we can use earler in boot than is_vmalloc_addr().  However,
    if we are super-early in boot, max_low_pfn=0 and this will trip
    on every call, so also make sure that max_low_pfn is set before
    we try to use it.
    
    With this patch applied, CONFIG_DEBUG_VIRTUAL will actually
    catch the bug I was chasing (and fix later in this series).
    
    I'd love to find a generic way so that any __pa() call on percpu
    areas could do a BUG_ON(), but there don't appear to be any nice
    and easy ways to check if an address is a percpu one.  Anybody
    have ideas on a way to do this?
    Signed-off-by: default avatarDave Hansen <dave@linux.vnet.ibm.com>
    Link: http://lkml.kernel.org/r/20130122212430.F46F8159@kernel.stglabs.ibm.comSigned-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
    a25b9316
pat.c 20.9 KB