• Dave Hansen's avatar
    x86/mm: Comment _PAGE_GLOBAL mystery · 430d4005
    Dave Hansen authored
    I was mystified as to where the _PAGE_GLOBAL in the kernel page tables
    for kernel text came from.  I audited all the places I could find, but
    I missed one: head_64.S.
    
    The page tables that we create in here live for a long time, and they
    also have _PAGE_GLOBAL set, despite whether the processor supports it
    or not.  It's harmless, and we got *lucky* that the pageattr code
    accidentally clears it when we wipe it out of __supported_pte_mask and
    then later try to mark kernel text read-only.
    
    Comment some of these properties to make it easier to find and
    understand in the future.
    Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: David Woodhouse <dwmw2@infradead.org>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Kees Cook <keescook@google.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Nadav Amit <namit@vmware.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-mm@kvack.org
    Link: http://lkml.kernel.org/r/20180406205513.079BB265@viggo.jf.intel.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    430d4005
head_64.S 12.8 KB