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    SubjectRe: [PATCH 1/6] x86: fix NX bit handling in change_page_attr

    * Jeremy Fitzhardinge <jeremy@goop.org> wrote:

    > Huang, Ying wrote:

    >> This patch fixes a bug of change_page_attr/change_page_attr_addr on
    >> Intel i386/x86_64 CPUs. After changing page attribute to be
    >> executable with these functions, the page remains un-executable on
    >> Intel i386/x86_64 CPU. Because on Intel i386/x86_64 CPU, only if the
    >> "NX" bits of all three level page tables are cleared (PAE is
    >> enabled), the corresponding page is executable (refer to section
    >> 4.13.2 of Intel 64 and IA-32 Architectures Software Developer's
    >> Manual). So, the bug is fixed through clearing the "NX" bit of PMD
    >> when splitting the huge PMD.

    oops, nice detail!

    >> Signed-off-by: Huang Ying <ying.huang@intel.com>
    >>
    >> ---
    >> arch/x86/mm/pageattr.c | 1 +
    >> 1 file changed, 1 insertion(+)
    >>
    >> --- a/arch/x86/mm/pageattr.c
    >> +++ b/arch/x86/mm/pageattr.c
    >> @@ -124,6 +124,7 @@ static int split_large_page(pte_t *kpte,
    >> /*
    >> * Install the new, split up pagetable:
    >> */
    >> + pgprot_val(ref_prot) &= ~_PAGE_NX;
    >>
    >
    > I don't think its a good idea to treat pgprot_val() as an lvalue - it
    > precludes it from being turned into an inline function. I know there
    > are numerous other places which do, but we should avoid making it
    > worse.

    applied it with the following cleanup from Thomas:

    static int split_large_page(pte_t *kpte, unsigned long address)
    {
    - pgprot_t ref_prot = pte_pgprot(pte_clrhuge(*kpte));
    + pgprot_t ref_prot;
    ...
    + ref_prot = pte_pgprot(pte_mkexec(pte_clrhuge(*kpte)));

    i.e. it now goes through all the proper accessors.

    Ingo


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