Messages in this thread | | | Date | Fri, 25 Jan 2008 09:46:33 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/6] x86: fix NX bit handling in change_page_attr |
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* 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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