Messages in this thread |  | | From | Nadav Amit <> | Subject | Re: [PATCH 09/11] x86/pti: enable global pages for shared areas | Date | Wed, 4 Apr 2018 04:45:00 +0000 |
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Dave Hansen <dave.hansen@linux.intel.com> wrote:
> > From: Dave Hansen <dave.hansen@linux.intel.com> > > The entry/exit text and cpu_entry_area are mapped into userspace and > the kernel. But, they are not _PAGE_GLOBAL. This creates unnecessary > TLB misses. > > Add the _PAGE_GLOBAL flag for these areas. > > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Andrea Arcangeli <aarcange@redhat.com> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Kees Cook <keescook@google.com> > Cc: Hugh Dickins <hughd@google.com> > Cc: Juergen Gross <jgross@suse.com> > Cc: x86@kernel.org > Cc: Nadav Amit <namit@vmware.com> > --- > > b/arch/x86/mm/cpu_entry_area.c | 10 +++++++++- > b/arch/x86/mm/pti.c | 14 +++++++++++++- > 2 files changed, 22 insertions(+), 2 deletions(-) > > diff -puN arch/x86/mm/cpu_entry_area.c~kpti-why-no-global arch/x86/mm/cpu_entry_area.c > --- a/arch/x86/mm/cpu_entry_area.c~kpti-why-no-global 2018-04-02 16:41:17.157605167 -0700 > +++ b/arch/x86/mm/cpu_entry_area.c 2018-04-02 16:41:17.162605167 -0700 > @@ -27,8 +27,16 @@ EXPORT_SYMBOL(get_cpu_entry_area); > void cea_set_pte(void *cea_vaddr, phys_addr_t pa, pgprot_t flags) > { > unsigned long va = (unsigned long) cea_vaddr; > + pte_t pte = pfn_pte(pa >> PAGE_SHIFT, flags); > > - set_pte_vaddr(va, pfn_pte(pa >> PAGE_SHIFT, flags)); > + /* > + * The cpu_entry_area is shared between the user and kernel > + * page tables. All of its ptes can safely be global. > + */ > + if (boot_cpu_has(X86_FEATURE_PGE)) > + pte = pte_set_flags(pte, _PAGE_GLOBAL);
I think it would be safer to check that the PTE is indeed present before setting _PAGE_GLOBAL. For example, percpu_setup_debug_store() sets PAGE_NONE for non-present entries. In this case, since PAGE_NONE and PAGE_GLOBAL use the same bit, everything would be fine, but it might cause bugs one day.
> + > + set_pte_vaddr(va, pte); > } > > static void __init > diff -puN arch/x86/mm/pti.c~kpti-why-no-global arch/x86/mm/pti.c > --- a/arch/x86/mm/pti.c~kpti-why-no-global 2018-04-02 16:41:17.159605167 -0700 > +++ b/arch/x86/mm/pti.c 2018-04-02 16:41:17.163605167 -0700 > @@ -300,6 +300,18 @@ pti_clone_pmds(unsigned long start, unsi > return; > > /* > + * Setting 'target_pmd' below creates a mapping in both > + * the user and kernel page tables. It is effectively > + * global, so set it as global in both copies. Note: > + * the X86_FEATURE_PGE check is not _required_ because > + * the CPU ignores _PAGE_GLOBAL when PGE is not > + * supported. The check keeps consistentency with > + * code that only set this bit when supported. > + */ > + if (boot_cpu_has(X86_FEATURE_PGE)) > + *pmd = pmd_set_flags(*pmd, _PAGE_GLOBAL);
Same here.
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