From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: x86@xxxxxxxxxx Cc: Nadav Amit <namit@xxxxxxxxxx> --- 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); + + 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); + + /* * Copy the PMD. That is, the kernelmode and usermode * tables will share the last-level page tables of this * address range @@ -348,7 +360,7 @@ static void __init pti_clone_entry_text( { pti_clone_pmds((unsigned long) __entry_text_start, (unsigned long) __irqentry_text_end, - _PAGE_RW | _PAGE_GLOBAL); + _PAGE_RW); } /* _