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    Subject[PATCH 09/11] x86/pti: enable global pages for shared areas
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    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 | 14 +++++++++++++-
    b/arch/x86/mm/pti.c | 23 ++++++++++++++++++++++-
    2 files changed, 35 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 2018-04-06 10:47:58.246796118 -0700
    +++ b/arch/x86/mm/cpu_entry_area.c 2018-04-06 10:47:58.252796118 -0700
    @@ -27,8 +27,20 @@ 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.
    + * _PAGE_GLOBAL gets reused to help indicate PROT_NONE for
    + * non-present PTEs, so be careful not to set it in that
    + * case to avoid confusion.
    + */
    + if (boot_cpu_has(X86_FEATURE_PGE) &&
    + (pgprot_val(flags) & _PAGE_PRESENT))
    + 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 2018-04-06 10:47:58.248796118 -0700
    +++ b/arch/x86/mm/pti.c 2018-04-06 10:47:58.252796118 -0700
    @@ -300,6 +300,27 @@ pti_clone_pmds(unsigned long start, unsi
    return;

    /*
    + * Only clone present PMDs. This ensures only setting
    + * _PAGE_GLOBAL on present PMDs. This should only be
    + * called on well-known addresses anyway, so a non-
    + * present PMD would be a surprise.
    + */
    + if (WARN_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT)))
    + 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 +369,7 @@ 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);
    }

    /*
    _
    \
     
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