x86/pti: Enable global pages for shared areas

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: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180406205515.2977EE7D@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 35 insertions, 2 deletions

diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index 476d810639a8..b45f5aaefd74 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -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 --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 631507f0c198..8082f8b0c10e 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -300,6 +300,27 @@ pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
                         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(void)
 {
         pti_clone_pmds((unsigned long) __entry_text_start,
                         (unsigned long) __irqentry_text_end,
-                       _PAGE_RW | _PAGE_GLOBAL);
+                       _PAGE_RW);
 }
 
 /*