Right now pgd_alloc() uses pgd_ctor(), which copies over the
current swapper_pg_dir[] to a new task's PGD.
This is not necessary, it's enough if we clear it: the PGD will
then be properly updated by arch_pgd_init_late().
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Waiman Long <Waiman.Long@xxxxxx>
Cc: linux-mm@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/mm/pgtable.c | 27 +++++++++------------------
1 file changed, 9 insertions(+), 18 deletions(-)
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 7cca42c01677..d7d341e57e33 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -87,20 +87,6 @@ void ___pud_free_tlb(struct mmu_gather *tlb, pud_t *pud)
#define UNSHARED_PTRS_PER_PGD \
(SHARED_KERNEL_PMD ? KERNEL_PGD_BOUNDARY : PTRS_PER_PGD)
-static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
-{
- /* If the pgd points to a shared pagetable level (either the
- ptes in non-PAE, or shared PMD in PAE), then just copy the
- references from swapper_pg_dir. */
- if (CONFIG_PGTABLE_LEVELS == 2 ||
- (CONFIG_PGTABLE_LEVELS == 3 && SHARED_KERNEL_PMD) ||
- CONFIG_PGTABLE_LEVELS == 4) {
- clone_pgd_range(pgd + KERNEL_PGD_BOUNDARY,
- swapper_pg_dir + KERNEL_PGD_BOUNDARY,
- KERNEL_PGD_PTRS);
- }
-}
-
/*
* List of all pgd's needed for non-PAE so it can invalidate entries
* in both cached and uncached pgd's; not needed for PAE since the
@@ -328,11 +314,16 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
goto out_free_pmds;
/*
- * No locking is needed here, as the PGD is still private,
- * so no code walking the task list and looking at mm->pgd
- * will be able to see it before it's fully constructed:
+ * Zero out the kernel portion here, we'll set them up in
+ * arch_pgd_init_late(), when the pgd is globally
+ * visible already per the task list, so that it cannot
+ * miss updates.
+ *
+ * We need to zero it here, to make sure arch_pgd_init_late()
+ * can initialize them without locking.
*/
- pgd_ctor(mm, pgd);
+ memset(pgd + KERNEL_PGD_BOUNDARY, 0, KERNEL_PGD_PTRS*sizeof(pgd_t));
+
pgd_prepopulate_pmd(mm, pgd, pmds);
return pgd;
--
2.1.4
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