ioremap() supports pmd mappings on x86-PAE. However, kernel's pmd tables are not shared among processes on x86-PAE. Therefore, any update to sync'd pmd entries need re-syncing. Freeing a pte page also leads to a vmalloc fault and hits the BUG_ON in vmalloc_sync_one().
Disable free page handling on x86-PAE. pud_free_pmd_page() and pmd_free_pte_page() simply return 0 if a given pud/pmd entry is present. This assures that ioremap() does not update sync'd pmd entries at the cost of falling back to pte mappings.
Fixes: 28ee90fe6048 ("x86/mm: implement free pmd/pte page interfaces") Reported-by: Joerg Roedel joro@8bytes.org Signed-off-by: Toshi Kani toshi.kani@hpe.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Michal Hocko mhocko@suse.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@redhat.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Joerg Roedel joro@8bytes.org Cc: stable@vger.kernel.org --- arch/x86/mm/pgtable.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 47b5951e592b..1aeb7a5dbce5 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -719,6 +719,7 @@ int pmd_clear_huge(pmd_t *pmd) return 0; }
+#ifdef CONFIG_X86_64 /** * pud_free_pmd_page - Clear pud entry and free pmd page. * @pud: Pointer to a PUD. @@ -766,4 +767,22 @@ int pmd_free_pte_page(pmd_t *pmd)
return 1; } + +#else /* !CONFIG_X86_64 */ + +int pud_free_pmd_page(pud_t *pud) +{ + return pud_none(*pud); +} + +/* + * Disable free page handling on x86-PAE. This assures that ioremap() + * does not update sync'd pmd entries. See vmalloc_sync_one(). + */ +int pmd_free_pte_page(pmd_t *pmd) +{ + return pmd_none(*pmd); +} + +#endif /* CONFIG_X86_64 */ #endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */