[PATCH 3/8] x86/mm: Disable ioremap free page handling on x86-PAE

Andrea Righi andrea.righi at canonical.com
Fri Jun 14 08:55:01 UTC 2019


From: Toshi Kani <toshi.kani at hpe.com>

BugLink: https://bugs.launchpad.net/bugs/1830433

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 at 8bytes.org>
Signed-off-by: Toshi Kani <toshi.kani at hpe.com>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: mhocko at suse.com
Cc: akpm at linux-foundation.org
Cc: hpa at zytor.com
Cc: cpandya at codeaurora.org
Cc: linux-mm at kvack.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: stable at vger.kernel.org
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Michal Hocko <mhocko at suse.com>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: <stable at vger.kernel.org>
Link: https://lkml.kernel.org/r/20180627141348.21777-2-toshi.kani@hpe.com

(cherry picked from commit f967db0b9ed44ec3057a28f3b28efc51df51b835)
Tested-by: Connor Kuehl <connor.kuehl at canonical.com>
Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
---
 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 995dbab2aaef..ab199f7e7728 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -778,6 +778,7 @@ 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.
@@ -825,4 +826,22 @@ 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 */
-- 
2.20.1




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