linux-kernel - [tip:x86/mm] x86/mm: Disable ioremap free page handling on x86-PAE

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Date:   Wed, 4 Jul 2018 12:39:52 -0700
From:   tip-bot for Toshi Kani <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, toshi.kani@....com, mhocko@...e.com,
        stable@...r.kernel.org, akpm@...ux-foundation.org,
        mingo@...nel.org, joro@...tes.org, tglx@...utronix.de,
        hpa@...or.com
Subject: [tip:x86/mm] x86/mm: Disable ioremap free page handling on x86-PAE

Commit-ID:  f967db0b9ed44ec3057a28f3b28efc51df51b835
Gitweb:     https://git.kernel.org/tip/f967db0b9ed44ec3057a28f3b28efc51df51b835
Author:     Toshi Kani <toshi.kani@....com>
AuthorDate: Wed, 27 Jun 2018 08:13:46 -0600
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 4 Jul 2018 21:37:08 +0200

x86/mm: Disable ioremap free page handling on x86-PAE

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@...tes.org>
Signed-off-by: Toshi Kani <toshi.kani@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: mhocko@...e.com
Cc: akpm@...ux-foundation.org
Cc: hpa@...or.com
Cc: cpandya@...eaurora.org
Cc: linux-mm@...ck.org
Cc: linux-arm-kernel@...ts.infradead.org
Cc: stable@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: <stable@...r.kernel.org>
Link: https://lkml.kernel.org/r/20180627141348.21777-2-toshi.kani@hpe.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 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 */