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    Subject[PATCH 4.18 07/22] x86/mm: Disable ioremap free page handling on x86-PAE
    Date
    4.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

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

    commit f967db0b9ed44ec3057a28f3b28efc51df51b835 upstream.

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

    ---
    arch/x86/mm/pgtable.c | 19 +++++++++++++++++++
    1 file changed, 19 insertions(+)

    --- 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 */

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