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    SubjectRe: [PATCH 4.4 20/43] mm/vmalloc: add interfaces to free unmapped page table
    Date
    On Tue, 2018-03-27 at 15:17 -0500, Dan Rue wrote:
    > On Tue, Mar 27, 2018 at 06:27:24PM +0200, Greg Kroah-Hartman wrote:
    > > 4.4-stable review patch. If anyone has any objections, please let me know.
    > >
    > > ------------------
    > >
    > > From: Toshi Kani <toshi.kani@hpe.com>
    > >
    > > commit b6bdb7517c3d3f41f20e5c2948d6bc3f8897394e upstream.
    > >
    > > On architectures with CONFIG_HAVE_ARCH_HUGE_VMAP set, ioremap() may
    > > create pud/pmd mappings. A kernel panic was observed on arm64 systems
    > > with Cortex-A75 in the following steps as described by Hanjun Guo.
    > >
    > > 1. ioremap a 4K size, valid page table will build,
    > > 2. iounmap it, pte0 will set to 0;
    > > 3. ioremap the same address with 2M size, pgd/pmd is unchanged,
    > > then set the a new value for pmd;
    > > 4. pte0 is leaked;
    > > 5. CPU may meet exception because the old pmd is still in TLB,
    > > which will lead to kernel panic.
    > >
    > > This panic is not reproducible on x86. INVLPG, called from iounmap,
    > > purges all levels of entries associated with purged address on x86. x86
    > > still has memory leak.
    > >
    > > The patch changes the ioremap path to free unmapped page table(s) since
    > > doing so in the unmap path has the following issues:
    > >
    > > - The iounmap() path is shared with vunmap(). Since vmap() only
    > > supports pte mappings, making vunmap() to free a pte page is an
    > > overhead for regular vmap users as they do not need a pte page freed
    > > up.
    > >
    > > - Checking if all entries in a pte page are cleared in the unmap path
    > > is racy, and serializing this check is expensive.
    > >
    > > - The unmap path calls free_vmap_area_noflush() to do lazy TLB purges.
    > > Clearing a pud/pmd entry before the lazy TLB purges needs extra TLB
    > > purge.
    > >
    > > Add two interfaces, pud_free_pmd_page() and pmd_free_pte_page(), which
    > > clear a given pud/pmd entry and free up a page for the lower level
    > > entries.
    > >
    > > This patch implements their stub functions on x86 and arm64, which work
    > > as workaround.
    > >
    > > [akpm@linux-foundation.org: fix typo in pmd_free_pte_page() stub]
    > > Link: http://lkml.kernel.org/r/20180314180155.19492-2-toshi.kani@hpe.com
    > > Fixes: e61ce6ade404e ("mm: change ioremap to set up huge I/O mappings")
    > > Reported-by: Lei Li <lious.lilei@hisilicon.com>
    > > Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
    > > Cc: Catalin Marinas <catalin.marinas@arm.com>
    > > Cc: Wang Xuefeng <wxf.wang@hisilicon.com>
    > > Cc: Will Deacon <will.deacon@arm.com>
    > > Cc: Hanjun Guo <guohanjun@huawei.com>
    > > 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: Borislav Petkov <bp@suse.de>
    > > Cc: Matthew Wilcox <willy@infradead.org>
    > > Cc: Chintan Pandya <cpandya@codeaurora.org>
    > > Cc: <stable@vger.kernel.org>
    > > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    > > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    >
    > This patch causes the following build error on 4.4 arm64:
    >
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=build-arm64 defconfig
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=build-arm64
    >
    > CC arch/arm64/mm/mmu.o
    > ../arch/arm64/mm/mmu.c:701:5: error: redefinition of ‘pud_free_pmd_page’
    > int pud_free_pmd_page(pud_t *pud)
    > ^~~~~~~~~~~~~~~~~
    > In file included from ../arch/arm64/include/asm/pgtable.h:682:0,
    > from ../include/linux/mm.h:55,
    > from ../include/linux/mman.h:4,
    > from ../arch/arm64/mm/mmu.c:25:
    > ../include/asm-generic/pgtable.h:777:19: note: previous definition of ‘pud_free_pmd_page’ was here
    > static inline int pud_free_pmd_page(pud_t *pud)
    > ^~~~~~~~~~~~~~~~~
    > ../arch/arm64/mm/mmu.c:706:5: error: redefinition of ‘pmd_free_pte_page’
    > int pmd_free_pte_page(pmd_t *pmd)
    > ^~~~~~~~~~~~~~~~~
    > In file included from ../arch/arm64/include/asm/pgtable.h:682:0,
    > from ../include/linux/mm.h:55,
    > from ../include/linux/mman.h:4,
    > from ../arch/arm64/mm/mmu.c:25:
    > ../include/asm-generic/pgtable.h:781:19: note: previous definition of ‘pmd_free_pte_page’ was here
    > static inline int pmd_free_pte_page(pmd_t *pmd)
    > ^~~~~~~~~~~~~~~~~
    > make[2]: *** [../scripts/Makefile.build:270: arch/arm64/mm/mmu.o] Error 1
    > make[1]: *** [/home/drue/src/linux/4.4-rc/Makefile:969: arch/arm64/mm] Error 2
    > make[1]: Leaving directory '/home/drue/src/linux/4.4-rc/build-arm64'
    > make: *** [Makefile:152: sub-make] Error 2
    >
    >
    > >
    > > ---
    > > arch/arm64/mm/mmu.c | 10 ++++++++++
    > > arch/x86/mm/pgtable.c | 24 ++++++++++++++++++++++++
    > > include/asm-generic/pgtable.h | 10 ++++++++++
    > > lib/ioremap.c | 6 ++++--
    > > 4 files changed, 48 insertions(+), 2 deletions(-)
    > >
    > > --- a/arch/arm64/mm/mmu.c
    > > +++ b/arch/arm64/mm/mmu.c
    > > @@ -697,3 +697,13 @@ void *__init fixmap_remap_fdt(phys_addr_
    > >
    > > return dt_virt;
    > > }
    > > +
    > > +int pud_free_pmd_page(pud_t *pud)
    > > +{
    > > + return pud_none(*pud);
    > > +}
    > > +
    > > +int pmd_free_pte_page(pmd_t *pmd)
    > > +{
    > > + return pmd_none(*pmd);
    > > +}

    Sorry for the trouble. For 4.4, we need to simply drop the change in
    the arch/arm64/mm/mmu.c file since arm64 gets the funcs from
    include/asm-generic/pgtable.h.

    Thanks,
    -Toshi
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