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    SubjectRe: [PATCH 4.4 20/43] mm/vmalloc: add interfaces to free unmapped page table
    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);
    > +}
    > --- a/arch/x86/mm/pgtable.c
    > +++ b/arch/x86/mm/pgtable.c
    > @@ -666,4 +666,28 @@ int pmd_clear_huge(pmd_t *pmd)
    >
    > return 0;
    > }
    > +
    > +/**
    > + * pud_free_pmd_page - Clear pud entry and free pmd page.
    > + * @pud: Pointer to a PUD.
    > + *
    > + * Context: The pud range has been unmaped and TLB purged.
    > + * Return: 1 if clearing the entry succeeded. 0 otherwise.
    > + */
    > +int pud_free_pmd_page(pud_t *pud)
    > +{
    > + return pud_none(*pud);
    > +}
    > +
    > +/**
    > + * pmd_free_pte_page - Clear pmd entry and free pte page.
    > + * @pmd: Pointer to a PMD.
    > + *
    > + * Context: The pmd range has been unmaped and TLB purged.
    > + * Return: 1 if clearing the entry succeeded. 0 otherwise.
    > + */
    > +int pmd_free_pte_page(pmd_t *pmd)
    > +{
    > + return pmd_none(*pmd);
    > +}
    > #endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
    > --- a/include/asm-generic/pgtable.h
    > +++ b/include/asm-generic/pgtable.h
    > @@ -755,6 +755,8 @@ int pud_set_huge(pud_t *pud, phys_addr_t
    > int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot);
    > int pud_clear_huge(pud_t *pud);
    > int pmd_clear_huge(pmd_t *pmd);
    > +int pud_free_pmd_page(pud_t *pud);
    > +int pmd_free_pte_page(pmd_t *pmd);
    > #else /* !CONFIG_HAVE_ARCH_HUGE_VMAP */
    > static inline int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
    > {
    > @@ -772,6 +774,14 @@ static inline int pmd_clear_huge(pmd_t *
    > {
    > return 0;
    > }
    > +static inline int pud_free_pmd_page(pud_t *pud)
    > +{
    > + return 0;
    > +}
    > +static inline int pmd_free_pte_page(pmd_t *pmd)
    > +{
    > + return 0;
    > +}
    > #endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
    >
    > #endif /* !__ASSEMBLY__ */
    > --- a/lib/ioremap.c
    > +++ b/lib/ioremap.c
    > @@ -83,7 +83,8 @@ static inline int ioremap_pmd_range(pud_
    >
    > if (ioremap_pmd_enabled() &&
    > ((next - addr) == PMD_SIZE) &&
    > - IS_ALIGNED(phys_addr + addr, PMD_SIZE)) {
    > + IS_ALIGNED(phys_addr + addr, PMD_SIZE) &&
    > + pmd_free_pte_page(pmd)) {
    > if (pmd_set_huge(pmd, phys_addr + addr, prot))
    > continue;
    > }
    > @@ -109,7 +110,8 @@ static inline int ioremap_pud_range(pgd_
    >
    > if (ioremap_pud_enabled() &&
    > ((next - addr) == PUD_SIZE) &&
    > - IS_ALIGNED(phys_addr + addr, PUD_SIZE)) {
    > + IS_ALIGNED(phys_addr + addr, PUD_SIZE) &&
    > + pud_free_pmd_page(pud)) {
    > if (pud_set_huge(pud, phys_addr + addr, prot))
    > continue;
    > }
    >
    >

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