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    Subject[PATCH v2 14/19] mm: Add vdso_base in mm_struct
    Date
    Instead of having every architecture to define vdso_base/vdso_addr etc,
    provide a generic mechanism to track vdso_base for landing in userspace.
    It'll minimize per-architecture difference, the number of callbacks to
    provide.

    Originally, it started from thread [1] where the need for .close()
    callback on vm_special_mapping was pointed, this generic code besides
    removing duplicated .mremap() callbacks provides a cheaper way to
    support munmap() on vdso mappings without introducing .close() callbacks
    for every architecture (with would bring even more code duplication).

    [1]: https://lore.kernel.org/linux-arch/CAJwJo6ZANqYkSHbQ+3b+Fi_VT80MtrzEV5yreQAWx-L8j8x2zA@mail.gmail.com/
    Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
    Cc: linux-mips@vger.kernel.org
    Signed-off-by: Dmitry Safonov <dima@arista.com>
    ---
    arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 3 ++-
    fs/aio.c | 3 ++-
    include/linux/mm.h | 3 ++-
    include/linux/mm_types.h | 10 ++++++++++
    mm/Kconfig | 3 +++
    mm/mmap.c | 19 ++++++++++++++++++-
    mm/mremap.c | 2 +-
    7 files changed, 38 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
    index e916646adc69..786c97203bf6 100644
    --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
    +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
    @@ -1458,7 +1458,8 @@ static int pseudo_lock_dev_release(struct inode *inode, struct file *filp)
    return 0;
    }

    -static int pseudo_lock_dev_mremap(struct vm_area_struct *area, unsigned long flags)
    +static int pseudo_lock_dev_mremap(struct vm_area_struct *old_vma,
    + struct vm_area_struct *new_vma, unsigned long flags)
    {
    /* Not supported */
    return -EINVAL;
    diff --git a/fs/aio.c b/fs/aio.c
    index d213be7b8a7e..9b205ebf17e8 100644
    --- a/fs/aio.c
    +++ b/fs/aio.c
    @@ -323,7 +323,8 @@ static void aio_free_ring(struct kioctx *ctx)
    }
    }

    -static int aio_ring_mremap(struct vm_area_struct *vma, unsigned long flags)
    +static int aio_ring_mremap(struct vm_area_struct *old_vma,
    + struct vm_area_struct *vma, unsigned long flags)
    {
    struct file *file = vma->vm_file;
    struct mm_struct *mm = vma->vm_mm;
    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index a1c25da94663..dbda1b91f971 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -559,7 +559,8 @@ struct vm_operations_struct {
    void (*close)(struct vm_area_struct * area);
    /* Called any time before splitting to check if it's allowed */
    int (*may_split)(struct vm_area_struct *area, unsigned long addr);
    - int (*mremap)(struct vm_area_struct *area, unsigned long flags);
    + int (*mremap)(struct vm_area_struct *old_vma,
    + struct vm_area_struct *new_vma, unsigned long flags);
    /*
    * Called by mprotect() to make driver-specific permission
    * checks before mprotect() is finalised. The VMA must not
    diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
    index 95a257927dae..e1ca750874af 100644
    --- a/include/linux/mm_types.h
    +++ b/include/linux/mm_types.h
    @@ -496,6 +496,16 @@ struct mm_struct {

    /* Architecture-specific MM context */
    mm_context_t context;
    +#ifdef CONFIG_ARCH_HAS_VDSO_BASE
    + /*
    + * Address of special mapping VMA to land after processing
    + * a signal. Reads are unprotected: if a thread unmaps or
    + * mremaps the mapping while another thread is processing
    + * a signal, it can segfault while landing.
    + */
    + void __user *vdso_base;
    +#endif
    +#define UNMAPPED_VDSO_BASE TASK_SIZE_MAX

    unsigned long flags; /* Must use atomic bitops to access */

    diff --git a/mm/Kconfig b/mm/Kconfig
    index 29904dc16bfc..941ae0597734 100644
    --- a/mm/Kconfig
    +++ b/mm/Kconfig
    @@ -893,4 +893,7 @@ config SECRETMEM
    select GENERIC_ALLOCATOR
    select CMA

    +config ARCH_HAS_VDSO_BASE
    + bool
    +
    endmenu
    diff --git a/mm/mmap.c b/mm/mmap.c
    index 17fe59a9780b..561afc3f1744 100644
    --- a/mm/mmap.c
    +++ b/mm/mmap.c
    @@ -3409,11 +3409,25 @@ void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)

    static vm_fault_t special_mapping_fault(struct vm_fault *vmf);

    +static void update_vdso_base(struct vm_area_struct *old_vma,
    + unsigned long new_addr)
    +{
    +#ifdef CONFIG_ARCH_HAS_VDSO_BASE
    + struct mm_struct *mm = old_vma->vm_mm;
    +
    + if (WARN_ON_ONCE(!mm))
    + return;
    + if (old_vma->vm_start == (unsigned long)mm->vdso_base)
    + mm->vdso_base = (void __user *)new_addr;
    +#endif
    +}
    +
    /*
    * Having a close hook prevents vma merging regardless of flags.
    */
    static void special_mapping_close(struct vm_area_struct *vma)
    {
    + update_vdso_base(vma, UNMAPPED_VDSO_BASE);
    }

    static const char *special_mapping_name(struct vm_area_struct *vma)
    @@ -3421,7 +3435,8 @@ static const char *special_mapping_name(struct vm_area_struct *vma)
    return ((struct vm_special_mapping *)vma->vm_private_data)->name;
    }

    -static int special_mapping_mremap(struct vm_area_struct *new_vma,
    +static int special_mapping_mremap(struct vm_area_struct *old_vma,
    + struct vm_area_struct *new_vma,
    unsigned long flags)
    {
    struct vm_special_mapping *sm = new_vma->vm_private_data;
    @@ -3435,6 +3450,8 @@ static int special_mapping_mremap(struct vm_area_struct *new_vma,
    if (sm->mremap)
    sm->mremap(sm, new_vma);

    + update_vdso_base(old_vma, new_vma->vm_start);
    +
    return 0;
    }

    diff --git a/mm/mremap.c b/mm/mremap.c
    index c5590afe7165..9595f6b72101 100644
    --- a/mm/mremap.c
    +++ b/mm/mremap.c
    @@ -543,7 +543,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
    if (moved_len < old_len) {
    err = -ENOMEM;
    } else if (vma->vm_ops && vma->vm_ops->mremap) {
    - err = vma->vm_ops->mremap(new_vma, flags);
    + err = vma->vm_ops->mremap(vma, new_vma, flags);
    }

    if (unlikely(err)) {
    --
    2.29.2
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