Re: [PATCH v10 01/13] mm, hugetlbfs: Allow for "high" userspace addresses

Christophe Leroy
2022-05-03T16:30:04Z

Le 09/04/2022 à 19:17, Christophe Leroy a écrit :
> This is a complement of f6795053dac8 ("mm: mmap: Allow for "high"
> userspace addresses") for hugetlb.
>
> This patch adds support for "high" userspace addresses that are
> optionally supported on the system and have to be requested via a hint
> mechanism ("high" addr parameter to mmap).
>
> Architectures such as powerpc and x86 achieve this by making changes to
> their architectural versions of hugetlb_get_unmapped_area() function.
> However, arm64 uses the generic version of that function.
>
> So take into account arch_get_mmap_base() and arch_get_mmap_end() in
> hugetlb_get_unmapped_area(). To allow that, move those two macros
> out of mm/mmap.c into include/linux/sched/mm.h
>
> If these macros are not defined in architectural code then they default
> to (TASK_SIZE) and (base) so should not introduce any behavioural
> changes to architectures that do not define them.
>
> For the time being, only ARM64 is affected by this change.
>
> From Catalin (ARM64):
> We should have fixed hugetlb_get_unmapped_area() as well when we
> added support for 52-bit VA. The reason for commit f6795053dac8 was to
> prevent normal mmap() from returning addresses above 48-bit by default
> as some user-space had hard assumptions about this.
>
> It's a slight ABI change if you do this for hugetlb_get_unmapped_area()
> but I doubt anyone would notice. It's more likely that the current
> behaviour would cause issues, so I'd rather have them consistent.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Cc: Steve Capper <steve.capper@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Fixes: f6795053dac8 ("mm: mmap: Allow for "high" userspace addresses")
> Cc: <stable@vger.kernel.org> # 5.0.x
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Acked-by: Andrew Morton <akpm@linux-foundation.org>

This patch was merged in 5.18-rc4

See
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5f24d5a579d1eace79d505b148808a850b417d4c

The rest of the series is to be merged via powerpc tree.

> ---
> v10:
> - Moved as first patch of the series so that it can be applied
> separately as a flag and be easily applied back on stable.
> - Added text from Catalin explaining why it is a fixup.
> ---
> fs/hugetlbfs/inode.c | 9 +++++----
> include/linux/sched/mm.h | 8 ++++++++
> mm/mmap.c | 8 --------
> 3 files changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 99c7477cee5c..dd3a088db11d 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -206,7 +206,7 @@ hugetlb_get_unmapped_area_bottomup(struct file *file, unsigned long addr,
> info.flags = 0;
> info.length = len;
> info.low_limit = current->mm->mmap_base;
> - info.high_limit = TASK_SIZE;
> + info.high_limit = arch_get_mmap_end(addr);
> info.align_mask = PAGE_MASK & ~huge_page_mask(h);
> info.align_offset = 0;
> return vm_unmapped_area(&info);
> @@ -222,7 +222,7 @@ hugetlb_get_unmapped_area_topdown(struct file *file, unsigned long addr,
> info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> info.length = len;
> info.low_limit = max(PAGE_SIZE, mmap_min_addr);
> - info.high_limit = current->mm->mmap_base;
> + info.high_limit = arch_get_mmap_base(addr, current->mm->mmap_base);
> info.align_mask = PAGE_MASK & ~huge_page_mask(h);
> info.align_offset = 0;
> addr = vm_unmapped_area(&info);
> @@ -237,7 +237,7 @@ hugetlb_get_unmapped_area_topdown(struct file *file, unsigned long addr,
> VM_BUG_ON(addr != -ENOMEM);
> info.flags = 0;
> info.low_limit = current->mm->mmap_base;
> - info.high_limit = TASK_SIZE;
> + info.high_limit = arch_get_mmap_end(addr);
> addr = vm_unmapped_area(&info);
> }
>
> @@ -251,6 +251,7 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> struct hstate *h = hstate_file(file);
> + const unsigned long mmap_end = arch_get_mmap_end(addr);
>
> if (len & ~huge_page_mask(h))
> return -EINVAL;
> @@ -266,7 +267,7 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> if (addr) {
> addr = ALIGN(addr, huge_page_size(h));
> vma = find_vma(mm, addr);
> - if (TASK_SIZE - len >= addr &&
> + if (mmap_end - len >= addr &&
> (!vma || addr + len <= vm_start_gap(vma)))
> return addr;
> }
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index a80356e9dc69..1ad1f4bfa025 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -136,6 +136,14 @@ static inline void mm_update_next_owner(struct mm_struct *mm)
> #endif /* CONFIG_MEMCG */
>
> #ifdef CONFIG_MMU
> +#ifndef arch_get_mmap_end
> +#define arch_get_mmap_end(addr) (TASK_SIZE)
> +#endif
> +
> +#ifndef arch_get_mmap_base
> +#define arch_get_mmap_base(addr, base) (base)
> +#endif
> +
> extern void arch_pick_mmap_layout(struct mm_struct *mm,
> struct rlimit *rlim_stack);
> extern unsigned long
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 3aa839f81e63..313b57d55a63 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2117,14 +2117,6 @@ unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
> return addr;
> }
>
> -#ifndef arch_get_mmap_end
> -#define arch_get_mmap_end(addr) (TASK_SIZE)
> -#endif
> -
> -#ifndef arch_get_mmap_base
> -#define arch_get_mmap_base(addr, base) (base)
> -#endif
> -
> /* Get an address range which is currently unmapped.
> * For shmat() with addr=0.
> *