On Thu, Dec 16, 2021 at 05:13:47PM +0000, Christophe Leroy wrote:

Le 09/12/2021 à 11:02, Nicholas Piggin a écrit :

quoted

Excerpts from Christophe Leroy's message of December 9, 2021 3:18 am:

quoted

Use the generic version of arch_hugetlb_get_unmapped_area()
which is now available at all time.

Signed-off-by: Christophe Leroy <redacted>
---
  arch/powerpc/include/asm/book3s/64/hugetlb.h |  4 --
  arch/powerpc/mm/book3s64/radix_hugetlbpage.c | 55 --------------------
  arch/powerpc/mm/hugetlbpage.c                |  4 +-
  3 files changed, 1 insertion(+), 62 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/hugetlb.h b/arch/powerpc/include/asm/book3s/64/hugetlb.h
index 12e150e615b7..b37a28f62cf6 100644
--- a/arch/powerpc/include/asm/book3s/64/hugetlb.h
+++ b/arch/powerpc/include/asm/book3s/64/hugetlb.h

@@ -8,10 +8,6 @@
   */
  void radix__flush_hugetlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
  void radix__local_flush_hugetlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
-extern unsigned long
-radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
-				unsigned long len, unsigned long pgoff,
-				unsigned long flags);
  
  extern void radix__huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
  						unsigned long addr, pte_t *ptep,

diff --git a/arch/powerpc/mm/book3s64/radix_hugetlbpage.c b/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
index 23d3e08911d3..d2fb776febb4 100644
--- a/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
+++ b/arch/powerpc/mm/book3s64/radix_hugetlbpage.c

@@ -41,61 +41,6 @@ void radix__flush_hugetlb_tlb_range(struct vm_area_struct *vma, unsigned long st
  		radix__flush_tlb_range_psize(vma->vm_mm, start, end, psize);
  }
  
-/*
- * A vairant of hugetlb_get_unmapped_area doing topdown search
- * FIXME!! should we do as x86 does or non hugetlb area does ?
- * ie, use topdown or not based on mmap_is_legacy check ?
- */
-unsigned long
-radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
-				unsigned long len, unsigned long pgoff,
-				unsigned long flags)
-{
-	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
-	struct hstate *h = hstate_file(file);
-	int fixed = (flags & MAP_FIXED);
-	unsigned long high_limit;
-	struct vm_unmapped_area_info info;
-
-	high_limit = DEFAULT_MAP_WINDOW;
-	if (addr >= high_limit || (fixed && (addr + len > high_limit)))
-		high_limit = TASK_SIZE;

I wonder if generic hugetlb_get_unmapped_area needs to have the
arch_get_mmap_end() added.

arm64 has arch_get_mmap_end() and !HAVE_ARCH_HUGETLB_UNMAPPED_AREA so
it looks like it has broken large address hint logic for hugetlbfs
mappings? x86-64 defines their own and does the same hinting for
normal and hugetlbfs mmap.

If we had that and defied arch_get_mmap_end(), then this patch should
work.

As far as I can see, hugetlb_get_unmapped_area() variants used to be 
very similar to get_unmapped_area() until commit 1be7107fbe18 ("mm: 
larger stack guard gap, between vmas") and commit f6795053dac8 ("mm: 
mmap: Allow for "high" userspace addresses")

I see no reason why those changes couldn't apply to 
hugetlb_get_unmapped_area() as well.

Need to know what ARM64 think about it thought. Will, Catalin, any opinion ?

I think 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.

-- 
Catalin