Subject: Re: [PATCH 2/2] powerpc: split hugepage when using subpage protection

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Fri, 17 May 2013 14:06:36 +0530

"Aneesh Kumar K.V" <[email-masked]> writes:

> From: "Aneesh Kumar K.V" <[email-masked]>
>
> We find all the overlapping vma and mark them such that we don't allocate
> hugepage in that range. Also we split existing huge page so that the
> normal page hash can be invalidated and new page faulted in with new
> protection bits.
>
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> ---
>  arch/powerpc/mm/subpage-prot.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/arch/powerpc/mm/subpage-prot.c b/arch/powerpc/mm/subpage-prot.c
> index 7c415dd..33fd329 100644
> --- a/arch/powerpc/mm/subpage-prot.c
> +++ b/arch/powerpc/mm/subpage-prot.c
> @@ -130,6 +130,14 @@ static void subpage_prot_clear(unsigned long addr, unsigned long len)
>  	up_write(&mm->mmap_sem);
>  }
>
> +static int subpage_walk_pmd_entry(pmd_t *pmd, unsigned long addr,
> +				  unsigned long end, struct mm_walk *walk)
> +{
> +	struct vm_area_struct *vma = walk->private;
> +	split_huge_page_pmd(vma, addr, pmd);
> +	return 0;
> +}
> +
>  /*
>   * Copy in a subpage protection map for an address range.
>   * The map has 2 bits per 4k subpage, so 32 bits per 64k page.
> @@ -149,6 +157,12 @@ long sys_subpage_prot(unsigned long addr, unsigned long len, u32 __user *map)
>  	size_t nw;
>  	unsigned long next, limit;
>  	int err;
> +	struct vm_area_struct *vma;
> +
> +	struct mm_walk subpage_proto_walk = {
> +		.mm = mm,
> +		.pmd_entry = subpage_walk_pmd_entry,
> +	};
>
>  	/* Check parameters */
>  	if ((addr & ~PAGE_MASK) || (len & ~PAGE_MASK) ||
> @@ -168,6 +182,19 @@ long sys_subpage_prot(unsigned long addr, unsigned long len, u32 __user *map)
>  		return -EFAULT;
>
>  	down_write(&mm->mmap_sem);
> +
> +	/*
> +	 * We don't try too hard, we just mark all the vma in that range
> +	 * VM_NOHUGEPAGE and split them.
> +	 */
> +	for (vma = find_vma(mm, addr);
> +	     (vma && vma->vm_end < (addr + len)); vma = vma->vm_next) {

should be, Missed commit -amend 

	     (vma && vma->vm_start < (addr + len)); vma = vma->vm_next) {

> +		vma->vm_flags |= VM_NOHUGEPAGE;
> +		subpage_proto_walk.private = vma;
> +		walk_page_range(vma->vm_start, vma->vm_end,
> +				&subpage_proto_walk);
> +	}
>  	for (limit = addr + len; addr < limit; addr = next) {
>  		next = pmd_addr_end(addr, limit);
>  		err = -ENOMEM;

-aneesh