Subject: Re: [PATCH 1/5] powerpc/64s/hash: Fix 128TB-512TB virtual address boundary case allocation

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 06 Nov 2017 16:08:06 +0530

Nicholas Piggin <[email-masked]> writes:

> When allocating VA space with a hint that crosses 128TB, the SLB addr_limit
> variable is not expanded if addr is not > 128TB, but the slice allocation
> looks at task_size, which is 512TB. This results in slice_check_fit()
> incorrectly succeeding because the slice_count truncates off bit 128 of the
> requested mask, so the comparison to the available mask succeeds.

But then the mask passed to slice_check_fit() is generated using
context.addr_limit as max value. So how did that return succcess? ie,
we get the request mask via

slice_range_to_mask(addr, len, &mask);

And the potential/possible mask using

slice_mask_for_size(mm, psize, &good_mask);

So how did slice_check_fit() return sucess with

slice_check_fit(mm, mask, good_mask);

>
> Fix this by using mm->context.addr_limit instead of mm->task_size for
> testing allocation limits. This causes such allocations to fail.
>
> Cc: "Aneesh Kumar K.V" <[email-masked]>
> Fixes: f4ea6dcb08 ("powerpc/mm: Enable mappings above 128TB")
> Reported-by: Florian Weimer <[email-masked]>
> Signed-off-by: Nicholas Piggin <[email-masked]>
> ---
>  arch/powerpc/mm/slice.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index 45f6740dd407..567db541c0a1 100644
> --- a/arch/powerpc/mm/slice.c
> +++ b/arch/powerpc/mm/slice.c
> @@ -96,7 +96,7 @@ static int slice_area_is_free(struct mm_struct *mm, unsigned long addr,
>  {
>  	struct vm_area_struct *vma;
>
> -	if ((mm->task_size - len) < addr)
> +	if ((mm->context.addr_limit - len) < addr)

I was looking at these as generic boundary check against task size and
for specific range check we should have created mask always using
context.addr_limit. That should keep the boundary condition check same
across radix/hash.

>  		return 0;
>  	vma = find_vma(mm, addr);
>  	return (!vma || (addr + len) <= vm_start_gap(vma));
> @@ -133,7 +133,7 @@ static void slice_mask_for_free(struct mm_struct *mm, struct slice_mask *ret)
>  		if (!slice_low_has_vma(mm, i))
>  			ret->low_slices |= 1u << i;
>
> -	if (mm->task_size <= SLICE_LOW_TOP)
> +	if (mm->context.addr_limit <= SLICE_LOW_TOP)
>  		return;
>
>  	for (i = 0; i < GET_HIGH_SLICE_INDEX(mm->context.addr_limit); i++)
> @@ -446,19 +446,20 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
>
>  	/* Sanity checks */
>  	BUG_ON(mm->task_size == 0);
> +	BUG_ON(mm->context.addr_limit == 0);
>  	VM_BUG_ON(radix_enabled());
>
>  	slice_dbg("slice_get_unmapped_area(mm=%p, psize=%d...\n", mm, psize);
>  	slice_dbg(" addr=%lx, len=%lx, flags=%lx, topdown=%d\n",
>  		  addr, len, flags, topdown);
>
> -	if (len > mm->task_size)
> +	if (len > mm->context.addr_limit)
>  		return -ENOMEM;
>  	if (len & ((1ul << pshift) - 1))
>  		return -EINVAL;
>  	if (fixed && (addr & ((1ul << pshift) - 1)))
>  		return -EINVAL;
> -	if (fixed && addr > (mm->task_size - len))
> +	if (fixed && addr > (mm->context.addr_limit - len))
>  		return -ENOMEM;
>
>  	/* If hint, make sure it matches our alignment restrictions */
> @@ -466,7 +467,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
>  		addr = _ALIGN_UP(addr, 1ul << pshift);
>  		slice_dbg(" aligned addr=%lx\n", addr);
>  		/* Ignore hint if it's too large or overlaps a VMA */
> -		if (addr > mm->task_size - len ||
> +		if (addr > mm->context.addr_limit - len ||
>  		    !slice_area_is_free(mm, addr, len))
>  			addr = 0;
>  	}
> -- 
> 2.15.0