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

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

On 11/06/2017 04:24 PM, Nicholas Piggin wrote:
> On Mon, 06 Nov 2017 16:08:06 +0530
> "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
> 
>> Nicholas Piggin <npiggin@gmail.com> 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);
> 
> Because the addr_limit check is used to *limit* the comparison.
> 
> The available mask had bit up to 127 set, and the mask had 127 and
> 128 set. However the 128T addr_limit causes only bits 0-127 to be
> compared.
>

Should we fix it then via ? I haven't tested this yet. Also this result 
in us comparing more bits?

modified   arch/powerpc/mm/slice.c
@@ -169,13 +169,12 @@ static int slice_check_fit(struct mm_struct *mm,
  			   struct slice_mask mask, struct slice_mask available)
  {
  	DECLARE_BITMAP(result, SLICE_NUM_HIGH);
-	unsigned long slice_count = GET_HIGH_SLICE_INDEX(mm->context.addr_limit);

  	bitmap_and(result, mask.high_slices,
-		   available.high_slices, slice_count);
+		   available.high_slices, SLICE_NUM_HIGH);

  	return (mask.low_slices & available.low_slices) == mask.low_slices &&
-		bitmap_equal(result, mask.high_slices, slice_count);
+		bitmap_equal(result, mask.high_slices, SLICE_NUM_HIGH)


-aneesh