Re: [PATCH] powerpc/mm/hugetlb: Filter out hugepage size not supported by page table layout

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

On Monday 20 February 2017 02:35 AM, Benjamin Herrenschmidt wrote:
> On Sun, 2017-02-19 at 15:48 +0530, Aneesh Kumar K.V wrote:
>> +#ifdef CONFIG_PPC_BOOK3S_64
>> +       /*
>> +        * We need to make sure that for different page sizes reported by
>> +        * firmware we only add hugetlb support for page sizes that can be
>> +        * supported by linux page table layout.
>> +        * For now we have
>> +        * Radix: 2M
>> +        * Hash: 16M and 16G
>> +        */
>> +       if (radix_enabled()) {
>> +               if (mmu_psize != MMU_PAGE_2M)
>> +                       return -EINVAL;
>> +       } else {
>> +               if (mmu_psize != MMU_PAGE_16M && mmu_psize != MMU_PAGE_16G)
>> +                       return -EINVAL;
>> +       }
> Hash could support others...

On book3s 64 ? I had the above within #ifdef.

> Same with radix and PUD level pages.

Yes, but gigantic hugepage is not yet supported. Once we add that we will
add MMU_PAGE_1G here.


>
> Why do we need that ? Won't FW provide separate properties for hash and
> radix page sizes anyway ?
>

To avoid crashes like the one reported in the commit message due to 
buggy firmware ? Also
It can serve as an easy way to understand what hugepage sizes are 
supported by different platforms.
I am yet to figure out what the FSL_BOOK3E and PPC_8xx #ifdef above that 
hunk is all about. Having
the supported hugepage size clearly verified against makes it easy ?

-aneesh