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Subject: Re: [PATCH 1/2] fs/dax: deposit pagetable even when installing zero
 page
To:     Jan Kara <jack@suse.cz>
Cc:     akpm@linux-foundation.org,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        mpe@ellerman.id.au, Ross Zwisler <zwisler@kernel.org>,
        "Oliver O'Halloran" <oohall@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <20190228083522.8189-1-aneesh.kumar@linux.ibm.com>
 <20190228092101.GA22210@quack2.suse.cz>
From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Date:   Thu, 28 Feb 2019 18:04:24 +0530
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On 2/28/19 2:51 PM, Jan Kara wrote:
> On Thu 28-02-19 14:05:21, Aneesh Kumar K.V wrote:
>> Architectures like ppc64 use the deposited page table to store hardware
>> page table slot information. Make sure we deposit a page table when
>> using zero page at the pmd level for hash.
>>
>> Without this we hit
>>
>> Unable to handle kernel paging request for data at address 0x00000000
>> Faulting instruction address: 0xc000000000082a74
>> Oops: Kernel access of bad area, sig: 11 [#1]
>> ....
>>
>> NIP [c000000000082a74] __hash_page_thp+0x224/0x5b0
>> LR [c0000000000829a4] __hash_page_thp+0x154/0x5b0
>> Call Trace:
>>   hash_page_mm+0x43c/0x740
>>   do_hash_page+0x2c/0x3c
>>   copy_from_iter_flushcache+0xa4/0x4a0
>>   pmem_copy_from_iter+0x2c/0x50 [nd_pmem]
>>   dax_copy_from_iter+0x40/0x70
>>   dax_iomap_actor+0x134/0x360
>>   iomap_apply+0xfc/0x1b0
>>   dax_iomap_rw+0xac/0x130
>>   ext4_file_write_iter+0x254/0x460 [ext4]
>>   __vfs_write+0x120/0x1e0
>>   vfs_write+0xd8/0x220
>>   SyS_write+0x6c/0x110
>>   system_call+0x3c/0x130
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> 
> Thanks for the patch. It looks good to me. You can add:
> 
> Reviewed-by: Jan Kara <jack@suse.cz>
> 
>> ---
>> TODO:
>> * Add fixes tag
> 
> Probably this is a problem since initial PPC PMEM support, isn't it?
> 

Considering ppc64 is the only broken architecture here, I guess I will 
use the commit that enabled PPC PMEM support here.

-aneesh