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List:       linux-mips
Subject:    Re: [PATCH] MIPS: tlbex: fix a missing statement for HUGETLB
From:       David Daney <ddaney () caviumnetworks ! com>
Date:       2014-07-30 21:44:46
Message-ID: 53D9674E.4000507 () caviumnetworks ! com
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On 07/30/2014 02:41 PM, James Hogan wrote:
> Hi Huacai,
>
> On Tuesday 29 July 2014 14:54:40 Huacai Chen wrote:
>> In commit 2c8c53e28f1 (MIPS: Optimize TLB handlers for Octeon CPUs)
>> build_r4000_tlb_refill_handler() is modified. But it doesn't compatible
>> with the original code in HUGETLB case. Because there is a copy & paste
>> error and one line of code is missing. It is very easy to produce a bug
>> with LTP's hugemmap05 test.
>>
>> Signed-off-by: Huacai Chen <chenhc@lemote.com>
>> Signed-off-by: Binbin Zhou <zhoubb@lemote.com>
>> Cc: <stable@vger.kernel.org>
>> ---
>>   arch/mips/mm/tlbex.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
>> index e80e10b..343fe0f 100644
>> --- a/arch/mips/mm/tlbex.c
>> +++ b/arch/mips/mm/tlbex.c
>> @@ -1299,6 +1299,7 @@ static void build_r4000_tlb_refill_handler(void)
>>   	}
>>   #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
>>   	uasm_l_tlb_huge_update(&l, p);
>> +	UASM_i_LW(&p, K0, 0, K1);
>>   	build_huge_update_entries(&p, htlb_info.huge_pte, K1);
>>   	build_huge_tlb_write_entry(&p, &l, &r, K0, tlb_random,
>>   				   htlb_info.restore_scratch);
>
> build_huge_tlb_write_entry only uses K0 as a temp and clobbers without using
> the value, so the K0 must be being used by the code generated by
> build_huge_update_entires, but the patch you mentioned changed the second
> argument from K0 to htlb_info.huge_pte.
>
> So should the K0 in the new UASM_i_LW call be changed to htlb_info.huge_pte
> too?
>

I don't know.  You have to dump out the generated handler (by #define 
DEBUG at the top of the file), then assemble/disassemble it.  Looking at 
the disassembly, we could make sensible statements about what is happening.


> (David Daney on Cc)
>
> Thanks
> James
>


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