Re: [PATCH] MIPS: tlbex: fix a missing statement for HUGETLB

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Hi, David,

For non-Octeon CPU, htlb_info.huge_pte is equal to K0, but I don't
know much about Octeon. So I think you know whether we should use K0
or htlb_info.huge_pte here, since you are the original author.

On Thu, Jul 31, 2014 at 5:44 AM, David Daney <ddaney@xxxxxxxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
>>> Signed-off-by: Binbin Zhou <zhoubb@xxxxxxxxxx>
>>> Cc: <stable@xxxxxxxxxxxxxxx>
>>> ---
>>>   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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