linux-kernel - Re: [PATCH] powerpc/32s: Don't flush all TLBs when flushing one page

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Date:   Sat, 1 Feb 2020 15:53:12 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/32s: Don't flush all TLBs when flushing one page



Le 01/02/2020 à 15:06, Segher Boessenkool a écrit :
> On Sat, Feb 01, 2020 at 08:27:03AM +0100, Christophe Leroy wrote:
>> Le 31/01/2020 à 20:38, Segher Boessenkool a écrit :
>>> On Fri, Jan 31, 2020 at 05:15:20PM +0100, Christophe Leroy wrote:
>>>> Le 31/01/2020 à 16:51, Segher Boessenkool a écrit :
>>>>> On Fri, Jan 31, 2020 at 03:37:34PM +0000, Christophe Leroy wrote:
>>>>>> When the range is a single page, do a page flush instead.
>>>>>
>>>>>> +	start &= PAGE_MASK;
>>>>>> +	end = (end - 1) | ~PAGE_MASK;
>>>>>>   	if (!Hash) {
>>>>>> -		_tlbia();
>>>>>> +		if (end - start == PAGE_SIZE)
>>>>>> +			_tlbie(start);
>>>>>> +		else
>>>>>> +			_tlbia();
>>>>>>   		return;
>>>>>>   	}
>>>>>
>>>>> For just one page, you get  end - start == 0  actually?
>>>>
>>>> Oops, good catch.
>>>>
>>>> Indeed you don't get PAGE_SIZE but (PAGE_SIZE - 1) for just one page.
>>>
>>> You have all low bits masked off in both start and end, so you get zero.
>>> You could make the condion read "if (start == end)?
>>
>> No, in end the low bits are set, that's a BIT OR with ~PAGE_MASK, so it
>> sets all low bits to 1.
> 
> Oh, wow, yes, I cannot read apparently.
> 
> Maybe there are some ROUND_DOWN and ROUND_UP macros you could use?
> 

Yes but my intention was to modify the existing code as less as possible.
What do you think about version v2 of the patch ?

Christophe