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

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Message-ID: <20200201140629.GM22482@gate.crashing.org>
Date:   Sat, 1 Feb 2020 08:06:29 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@....fr>
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

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?


Segher