linux-kernel - RE: [PATCH] arm64: Fix double TCR_T0SZ

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Date: Wed, 3 Apr 2024 11:08:31 +0900
From: "Seongsu Park" <sgsu.park@...sung.com>
To: "'Will Deacon'" <will@...nel.org>
Cc: <catalin.marinas@....com>, <ardb@...nel.org>, <mark.rutland@....com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	"'Leem	ChaeHoon'" <infinite.run@...il.com>, "'Gyeonggeon Choi'"
	<gychoi@...dent.42seoul.kr>, "'Soomin Cho'" <to.soomin@...il.com>, "'DaeRo
 Lee'" <skseofh@...il.com>, "'kmasta'" <kmasta.study@...il.com>
Subject: RE: [PATCH] arm64: Fix double TCR_T0SZ_OFFSET shift



> On Tue, Apr 02, 2024 at 07:49:50PM +0900, Seongsu Park wrote:
> > We have already shifted the value of t0sz in TCR_T0SZ by
TCR_T0SZ_OFFSET.
> > So, the TCR_T0SZ_OFFSET shift here should be removed.
> >
> > Co-developed-by: Leem ChaeHoon <infinite.run@...il.com>
> > Signed-off-by: Leem ChaeHoon <infinite.run@...il.com>
> > Co-developed-by: Gyeonggeon Choi <gychoi@...dent.42seoul.kr>
> > Signed-off-by: Gyeonggeon Choi <gychoi@...dent.42seoul.kr>
> > Co-developed-by: Soomin Cho <to.soomin@...il.com>
> > Signed-off-by: Soomin Cho <to.soomin@...il.com>
> > Co-developed-by: DaeRo Lee <skseofh@...il.com>
> > Signed-off-by: DaeRo Lee <skseofh@...il.com>
> > Co-developed-by: kmasta <kmasta.study@...il.com>
> > Signed-off-by: kmasta <kmasta.study@...il.com>
> > Signed-off-by: Seongsu Park <sgsu.park@...sung.com>
> 
> heh, that's quite a lot of people. Did you remove three chars each? :p
We are studying the Linux kernel based on arm64 together every Saturday for
7 hours! :)
> 
> > ---
> >  arch/arm64/include/asm/mmu_context.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/include/asm/mmu_context.h
> > b/arch/arm64/include/asm/mmu_context.h
> > index c768d16b81a4..58de99836d2e 100644
> > --- a/arch/arm64/include/asm/mmu_context.h
> > +++ b/arch/arm64/include/asm/mmu_context.h
> > @@ -76,7 +76,7 @@ static inline void __cpu_set_tcr_t0sz(unsigned long
> t0sz)
> >  		return;
> >
> >  	tcr &= ~TCR_T0SZ_MASK;
> > -	tcr |= t0sz << TCR_T0SZ_OFFSET;
> > +	tcr |= t0sz;
> 
> Thankfully, TCR_T0SZ_OFFSET is 0 so this isn't as alarming as it looks.
> Even so, if we're going to make the code consistent, then shouldn't the
> earlier conditional be updated too?
> 
> 	if ((tcr & TCR_T0SZ_MASK) >> TCR_T0SZ_OFFSET == t0sz)
> 		return;
> 
> seems to assume that t0sz is unshifted.
> 
> Will
Thank you for feedback. I'll send v2 patch.