[PATCH] arm64: Fix double TCR_T0SZ_OFFSET shift

[PATCH] arm64: Fix double TCR_T0SZ_OFFSET shift

[Seongsu Park]

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@gamil.com>
Signed-off-by: Leem ChaeHoon <infinite.run@gamil.com>
Co-developed-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
Signed-off-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
Co-developed-by: Soomin Cho <to.soomin@gmail.com>
Signed-off-by: Soomin Cho <to.soomin@gmail.com>
Co-developed-by: DaeRo Lee <skseofh@gmail.com>
Signed-off-by: DaeRo Lee <skseofh@gmail.com>
Co-developed-by: kmasta <kmasta.study@gmail.com>
Signed-off-by: kmasta <kmasta.study@gmail.com>
Signed-off-by: Seongsu Park <sgsu.park@samsung.com>
---
 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;
 	write_sysreg(tcr, tcr_el1);
 	isb();
 }
-- 
2.34.1

[PATCH] arm64: Fix double TCR_T0SZ_OFFSET shift

[Seongsu Park]

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@gmail.com>
Signed-off-by: Leem ChaeHoon <infinite.run@gmail.com>
Co-developed-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
Signed-off-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
Co-developed-by: Soomin Cho <to.soomin@gmail.com>
Signed-off-by: Soomin Cho <to.soomin@gmail.com>
Co-developed-by: DaeRo Lee <skseofh@gmail.com>
Signed-off-by: DaeRo Lee <skseofh@gmail.com>
Co-developed-by: kmasta <kmasta.study@gmail.com>
Signed-off-by: kmasta <kmasta.study@gmail.com>
Signed-off-by: Seongsu Park <sgsu.park@samsung.com>
---
 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;
 	write_sysreg(tcr, tcr_el1);
 	isb();
 }
-- 
2.34.1

Re: [PATCH] arm64: Fix double TCR_T0SZ_OFFSET shift

[Will Deacon]

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@gmail.com>
> Signed-off-by: Leem ChaeHoon <infinite.run@gmail.com>
> Co-developed-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
> Signed-off-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
> Co-developed-by: Soomin Cho <to.soomin@gmail.com>
> Signed-off-by: Soomin Cho <to.soomin@gmail.com>
> Co-developed-by: DaeRo Lee <skseofh@gmail.com>
> Signed-off-by: DaeRo Lee <skseofh@gmail.com>
> Co-developed-by: kmasta <kmasta.study@gmail.com>
> Signed-off-by: kmasta <kmasta.study@gmail.com>
> Signed-off-by: Seongsu Park <sgsu.park@samsung.com>

heh, that's quite a lot of people. Did you remove three chars each? :p

> ---
>  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

RE: [PATCH] arm64: Fix double TCR_T0SZ_OFFSET shift

[Seongsu Park]

> 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@gmail.com>
> > Signed-off-by: Leem ChaeHoon <infinite.run@gmail.com>
> > Co-developed-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
> > Signed-off-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
> > Co-developed-by: Soomin Cho <to.soomin@gmail.com>
> > Signed-off-by: Soomin Cho <to.soomin@gmail.com>
> > Co-developed-by: DaeRo Lee <skseofh@gmail.com>
> > Signed-off-by: DaeRo Lee <skseofh@gmail.com>
> > Co-developed-by: kmasta <kmasta.study@gmail.com>
> > Signed-off-by: kmasta <kmasta.study@gmail.com>
> > Signed-off-by: Seongsu Park <sgsu.park@samsung.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.

Re: [PATCH] arm64: Fix double TCR_T0SZ_OFFSET shift

[Robin Murphy]

On 2024-04-02 11:47 am, 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.

If the shift for assigning the t0sz value to the TCR field is wrong, 
then the other shift for comparing the same t0sz value to the existing 
TCR field must also be wrong. Really, this many people involved in 
writing a patch and still nobody spotted the obvious?

Thanks,
Robin.

> Co-developed-by: Leem ChaeHoon <infinite.run@gamil.com>
> Signed-off-by: Leem ChaeHoon <infinite.run@gamil.com>
> Co-developed-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
> Signed-off-by: Gyeonggeon Choi <gychoi@student.42seoul.kr>
> Co-developed-by: Soomin Cho <to.soomin@gmail.com>
> Signed-off-by: Soomin Cho <to.soomin@gmail.com>
> Co-developed-by: DaeRo Lee <skseofh@gmail.com>
> Signed-off-by: DaeRo Lee <skseofh@gmail.com>
> Co-developed-by: kmasta <kmasta.study@gmail.com>
> Signed-off-by: kmasta <kmasta.study@gmail.com>
> Signed-off-by: Seongsu Park <sgsu.park@samsung.com>
> ---
>   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;
>   	write_sysreg(tcr, tcr_el1);
>   	isb();
>   }