[PATCH] arm64: Cleanup __cpu_set_tcr_t0sz()

[PATCH] arm64: Cleanup __cpu_set_tcr_t0sz()

[Seongsu Park]

The T0SZ field of TCR_EL1 occupies bits 0-5 of the register and encode
the virtual address space translated by TTBR0_EL1. When updating the
field, for example because we are switching to/from the idmap page-table,
__cpu_set_tcr_t0sz() erroneously treats its 't0sz' argument as unshifted,
resulting in harmless but confusing double shifts by 0 in the code.

Co-developed-by: Leem ChaeHoon <infinite.run@gmail.com>
Signed-off-by: Leem ChaeHoon <infinite.run@gmail.com>
Signed-off-by: Seongsu Park <sgsu.park@samsung.com>
---
 arch/arm64/include/asm/mmu_context.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index c768d16b81a4..bd19f4c758b7 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -72,11 +72,11 @@ static inline void __cpu_set_tcr_t0sz(unsigned long t0sz)
 {
 	unsigned long tcr = read_sysreg(tcr_el1);
 
-	if ((tcr & TCR_T0SZ_MASK) >> TCR_T0SZ_OFFSET == t0sz)
+	if ((tcr & TCR_T0SZ_MASK) == 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: Cleanup __cpu_set_tcr_t0sz()

[Seongsu Park]

Dear All,

Please check this patch.
I think this patch is appropriate.

Thanks.
Seongsu Park.

> -----Original Message-----
> From: Seongsu Park <sgsu.park@samsung.com>
> Sent: Thursday, May 23, 2024 9:22 PM
> To: catalin.marinas@arm.com; will@kernel.org; ardb@kernel.org;
> mark.rutland@arm.com
> Cc: linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> infinite.run@gmail.com; sgsu.park@samsung.com
> Subject: [PATCH] arm64: Cleanup __cpu_set_tcr_t0sz()
> 
> The T0SZ field of TCR_EL1 occupies bits 0-5 of the register and encode the
> virtual address space translated by TTBR0_EL1. When updating the field,
> for example because we are switching to/from the idmap page-table,
> __cpu_set_tcr_t0sz() erroneously treats its 't0sz' argument as unshifted,
> resulting in harmless but confusing double shifts by 0 in the code.
> 
> Co-developed-by: Leem ChaeHoon <infinite.run@gmail.com>
> Signed-off-by: Leem ChaeHoon <infinite.run@gmail.com>
> Signed-off-by: Seongsu Park <sgsu.park@samsung.com>
> ---
>  arch/arm64/include/asm/mmu_context.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/mmu_context.h
> b/arch/arm64/include/asm/mmu_context.h
> index c768d16b81a4..bd19f4c758b7 100644
> --- a/arch/arm64/include/asm/mmu_context.h
> +++ b/arch/arm64/include/asm/mmu_context.h
> @@ -72,11 +72,11 @@ static inline void __cpu_set_tcr_t0sz(unsigned long
> t0sz)  {
>  	unsigned long tcr = read_sysreg(tcr_el1);
> 
> -	if ((tcr & TCR_T0SZ_MASK) >> TCR_T0SZ_OFFSET == t0sz)
> +	if ((tcr & TCR_T0SZ_MASK) == 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: Cleanup __cpu_set_tcr_t0sz()

[Seongsu Park]

Dear Will,

Could you check this patch?
This patch will make the code more stable.

Thanks.
Seongsu Park.

> -----Original Message-----
> From: Seongsu Park <sgsu.park@samsung.com>
> Sent: Monday, June 3, 2024 8:03 PM
> To: 'catalin.marinas@arm.com' <catalin.marinas@arm.com>; 'will@kernel.org'
> <will@kernel.org>; 'ardb@kernel.org' <ardb@kernel.org>;
> 'mark.rutland@arm.com' <mark.rutland@arm.com>
> Cc: 'linux-arm-kernel@lists.infradead.org' <linux-arm-
> kernel@lists.infradead.org>; 'linux-kernel@vger.kernel.org' <linux-
> kernel@vger.kernel.org>; 'infinite.run@gmail.com' <infinite.run@gmail.com>;
> 'sgsu.park@samsung.com' <sgsu.park@samsung.com>
> Subject: RE: [PATCH] arm64: Cleanup __cpu_set_tcr_t0sz()
> 
> Dear All,
> 
> Please check this patch.
> I think this patch is appropriate.
> 
> Thanks.
> Seongsu Park.
> 
> > -----Original Message-----
> > From: Seongsu Park <sgsu.park@samsung.com>
> > Sent: Thursday, May 23, 2024 9:22 PM
> > To: catalin.marinas@arm.com; will@kernel.org; ardb@kernel.org;
> > mark.rutland@arm.com
> > Cc: linux-arm-kernel@lists.infradead.org;
> > linux-kernel@vger.kernel.org; infinite.run@gmail.com;
> > sgsu.park@samsung.com
> > Subject: [PATCH] arm64: Cleanup __cpu_set_tcr_t0sz()
> >
> > The T0SZ field of TCR_EL1 occupies bits 0-5 of the register and encode
> > the virtual address space translated by TTBR0_EL1. When updating the
> > field, for example because we are switching to/from the idmap
> > page-table,
> > __cpu_set_tcr_t0sz() erroneously treats its 't0sz' argument as
> > unshifted, resulting in harmless but confusing double shifts by 0 in the
> code.
> >
> > Co-developed-by: Leem ChaeHoon <infinite.run@gmail.com>
> > Signed-off-by: Leem ChaeHoon <infinite.run@gmail.com>
> > Signed-off-by: Seongsu Park <sgsu.park@samsung.com>
> > ---
> >  arch/arm64/include/asm/mmu_context.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/mmu_context.h
> > b/arch/arm64/include/asm/mmu_context.h
> > index c768d16b81a4..bd19f4c758b7 100644
> > --- a/arch/arm64/include/asm/mmu_context.h
> > +++ b/arch/arm64/include/asm/mmu_context.h
> > @@ -72,11 +72,11 @@ static inline void __cpu_set_tcr_t0sz(unsigned
> > long
> > t0sz)  {
> >  	unsigned long tcr = read_sysreg(tcr_el1);
> >
> > -	if ((tcr & TCR_T0SZ_MASK) >> TCR_T0SZ_OFFSET == t0sz)
> > +	if ((tcr & TCR_T0SZ_MASK) == 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: Cleanup __cpu_set_tcr_t0sz()

[Catalin Marinas]

On Thu, 23 May 2024 21:21:46 +0900, Seongsu Park wrote:
> The T0SZ field of TCR_EL1 occupies bits 0-5 of the register and encode
> the virtual address space translated by TTBR0_EL1. When updating the
> field, for example because we are switching to/from the idmap page-table,
> __cpu_set_tcr_t0sz() erroneously treats its 't0sz' argument as unshifted,
> resulting in harmless but confusing double shifts by 0 in the code.
> 
> 
> [...]

Applied to arm64 (for-next/misc), thanks!

[1/1] arm64: Cleanup __cpu_set_tcr_t0sz()
      https://git.kernel.org/arm64/c/cf938f91784f

-- 
Catalin