Re: [PATCH 1/2] arm64/mm: Directly use TTBRx_EL1_ASID_MASK

[Anshuman Khandual]

On 25/02/26 2:53 PM, Marc Zyngier wrote:
> On Wed, 25 Feb 2026 03:51:56 +0000,
> Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote:
>>
>> Replace all TTBR_ASID_MASK macro instances with TTBRx_EL1_ASID_MASK which
>> is a standard field mask from tools sysreg format. Drop the now redundant
>> custom macro TTBR_ASID_MASK. No functional change.
>>
>> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>> Cc: Will Deacon <will@xxxxxxxxxx>
>> Cc: Marc Zyngier <maz@xxxxxxxxxx>
>> Cc: Oliver Upton <oupton@xxxxxxxxxx>
>> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> Cc: kvmarm@xxxxxxxxxxxxxxx
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
>> ---
>>  arch/arm64/include/asm/asm-uaccess.h | 2 +-
>>  arch/arm64/include/asm/mmu.h         | 1 -
>>  arch/arm64/include/asm/mmu_context.h | 2 +-
>>  arch/arm64/include/asm/uaccess.h     | 6 +++---
>>  arch/arm64/kernel/entry.S            | 2 +-
>>  arch/arm64/kvm/at.c                  | 2 +-
>>  arch/arm64/kvm/nested.c              | 4 ++--
>>  arch/arm64/mm/context.c              | 6 +++---
>>  8 files changed, 12 insertions(+), 13 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
>> index 9148f5a31968..12aa6a283249 100644
>> --- a/arch/arm64/include/asm/asm-uaccess.h
>> +++ b/arch/arm64/include/asm/asm-uaccess.h
>> @@ -15,7 +15,7 @@
>>  #ifdef CONFIG_ARM64_SW_TTBR0_PAN
>>  	.macro	__uaccess_ttbr0_disable, tmp1
>>  	mrs	\tmp1, ttbr1_el1			// swapper_pg_dir
>> -	bic	\tmp1, \tmp1, #TTBR_ASID_MASK
>> +	bic	\tmp1, \tmp1, #TTBRx_EL1_ASID_MASK
>>  	sub	\tmp1, \tmp1, #RESERVED_SWAPPER_OFFSET	// reserved_pg_dir
>>  	msr	ttbr0_el1, \tmp1			// set reserved TTBR0_EL1
>>  	add	\tmp1, \tmp1, #RESERVED_SWAPPER_OFFSET
>> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
>> index 137a173df1ff..019b36cda380 100644
>> --- a/arch/arm64/include/asm/mmu.h
>> +++ b/arch/arm64/include/asm/mmu.h
>> @@ -10,7 +10,6 @@
>>  #define MMCF_AARCH32	0x1	/* mm context flag for AArch32 executables */
>>  #define USER_ASID_BIT	48
>>  #define USER_ASID_FLAG	(UL(1) << USER_ASID_BIT)
>> -#define TTBR_ASID_MASK	(UL(0xffff) << 48)
>>  
>>  #ifndef __ASSEMBLER__
>>  
>> diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
>> index cc80af59c69e..5b1ecde9f14b 100644
>> --- a/arch/arm64/include/asm/mmu_context.h
>> +++ b/arch/arm64/include/asm/mmu_context.h
>> @@ -210,7 +210,7 @@ static inline void update_saved_ttbr0(struct task_struct *tsk,
>>  	if (mm == &init_mm)
>>  		ttbr = phys_to_ttbr(__pa_symbol(reserved_pg_dir));
>>  	else
>> -		ttbr = phys_to_ttbr(virt_to_phys(mm->pgd)) | ASID(mm) << 48;
>> +		ttbr = phys_to_ttbr(virt_to_phys(mm->pgd)) | ASID(mm) << TTBRx_EL1_ASID_SHIFT;
>>
> 
> Could you please use FIELD_PREP() for this sort of constructs?

Will replace with something like the following.

--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -210,7 +210,8 @@ static inline void update_saved_ttbr0(struct task_struct *tsk,
        if (mm == &init_mm)
                ttbr = phys_to_ttbr(__pa_symbol(reserved_pg_dir));
        else
-               ttbr = phys_to_ttbr(virt_to_phys(mm->pgd)) | ASID(mm) << TTBRx_EL1_ASID_SHIFT;
+               ttbr = phys_to_ttbr(virt_to_phys(mm->pgd)) |
+                      FIELD_PREP(TTBRx_EL1_ASID_MASK, ASID(mm));

        WRITE_ONCE(task_thread_info(tsk)->ttbr0, ttbr);
 }

> 
> [...]
> 
>> diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
>> index 885bd5bb2f41..d5c342ccf0f9 100644
>> --- a/arch/arm64/kvm/at.c
>> +++ b/arch/arm64/kvm/at.c
>> @@ -560,7 +560,7 @@ static int walk_s1(struct kvm_vcpu *vcpu, struct s1_walk_info *wi,
>>  			BUG();
>>  		}
>>  
>> -		wr->asid = FIELD_GET(TTBR_ASID_MASK, asid_ttbr);
>> +		wr->asid = FIELD_GET(TTBRx_EL1_ASID_MASK, asid_ttbr);
>>  		if (!kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR0_EL1, ASIDBITS, 16) ||
>>  		    !(tcr & TCR_ASID16))
>>  			wr->asid &= GENMASK(7, 0);
>> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
>> index 620126d1f0dc..82558fb2685f 100644
>> --- a/arch/arm64/kvm/nested.c
>> +++ b/arch/arm64/kvm/nested.c
>> @@ -1343,7 +1343,7 @@ static bool kvm_vncr_tlb_lookup(struct kvm_vcpu *vcpu)
>>  			    vcpu_read_sys_reg(vcpu, TTBR0_EL2));
>>  		u16 asid;
>>  
>> -		asid = FIELD_GET(TTBR_ASID_MASK, ttbr);
>> +		asid = FIELD_GET(TTBRx_EL1_ASID_MASK, ttbr);
>>  		if (!kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR0_EL1, ASIDBITS, 16) ||
>>  		    !(tcr & TCR_ASID16))
>>  			asid &= GENMASK(7, 0);
>> @@ -1459,7 +1459,7 @@ static void kvm_map_l1_vncr(struct kvm_vcpu *vcpu)
>>  			    vcpu_read_sys_reg(vcpu, TTBR0_EL2));
>>  		u16 asid;
>>  
>> -		asid = FIELD_GET(TTBR_ASID_MASK, ttbr);
>> +		asid = FIELD_GET(TTBRx_EL1_ASID_MASK, ttbr);
>>  		if (!kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR0_EL1, ASIDBITS, 16) ||
>>  		    !(tcr & TCR_ASID16))
>>  			asid &= GENMASK(7, 0);
> 
> Given the 3 hunks above, there is clearly a better approach.

Agreed.