Re: [PATCH v7 2/8] KVM: arm64: Make vcpu_{read,write}_sys_reg available to HYP code

[Joey Gouly <joey.gouly@arm.com>]

On Wed, Jul 29, 2026 at 02:18:17PM +0100, Fuad Tabba wrote:
> The vcpu_{read,write}_sys_reg() accessors abstract where a system
> register lives, but their VHE implementation cannot be linked into the
> nVHE hypervisor, so exception.c open-codes has_vhe() wrappers instead.
> 
> Redirect the accessors to the raw context accessors for nVHE hyp builds,
> where registers are always in memory, and drop the local wrappers. This
> lets hyp code reuse helpers built on the canonical accessors.
> 
> No functional change intended.
> 
> Suggested-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
> ---
>  arch/arm64/include/asm/kvm_emulate.h |  6 +++++
>  arch/arm64/kvm/hyp/exception.c       | 34 ++++++++--------------------
>  2 files changed, 15 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 5bf3d7e1d92c7..fb4062b3ce55a 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -506,6 +506,12 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
>  	return __vcpu_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK;
>  }
>  
> +/* In nVHE hyp code, registers are always in memory: use the raw accessors. */
> +#if defined(__KVM_NVHE_HYPERVISOR__)
> +#define vcpu_read_sys_reg(v, r)		__vcpu_sys_reg(v, r)
> +#define vcpu_write_sys_reg(v, x, r)	__vcpu_assign_sys_reg(v, r, x)
> +#endif
> +

Does this make sense in arch/arm64/include/asm/kvm_host.h instead? Next
to the definitions of __vcpu_sys_reg() etc.

Thanks,
Joey

>  static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
>  {
>  	if (vcpu_mode_is_32bit(vcpu)) {
> diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
> index bef40ddb16dbc..754e2dc1df54a 100644
> --- a/arch/arm64/kvm/hyp/exception.c
> +++ b/arch/arm64/kvm/hyp/exception.c
> @@ -20,22 +20,6 @@
>  #error Hypervisor code only!
>  #endif
>  
> -static inline u64 __vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
> -{
> -	if (has_vhe())
> -		return vcpu_read_sys_reg(vcpu, reg);
> -
> -	return __vcpu_sys_reg(vcpu, reg);
> -}
> -
> -static inline void __vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
> -{
> -	if (has_vhe())
> -		vcpu_write_sys_reg(vcpu, val, reg);
> -	else
> -		__vcpu_assign_sys_reg(vcpu, reg, val);
> -}
> -
>  static void __vcpu_write_spsr(struct kvm_vcpu *vcpu, unsigned long target_mode,
>  			      u64 val)
>  {
> @@ -101,14 +85,14 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
>  
>  	switch (target_mode) {
>  	case PSR_MODE_EL1h:
> -		vbar = __vcpu_read_sys_reg(vcpu, VBAR_EL1);
> -		sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL1);
> -		__vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL1);
> +		vbar = vcpu_read_sys_reg(vcpu, VBAR_EL1);
> +		sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL1);
> +		vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL1);
>  		break;
>  	case PSR_MODE_EL2h:
> -		vbar = __vcpu_read_sys_reg(vcpu, VBAR_EL2);
> -		sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL2);
> -		__vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL2);
> +		vbar = vcpu_read_sys_reg(vcpu, VBAR_EL2);
> +		sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL2);
> +		vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL2);
>  		break;
>  	default:
>  		/* Don't do that */
> @@ -185,7 +169,7 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
>   */
>  static unsigned long get_except32_cpsr(struct kvm_vcpu *vcpu, u32 mode)
>  {
> -	u32 sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL1);
> +	u32 sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL1);
>  	unsigned long old, new;
>  
>  	old = *vcpu_cpsr(vcpu);
> @@ -281,7 +265,7 @@ static void enter_exception32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)
>  {
>  	unsigned long spsr = *vcpu_cpsr(vcpu);
>  	bool is_thumb = (spsr & PSR_AA32_T_BIT);
> -	u32 sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL1);
> +	u32 sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL1);
>  	u32 return_address;
>  
>  	*vcpu_cpsr(vcpu) = get_except32_cpsr(vcpu, mode);
> @@ -305,7 +289,7 @@ static void enter_exception32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)
>  	if (sctlr & (1 << 13))
>  		vect_offset += 0xffff0000;
>  	else /* always have security exceptions */
> -		vect_offset += __vcpu_read_sys_reg(vcpu, VBAR_EL1);
> +		vect_offset += vcpu_read_sys_reg(vcpu, VBAR_EL1);
>  
>  	*vcpu_pc(vcpu) = vect_offset;
>  }
> -- 
> 2.39.5
>