Re: [PATCH v1 05/11] KVM: arm64: Make vcpu_{read,write}_sys_reg available to HYP code

[Vincent Donnefort <vdonnefort@google.com>]

On Fri, Jun 12, 2026 at 07:59:19AM +0100, tabba@google.com wrote:
> The vcpu_{read,write}_sys_reg() accessors are host-only, so helpers
> built on them such as kvm_vcpu_set_be()/kvm_vcpu_is_be() cannot be
> shared with hyp code. Add _vcpu_read_sys_reg()/_vcpu_write_sys_reg()
> inlines in kvm_emulate.h that dispatch on is_nvhe_hyp_code() to the
> host- or hyp-side accessor. A follow-up series uses this to share that
> emulation code at EL2.
> 
> No functional change intended.
> 
> Signed-off-by: Fuad Tabba <tabba@google.com>
> ---
>  arch/arm64/include/asm/kvm_emulate.h | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 5bf3d7e1d92c..aed9fc0b717b 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -506,6 +506,22 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
>  	return __vcpu_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK;
>  }
>  
> +static inline u64 _vcpu_read_sys_reg(struct kvm_vcpu *vcpu, enum vcpu_sysreg reg)

I am not sure a single underscore is widely used in the kernel.

Why not move __vcpu_read_sys_reg() and __vcpu_write_sys_reg() from exception.c
to kvm_emulate.h? especially this already checks has_vhe().

> +{
> +	if (!is_nvhe_hyp_code())
> +		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, enum vcpu_sysreg reg)
> +{
> +	if (!is_nvhe_hyp_code())
> +		vcpu_write_sys_reg(vcpu, val, reg);
> +	else
> +		__vcpu_assign_sys_reg(vcpu, reg, val);
> +}
> +
>  static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
>  {
>  	if (vcpu_mode_is_32bit(vcpu)) {
> @@ -516,9 +532,9 @@ static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
>  
>  		r = vcpu_has_nv(vcpu) ? SCTLR_EL2 : SCTLR_EL1;
>  
> -		sctlr = vcpu_read_sys_reg(vcpu, r);
> +		sctlr = _vcpu_read_sys_reg(vcpu, r);
>  		sctlr |= SCTLR_ELx_EE;
> -		vcpu_write_sys_reg(vcpu, sctlr, r);
> +		_vcpu_write_sys_reg(vcpu, sctlr, r);
>  	}
>  }
>  
> @@ -533,7 +549,7 @@ static inline bool kvm_vcpu_is_be(struct kvm_vcpu *vcpu)
>  	r = is_hyp_ctxt(vcpu) ? SCTLR_EL2 : SCTLR_EL1;
>  	bit = vcpu_mode_priv(vcpu) ? SCTLR_ELx_EE : SCTLR_EL1_E0E;
>  
> -	return vcpu_read_sys_reg(vcpu, r) & bit;
> +	return _vcpu_read_sys_reg(vcpu, r) & bit;
>  }
>  
>  static inline unsigned long vcpu_data_guest_to_host(struct kvm_vcpu *vcpu,
> -- 
> 2.54.0.1136.gdb2ca164c4-goog
>