Re: [PATCH v5 2/8] KVM: arm64: Make vcpu_{read,write}_sys_reg available to HYP code

[Vincent Donnefort]

On Tue, Jul 14, 2026 at 11:15:55AM +0100, Fuad Tabba wrote:
> The vcpu_{read,write}_sys_reg() accessors are only valid on a VHE host,
> so helpers built on them such as kvm_vcpu_set_be()/kvm_vcpu_is_be()
> cannot be shared with hyp code. exception.c already wraps them in local
> helpers that pick the host- or hyp-side accessor via has_vhe().
> 
> Rename the host-only implementations to __vcpu_{read,write}_sysreg_vhe()
> and turn vcpu_{read,write}_sys_reg() into the context-dispatching
> wrappers, so every caller gets the version valid in any context and a
> follow-up series can share that emulation code at EL2.
> 
> No functional change intended.
> 
> Signed-off-by: Fuad Tabba <fuad.tabba@xxxxxxxxx>

Reviewed-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>

> ---
> v5:
>   - Named the wrappers vcpu_{read,write}_sys_reg() and renamed the
>     host-only implementations to __vcpu_{read,write}_sysreg_vhe(), rather
>     than introducing a kvm_vcpu_ prefix. (Oliver)
>   - Dropped Vincent's Reviewed-by since the patch changed materially.
> 
>  arch/arm64/include/asm/kvm_emulate.h | 20 ++++++++++++++++
>  arch/arm64/include/asm/kvm_host.h    |  4 ++--
>  arch/arm64/kvm/hyp/exception.c       | 34 ++++++++--------------------
>  arch/arm64/kvm/sys_regs.c            |  4 ++--
>  4 files changed, 33 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 5bf3d7e1d92c7..429bda6f48d94 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -506,6 +506,26 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
>  	return __vcpu_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK;
>  }
>  
> +/*
> + * __vcpu_*_sysreg_vhe() are only valid on a VHE host; wrap them so the same
> + * call site also works at EL2 under nVHE.
> + */
> +static inline u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, enum vcpu_sysreg reg)
> +{
> +	if (has_vhe())
> +		return __vcpu_read_sysreg_vhe(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 (has_vhe())
> +		__vcpu_write_sysreg_vhe(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)) {
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index bae2c4f92ef5c..f3c3c86b3d7fb 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1215,8 +1215,8 @@ u64 kvm_vcpu_apply_reg_masks(const struct kvm_vcpu *, enum vcpu_sysreg, u64);
>  		__v;							\
>  	})
>  
> -u64 vcpu_read_sys_reg(const struct kvm_vcpu *, enum vcpu_sysreg);
> -void vcpu_write_sys_reg(struct kvm_vcpu *, u64, enum vcpu_sysreg);
> +u64 __vcpu_read_sysreg_vhe(const struct kvm_vcpu *vcpu, enum vcpu_sysreg reg);
> +void __vcpu_write_sysreg_vhe(struct kvm_vcpu *vcpu, u64 val, enum vcpu_sysreg reg);
>  
>  struct kvm_vm_stat {
>  	struct kvm_vm_stat_generic generic;
> 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;
>  }
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 08ba882799d48..c6a416974a61f 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -291,7 +291,7 @@ static void write_sr_to_cpu(enum vcpu_sysreg reg, u64 val)
>  	}
>  }
>  
> -u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, enum vcpu_sysreg reg)
> +u64 __vcpu_read_sysreg_vhe(const struct kvm_vcpu *vcpu, enum vcpu_sysreg reg)
>  {
>  	struct sr_loc loc = {};
>  
> @@ -338,7 +338,7 @@ u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, enum vcpu_sysreg reg)
>  	return __vcpu_sys_reg(vcpu, reg);
>  }
>  
> -void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, enum vcpu_sysreg reg)
> +void __vcpu_write_sysreg_vhe(struct kvm_vcpu *vcpu, u64 val, enum vcpu_sysreg reg)
>  {
>  	struct sr_loc loc = {};
>  
> -- 
> 2.39.5
>