Re: [PATCH v13 45/48] arm64: RMI: Provide accurate register list

[Wei-Lin Chang]

On Wed, Mar 18, 2026 at 03:54:09PM +0000, Steven Price wrote:
> From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> 
> Userspace can set a few registers with KVM_SET_ONE_REG (9 GP registers
> at runtime, and 3 system registers during initialization). Update the
> register list returned by KVM_GET_REG_LIST.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
> Changes since v11:
>  * Reworked due to upstream changes.
> Changes since v8:
>  * Minor type changes following review.
> Changes since v7:
>  * Reworked on upstream changes.
> ---
>  arch/arm64/kvm/guest.c      |  6 ++++++
>  arch/arm64/kvm/hypercalls.c |  4 ++--
>  arch/arm64/kvm/sys_regs.c   | 29 +++++++++++++++++++++++------
>  3 files changed, 31 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 2c4db2d1a6ca..23fdb2ee8a61 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -620,6 +620,9 @@ static unsigned long num_sve_regs(const struct kvm_vcpu *vcpu)
>  	if (!kvm_arm_vcpu_sve_finalized(vcpu))
>  		return 1; /* KVM_REG_ARM64_SVE_VLS */
>  
> +	if (kvm_is_realm(vcpu->kvm))
> +		return 1; /* KVM_REG_ARM64_SVE_VLS */
> +
>  	return slices * (SVE_NUM_PREGS + SVE_NUM_ZREGS + 1 /* FFR */)
>  		+ 1; /* KVM_REG_ARM64_SVE_VLS */
>  }
> @@ -647,6 +650,9 @@ static int copy_sve_reg_indices(const struct kvm_vcpu *vcpu,
>  	if (!kvm_arm_vcpu_sve_finalized(vcpu))
>  		return num_regs;
>  
> +	if (kvm_is_realm(vcpu->kvm))
> +		return num_regs;
> +
>  	for (i = 0; i < slices; i++) {
>  		for (n = 0; n < SVE_NUM_ZREGS; n++) {
>  			reg = KVM_REG_ARM64_SVE_ZREG(n, i);
> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> index 58c5fe7d7572..70ac7971416c 100644
> --- a/arch/arm64/kvm/hypercalls.c
> +++ b/arch/arm64/kvm/hypercalls.c
> @@ -414,14 +414,14 @@ void kvm_arm_teardown_hypercalls(struct kvm *kvm)
>  
>  int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
>  {
> -	return ARRAY_SIZE(kvm_arm_fw_reg_ids);
> +	return kvm_is_realm(vcpu->kvm) ? 0 : ARRAY_SIZE(kvm_arm_fw_reg_ids);
>  }
>  
>  int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
>  {
>  	int i;
>  
> -	for (i = 0; i < ARRAY_SIZE(kvm_arm_fw_reg_ids); i++) {
> +	for (i = 0; i < kvm_arm_get_fw_num_regs(vcpu); i++) {
>  		if (put_user(kvm_arm_fw_reg_ids[i], uindices++))
>  			return -EFAULT;
>  	}
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index ebb428b861f5..088d900b9c3a 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -5436,18 +5436,18 @@ int kvm_arm_sys_reg_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
>  				    sys_reg_descs, ARRAY_SIZE(sys_reg_descs));
>  }
>  
> -static unsigned int num_demux_regs(void)
> +static inline unsigned int num_demux_regs(struct kvm_vcpu *vcpu)
>  {
> -	return CSSELR_MAX;
> +	return kvm_is_realm(vcpu->kvm) ? 0 : CSSELR_MAX;
>  }
>  
> -static int write_demux_regids(u64 __user *uindices)
> +static int write_demux_regids(struct kvm_vcpu *vcpu, u64 __user *uindices)
>  {
>  	u64 val = KVM_REG_ARM64 | KVM_REG_SIZE_U32 | KVM_REG_ARM_DEMUX;
>  	unsigned int i;
>  
>  	val |= KVM_REG_ARM_DEMUX_ID_CCSIDR;
> -	for (i = 0; i < CSSELR_MAX; i++) {
> +	for (i = 0; i < num_demux_regs(vcpu); i++) {
>  		if (put_user(val | i, uindices))
>  			return -EFAULT;
>  		uindices++;
> @@ -5491,11 +5491,28 @@ static bool copy_reg_to_user(const struct sys_reg_desc *reg, u64 __user **uind)
>  	return true;
>  }
>  
> +static inline bool kvm_realm_sys_reg_hidden_user(const struct kvm_vcpu *vcpu,
> +						 u64 reg)
> +{
> +	if (!kvm_is_realm(vcpu->kvm))
> +		return false;
> +
> +	switch (reg) {
> +	case SYS_ID_AA64DFR0_EL1:
> +	case SYS_PMCR_EL0:
> +		return false;
> +	}
> +	return true;
> +}
> +
>  static int walk_one_sys_reg(const struct kvm_vcpu *vcpu,
>  			    const struct sys_reg_desc *rd,
>  			    u64 __user **uind,
>  			    unsigned int *total)
>  {
> +	if (kvm_realm_sys_reg_hidden_user(vcpu, reg_to_encoding(rd)))

Hi,

Same as my comment for patch 39, I would suggest moving the
kvm_is_realm() check out of this function.

Thanks,
Wei-Lin Chang

> +		return 0;
> +
>  	/*
>  	 * Ignore registers we trap but don't save,
>  	 * and for which no custom user accessor is provided.
> @@ -5533,7 +5550,7 @@ static int walk_sys_regs(struct kvm_vcpu *vcpu, u64 __user *uind)
>  
>  unsigned long kvm_arm_num_sys_reg_descs(struct kvm_vcpu *vcpu)
>  {
> -	return num_demux_regs()
> +	return num_demux_regs(vcpu)
>  		+ walk_sys_regs(vcpu, (u64 __user *)NULL);
>  }
>  
> @@ -5546,7 +5563,7 @@ int kvm_arm_copy_sys_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
>  		return err;
>  	uindices += err;
>  
> -	return write_demux_regids(uindices);
> +	return write_demux_regids(vcpu, uindices);
>  }
>  
>  #define KVM_ARM_FEATURE_ID_RANGE_INDEX(r)			\
> -- 
> 2.43.0
>