Re: [PATCH v7 35/45] arm64: RME: Propagate number of breakpoints and watchpoints to userspace

[Gavin Shan <gshan@xxxxxxxxxx>]

On 2/14/25 2:14 AM, Steven Price wrote:
> From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
>
> The RMM describes the maximum number of BPs/WPs available to the guest
> in the Feature Register 0. Propagate those numbers into ID_AA64DFR0_EL1,
> which is visible to userspace. A VMM needs this information in order to
> set up realm parameters.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
>   arch/arm64/include/asm/kvm_rme.h |  2 ++
>   arch/arm64/kvm/rme.c             | 22 ++++++++++++++++++++++
>   arch/arm64/kvm/sys_regs.c        |  2 +-
>   3 files changed, 25 insertions(+), 1 deletion(-)

With the following one nitpick addressed:

Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>

> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
> index d684b30493f5..67ee38541a82 100644
> --- a/arch/arm64/include/asm/kvm_rme.h
> +++ b/arch/arm64/include/asm/kvm_rme.h
> @@ -85,6 +85,8 @@ void kvm_init_rme(void);
>   u32 kvm_realm_ipa_limit(void);
>   u32 kvm_realm_vgic_nr_lr(void);
>   
> +u64 kvm_realm_reset_id_aa64dfr0_el1(const struct kvm_vcpu *vcpu, u64 val);
> +
>   bool kvm_rme_supports_sve(void);
>   
>   int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
> index f83f34358832..8c426f575728 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -87,6 +87,28 @@ u32 kvm_realm_vgic_nr_lr(void)
>   	return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_GICV3_NUM_LRS);
>   }
>   
> +u64 kvm_realm_reset_id_aa64dfr0_el1(const struct kvm_vcpu *vcpu, u64 val)
> +{
> +	u32 bps = u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_NUM_BPS);
> +	u32 wps = u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_NUM_WPS);
> +	u32 ctx_cmps;
> +
> +	if (!kvm_is_realm(vcpu->kvm))
> +		return val;
> +
> +	/* Ensure CTX_CMPs is still valid */
> +	ctx_cmps = FIELD_GET(ID_AA64DFR0_EL1_CTX_CMPs, val);
> +	ctx_cmps = min(bps, ctx_cmps);
> +
> +	val &= ~(ID_AA64DFR0_EL1_BRPs_MASK | ID_AA64DFR0_EL1_WRPs_MASK |
> +		 ID_AA64DFR0_EL1_CTX_CMPs);
> +	val |= FIELD_PREP(ID_AA64DFR0_EL1_BRPs_MASK, bps) |
> +	       FIELD_PREP(ID_AA64DFR0_EL1_WRPs_MASK, wps) |
> +	       FIELD_PREP(ID_AA64DFR0_EL1_CTX_CMPs, ctx_cmps);
> +
> +	return val;
> +}
> +

The chunk of code can be squeezed to sys_reg.c::sanitise_id_aa64dfr0_el1() since
sys_reg.c has been plumbed for realm, no reason to keep a separate helper in rme.c
because it's only called by sys_reg.c::sanitise_id_aa64dfr0_el1()

>   static int get_start_level(struct realm *realm)
>   {
>   	return 4 - ((realm->ia_bits - 8) / (RMM_PAGE_SHIFT - 3));
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index ed881725eb64..5618eff33155 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1820,7 +1820,7 @@ static u64 sanitise_id_aa64dfr0_el1(const struct kvm_vcpu *vcpu, u64 val)
>   	/* Hide BRBE from guests */
>   	val &= ~ID_AA64DFR0_EL1_BRBE_MASK;
>   
> -	return val;
> +	return kvm_realm_reset_id_aa64dfr0_el1(vcpu, val);
>   }
>   
>   static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,

Thanks,
Gavin