linux-kernel - Re: [PATCH v9 34/43] arm64: RME: Propagate number of breakpoints and watchpoints to userspace

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Message-ID: <20250724102047.GB2753450@e124191.cambridge.arm.com>
Date: Thu, 24 Jul 2025 11:20:47 +0100
From: Joey Gouly <joey.gouly@....com>
To: Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
	Gavin Shan <gshan@...hat.com>,
	Shanker Donthineni <sdonthineni@...dia.com>,
	Alper Gun <alpergun@...gle.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
	Emi Kisanuki <fj0570is@...itsu.com>
Subject: Re: [PATCH v9 34/43] arm64: RME: Propagate number of breakpoints and
 watchpoints to userspace

On Wed, Jun 11, 2025 at 11:48:31AM +0100, Steven Price wrote:
> From: Jean-Philippe Brucker <jean-philippe@...aro.org>
> 
> 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@...aro.org>
> Signed-off-by: Steven Price <steven.price@....com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>

Reviewed-by: Joey Gouly <joey.gouly@....com>

> ---
>  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(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
> index af5150c084ce..c8564d5aaff4 100644
> --- a/arch/arm64/include/asm/kvm_rme.h
> +++ b/arch/arm64/include/asm/kvm_rme.h
> @@ -94,6 +94,8 @@ 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 12cc34192b97..ce8e48ab8753 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;
> +}
> +
>  static int get_start_level(struct realm *realm)
>  {
>  	/*
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index da2d390ce9a5..b974eddfad53 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1847,7 +1847,7 @@ 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,
> -- 
> 2.43.0
>