From: Jean-Philippe Brucker <jean-philippe@linaro.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@linaro.org>
Signed-off-by: Steven Price <steven.price@arm.com>
---
 arch/arm64/include/asm/kvm_rme.h |  1 +
 arch/arm64/kvm/rme.c             | 22 ++++++++++++++++++++++
 arch/arm64/kvm/sys_regs.c        |  2 +-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
index f3ef166e0755..2b454ad633a6 100644
--- a/arch/arm64/include/asm/kvm_rme.h
+++ b/arch/arm64/include/asm/kvm_rme.h
@@ -88,6 +88,7 @@ struct realm_rec {
 
 void kvm_init_rme(void);
 u32 kvm_realm_ipa_limit(void);
+u64 kvm_realm_reset_id_aa64dfr0_el1(struct kvm_vcpu *vcpu, u64 val);
 
 bool kvm_rme_supports_sve(void);
 
diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
index 9a4d0299e56a..87f466e5b548 100644
--- a/arch/arm64/kvm/rme.c
+++ b/arch/arm64/kvm/rme.c
@@ -286,6 +286,28 @@ u32 kvm_realm_ipa_limit(void)
 	return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_S2SZ);
 }
 
+u64 kvm_realm_reset_id_aa64dfr0_el1(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 realm_create_rd(struct kvm *kvm)
 {
 	struct realm *realm = &kvm->arch.realm;
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 10949f3318ed..a73e0eb5dd85 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1746,7 +1746,7 @@ static u64 read_sanitised_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 	/* Hide SPE from guests */
 	val &= ~ID_AA64DFR0_EL1_PMSVer_MASK;
 
-	return val;
+	return kvm_realm_reset_id_aa64dfr0_el1(vcpu, val);
 }
 
 static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
-- 
2.34.1