linux-kernel - [PATCH v12 42/46] arm64: RMI: Configure max SVE vector length for a Realm

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Message-ID: <20251217101125.91098-43-steven.price@arm.com>
Date: Wed, 17 Dec 2025 10:11:19 +0000
From: Steven Price <steven.price@....com>
To: kvm@...r.kernel.org,
	kvmarm@...ts.linux.dev
Cc: 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,
	Joey Gouly <joey.gouly@....com>,
	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>,
	Vishal Annapurve <vannapurve@...gle.com>,
	Steven Price <steven.price@....com>
Subject: [PATCH v12 42/46] arm64: RMI: Configure max SVE vector length for a Realm

From: Jean-Philippe Brucker <jean-philippe@...aro.org>

Obtain the max vector length configured by userspace on the vCPUs, and
write it into the Realm parameters. By default the vCPU is configured
with the max vector length reported by RMM, and userspace can reduce it
with a write to KVM_REG_ARM64_SVE_VLS.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
Signed-off-by: Steven Price <steven.price@....com>
---
Changes since v6:
 * Rename max_vl/realm_max_vl to vl/last_vl - there is nothing "maximum"
   about them, we're just checking that all realms have the same vector
   length
---
 arch/arm64/kvm/guest.c |  3 ++-
 arch/arm64/kvm/rmi.c   | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 705c2ccc335d..999edf0b5219 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -361,7 +361,7 @@ static int set_sve_vls(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 	if (!vcpu_has_sve(vcpu))
 		return -ENOENT;
 
-	if (kvm_arm_vcpu_sve_finalized(vcpu))
+	if (kvm_arm_vcpu_sve_finalized(vcpu) || kvm_realm_is_created(vcpu->kvm))
 		return -EPERM; /* too late! */
 
 	if (WARN_ON(vcpu->arch.sve_state))
@@ -756,6 +756,7 @@ static bool validate_realm_set_reg(struct kvm_vcpu *vcpu,
 		switch (reg->id) {
 		case KVM_REG_ARM_PMCR_EL0:
 		case KVM_REG_ARM_ID_AA64DFR0_EL1:
+		case KVM_REG_ARM64_SVE_VLS:
 			return true;
 		}
 	}
diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
index b719c39329c8..657d70eab0ab 100644
--- a/arch/arm64/kvm/rmi.c
+++ b/arch/arm64/kvm/rmi.c
@@ -557,6 +557,39 @@ static void realm_unmap_shared_range(struct kvm *kvm,
 			     start, end);
 }
 
+static int realm_init_sve_param(struct kvm *kvm, struct realm_params *params)
+{
+	unsigned long i;
+	struct kvm_vcpu *vcpu;
+	int vl, last_vl = -1;
+
+	if (!kvm_has_sve(kvm))
+		return 0;
+
+	/*
+	 * Get the preferred SVE configuration, set by userspace with the
+	 * KVM_ARM_VCPU_SVE feature and KVM_REG_ARM64_SVE_VLS pseudo-register.
+	 */
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		if (!kvm_arm_vcpu_sve_finalized(vcpu))
+			return -EINVAL;
+
+		vl = vcpu->arch.sve_max_vl;
+
+		/* We need all vCPUs to have the same SVE config */
+		if (last_vl >= 0 && last_vl != vl)
+			return -EINVAL;
+
+		last_vl = vl;
+	}
+
+	if (last_vl > 0) {
+		params->sve_vl = sve_vq_from_vl(last_vl) - 1;
+		params->flags |= RMI_REALM_PARAM_FLAG_SVE;
+	}
+	return 0;
+}
+
 /* Calculate the number of s2 root rtts needed */
 static int realm_num_root_rtts(struct realm *realm)
 {
@@ -623,6 +656,10 @@ static int realm_create_rd(struct kvm *kvm)
 		params->flags |= RMI_REALM_PARAM_FLAG_PMU;
 	}
 
+	r = realm_init_sve_param(kvm, params);
+	if (r)
+		goto out_undelegate_tables;
+
 	params_phys = virt_to_phys(params);
 
 	if (rmi_realm_create(rd_phys, params_phys)) {
-- 
2.43.0