linux-kernel - [PATCH v12 23/46] arm64: RMI: Add a VMID allocator for realms

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Message-ID: <20251217101125.91098-24-steven.price@arm.com>
Date: Wed, 17 Dec 2025 10:11:00 +0000
From: Steven Price <steven.price@....com>
To: kvm@...r.kernel.org,
	kvmarm@...ts.linux.dev
Cc: Steven Price <steven.price@....com>,
	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>
Subject: [PATCH v12 23/46] arm64: RMI: Add a VMID allocator for realms

The RMM v1.0 spec requires that the host manage the VMIDs of realm
guests. Add a basic allocator and assign a unique VMID to the guest when
creating the realm descriptor.

Signed-off-by: Steven Price <steven.price@....com>
---
New patch for v12.
NOTE: RMM v2.0 will remove the requirement for the host to manage VMIDs
---
 arch/arm64/kvm/rmi.c | 48 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
index 18edc7eeb5fa..ede6c250bcfb 100644
--- a/arch/arm64/kvm/rmi.c
+++ b/arch/arm64/kvm/rmi.c
@@ -600,6 +600,42 @@ static int realm_create_rd(struct kvm *kvm)
 	return r;
 }
 
+/* Protects access to rmi_vmid_bitmap */
+static DEFINE_SPINLOCK(rmi_vmid_lock);
+static unsigned long *rmi_vmid_bitmap;
+
+static int rmi_vmid_init(void)
+{
+	unsigned int vmid_count = 1 << kvm_get_vmid_bits();
+
+	rmi_vmid_bitmap = bitmap_zalloc(vmid_count, GFP_KERNEL);
+	if (!rmi_vmid_bitmap) {
+		kvm_err("%s: Couldn't allocate rmi vmid bitmap\n", __func__);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static int rmi_vmid_reserve(void)
+{
+	int ret;
+	unsigned int vmid_count = 1 << kvm_get_vmid_bits();
+
+	spin_lock(&rmi_vmid_lock);
+	ret = bitmap_find_free_region(rmi_vmid_bitmap, vmid_count, 0);
+	spin_unlock(&rmi_vmid_lock);
+
+	return ret;
+}
+
+static void rmi_vmid_release(unsigned int vmid)
+{
+	spin_lock(&rmi_vmid_lock);
+	bitmap_release_region(rmi_vmid_bitmap, vmid, 0);
+	spin_unlock(&rmi_vmid_lock);
+}
+
 static int realm_unmap_private_page(struct realm *realm,
 				    unsigned long ipa,
 				    unsigned long *next_addr)
@@ -903,6 +939,7 @@ static int realm_init_ipa_state(struct kvm *kvm,
 
 static int realm_ensure_created(struct kvm *kvm)
 {
+	struct realm *realm = &kvm->arch.realm;
 	int ret;
 
 	switch (kvm_realm_state(kvm)) {
@@ -916,7 +953,13 @@ static int realm_ensure_created(struct kvm *kvm)
 		return -EBUSY;
 	}
 
+	ret = rmi_vmid_reserve();
+	if (ret < 0)
+		return ret;
+	realm->vmid = ret;
 	ret = realm_create_rd(kvm);
+	if (ret)
+		rmi_vmid_release(realm->vmid);
 	return ret;
 }
 
@@ -1307,6 +1350,8 @@ void kvm_destroy_realm(struct kvm *kvm)
 		realm->rd = NULL;
 	}
 
+	rmi_vmid_release(realm->vmid);
+
 	for (i = 0; i < pgd_size; i += RMM_PAGE_SIZE) {
 		phys_addr_t pgd_phys = kvm->arch.mmu.pgd_phys + i;
 
@@ -1342,5 +1387,8 @@ void kvm_init_rmi(void)
 	if (WARN_ON(rmi_features(0, &rmm_feat_reg0)))
 		return;
 
+	if (rmi_vmid_init())
+		return;
+
 	/* Future patch will enable static branch kvm_rmi_is_available */
 }
-- 
2.43.0