[PATCH v4 4/6] KVM: arm64: Add HDBSS per-vCPU buffer management
From: Tian Zheng
Date: Thu Jul 09 2026 - 07:07:26 EST
From: eillon <yezhenyu2@xxxxxxxxxx>
Add HDBSS (Hardware Dirty Bit State Structure) per-vCPU buffer
management including allocation, freeing, and loading of HDBSS
registers during vCPU load.
This patch creates the foundational infrastructure:
- struct vcpu_hdbss_state and enable_hdbss/hdbss_order in kvm_arch
- kvm_dirty_bit.h header with alloc/free declarations
- dirty_bit.c with alloc/free helpers
- __load_hdbss() in VHE switch for register loading
- vCPU create/destroy hooks for buffer lifecycle
- sysreg definitions for HDBSS register manipulation
- Makefile update for dirty_bit.o
Signed-off-by: Eillon <yezhenyu2@xxxxxxxxxx>
Signed-off-by: Tian Zheng <zhengtian10@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_dirty_bit.h | 16 ++++++++
arch/arm64/include/asm/kvm_host.h | 13 +++++++
arch/arm64/include/asm/sysreg.h | 11 ++++++
arch/arm64/kvm/Makefile | 1 +
arch/arm64/kvm/arm.c | 7 ++++
arch/arm64/kvm/dirty_bit.c | 52 ++++++++++++++++++++++++++
arch/arm64/kvm/hyp/vhe/switch.c | 15 ++++++++
arch/arm64/kvm/mmu.c | 1 +
arch/arm64/kvm/reset.c | 4 ++
9 files changed, 120 insertions(+)
create mode 100644 arch/arm64/include/asm/kvm_dirty_bit.h
create mode 100644 arch/arm64/kvm/dirty_bit.c
diff --git a/arch/arm64/include/asm/kvm_dirty_bit.h b/arch/arm64/include/asm/kvm_dirty_bit.h
new file mode 100644
index 000000000000..84b12f0a10af
--- /dev/null
+++ b/arch/arm64/include/asm/kvm_dirty_bit.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2026 ARM Ltd.
+ * Author: Leonardo Bras <leo.bras@xxxxxxx>
+ */
+
+#ifndef __ARM64_KVM_DIRTY_BIT_H__
+#define __ARM64_KVM_DIRTY_BIT_H__
+
+#include <asm/kvm_pgtable.h>
+#include <asm/sysreg.h>
+
+int kvm_arm_vcpu_alloc_hdbss(struct kvm_vcpu *vcpu, unsigned int order);
+void kvm_arm_vcpu_free_hdbss(struct kvm_vcpu *vcpu);
+
+#endif /* __ARM64_KVM_DIRTY_BIT_H__ */
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index bae2c4f92ef5..c41ec6d9c45a 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -420,6 +420,10 @@ struct kvm_arch {
*/
struct kvm_protected_vm pkvm;
+ /* HDBSS: per-VM dirty tracking state */
+ bool enable_hdbss;
+ unsigned int hdbss_order;
+
#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
/* Nested virtualization info */
struct dentry *debugfs_nv_dentry;
@@ -838,6 +842,12 @@ struct vcpu_reset_state {
bool reset;
};
+struct vcpu_hdbss_state {
+ phys_addr_t base_phys; /* for memory free */
+ u64 hdbssbr_el2; /* load directly */
+ u64 hdbssprod_el2; /* save directly */
+};
+
struct vncr_tlb;
struct kvm_vcpu_arch {
@@ -945,6 +955,9 @@ struct kvm_vcpu_arch {
/* Hyp-readable copy of kvm_vcpu::pid */
pid_t pid;
+
+ /* HDBSS registers info */
+ struct vcpu_hdbss_state hdbss;
};
/*
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 7aa08d59d494..1354a58c3316 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -1039,6 +1039,17 @@
#define GCS_CAP(x) ((((unsigned long)x) & GCS_CAP_ADDR_MASK) | \
GCS_CAP_VALID_TOKEN)
+
+/*
+ * Definitions for the HDBSS feature
+ */
+#define HDBSS_MAX_ORDER HDBSSBR_EL2_SZ_2MB
+
+#define HDBSSBR_EL2(baddr, sz) (((baddr) & HDBSSBR_EL2_BADDR_MASK) | \
+ FIELD_PREP(HDBSSBR_EL2_SZ_MASK, sz))
+
+#define HDBSSPROD_IDX(prod) FIELD_GET(HDBSSPROD_EL2_INDEX_MASK, prod)
+
/*
* Definitions for GICv5 instructions
*/
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 59612d2f277c..ec2749af64fa 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -18,6 +18,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
guest.o debug.o reset.o sys_regs.o stacktrace.o \
vgic-sys-reg-v3.o fpsimd.o pkvm.o \
arch_timer.o trng.o vmid.o emulate-nested.o nested.o at.o \
+ dirty_bit.o \
vgic/vgic.o vgic/vgic-init.o \
vgic/vgic-irqfd.o vgic/vgic-v2.o \
vgic/vgic-v3.o vgic/vgic-v4.o \
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 50adfff75be8..bf6688245d83 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -38,6 +38,7 @@
#include <asm/kvm_asm.h>
#include <asm/kvm_emulate.h>
#include <asm/kvm_hyp.h>
+#include <asm/kvm_dirty_bit.h>
#include <asm/kvm_mmu.h>
#include <asm/kvm_nested.h>
#include <asm/kvm_pkvm.h>
@@ -565,6 +566,12 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
if (err)
kvm_vgic_vcpu_destroy(vcpu);
+ if (vcpu->kvm->arch.enable_hdbss) {
+ err = kvm_arm_vcpu_alloc_hdbss(vcpu, vcpu->kvm->arch.hdbss_order);
+ if (err)
+ kvm_vgic_vcpu_destroy(vcpu);
+ }
+
return err;
}
diff --git a/arch/arm64/kvm/dirty_bit.c b/arch/arm64/kvm/dirty_bit.c
new file mode 100644
index 000000000000..6c7a6ef66b5a
--- /dev/null
+++ b/arch/arm64/kvm/dirty_bit.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2026 ARM Ltd.
+ * Author: Leonardo Bras <leo.bras@xxxxxxx>
+ */
+
+#include <asm/kvm_dirty_bit.h>
+#include <asm/kvm_mmu.h>
+#include <asm/sysreg.h>
+#include <linux/gfp.h>
+#include <linux/kconfig.h>
+#include <linux/mm.h>
+
+int kvm_arm_vcpu_alloc_hdbss(struct kvm_vcpu *vcpu, unsigned int order)
+{
+ struct page *hdbss_pg = NULL;
+
+ if (vcpu->arch.hdbss.hdbssbr_el2 || !system_supports_hdbss())
+ return 0;
+
+ if (order > HDBSS_MAX_ORDER)
+ return -EINVAL;
+
+ hdbss_pg = alloc_pages(GFP_KERNEL_ACCOUNT, order);
+ if (!hdbss_pg)
+ return -ENOMEM;
+
+ vcpu->arch.hdbss = (struct vcpu_hdbss_state) {
+ .base_phys = page_to_phys(hdbss_pg),
+ .hdbssbr_el2 = HDBSSBR_EL2(page_to_phys(hdbss_pg), order),
+ .hdbssprod_el2 = 0,
+ };
+
+ return 0;
+}
+
+void kvm_arm_vcpu_free_hdbss(struct kvm_vcpu *vcpu)
+{
+ struct page *hdbss_pg;
+
+ if (!vcpu->arch.hdbss.hdbssbr_el2) {
+ return;
+ }
+
+ hdbss_pg = phys_to_page(vcpu->arch.hdbss.base_phys);
+ if (hdbss_pg)
+ __free_pages(hdbss_pg,
+ FIELD_GET(HDBSSBR_EL2_SZ_MASK,
+ vcpu->arch.hdbss.hdbssbr_el2));
+
+ vcpu->arch.hdbss.hdbssbr_el2 = 0;
+}
diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index bbe9cebd3d9d..fe72944bfd3d 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -22,6 +22,7 @@
#include <asm/kvm_emulate.h>
#include <asm/kvm_hyp.h>
#include <asm/kvm_mmu.h>
+#include <asm/kvm_dirty_bit.h>
#include <asm/fpsimd.h>
#include <asm/debug-monitors.h>
#include <asm/processor.h>
@@ -213,6 +214,19 @@ static void __vcpu_put_deactivate_traps(struct kvm_vcpu *vcpu)
local_irq_restore(flags);
}
+static void __load_hdbss(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+
+ if (!kvm->arch.enable_hdbss)
+ return;
+
+ write_sysreg_s(vcpu->arch.hdbss.hdbssbr_el2, SYS_HDBSSBR_EL2);
+ write_sysreg_s(vcpu->arch.hdbss.hdbssprod_el2, SYS_HDBSSPROD_EL2);
+
+ isb();
+}
+
void kvm_vcpu_load_vhe(struct kvm_vcpu *vcpu)
{
host_data_ptr(host_ctxt)->__hyp_running_vcpu = vcpu;
@@ -220,6 +234,7 @@ void kvm_vcpu_load_vhe(struct kvm_vcpu *vcpu)
__vcpu_load_switch_sysregs(vcpu);
__vcpu_load_activate_traps(vcpu);
__load_stage2(vcpu->arch.hw_mmu);
+ __load_hdbss(vcpu);
}
void kvm_vcpu_put_vhe(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 346efed6e605..83251d95bf3f 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -16,6 +16,7 @@
#include <asm/cacheflush.h>
#include <asm/kvm_arm.h>
#include <asm/kvm_mmu.h>
+#include <asm/kvm_dirty_bit.h>
#include <asm/kvm_pgtable.h>
#include <asm/kvm_pkvm.h>
#include <asm/kvm_asm.h>
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index b963fd975aac..d8104bcbd9ff 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -27,6 +27,7 @@
#include <asm/kvm_asm.h>
#include <asm/kvm_emulate.h>
#include <asm/kvm_mmu.h>
+#include <asm/kvm_dirty_bit.h>
#include <asm/kvm_nested.h>
#include <asm/virt.h>
@@ -161,6 +162,9 @@ void kvm_arm_vcpu_destroy(struct kvm_vcpu *vcpu)
free_page((unsigned long)vcpu->arch.ctxt.vncr_array);
kfree(vcpu->arch.vncr_tlb);
kfree(vcpu->arch.ccsidr);
+
+ if (vcpu->kvm->arch.enable_hdbss)
+ kvm_arm_vcpu_free_hdbss(vcpu);
}
static void kvm_vcpu_reset_sve(struct kvm_vcpu *vcpu)
--
2.33.0