[PATCH 05/15] KVM: arm64: Evaluate debug owner at vcpu_load()

[Oliver Upton <oliver.upton@linux.dev>]

In preparation for tossing the debug_ptr mess, introduce an enumeration
to track the ownership of the debug registers while in the guest. Update
the owner at vcpu_load() based on whether the host needs to steal the
guest's debug context or if breakpoints/watchpoints are actively in use.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_host.h | 10 ++++++++++
 arch/arm64/kvm/arm.c              |  1 +
 arch/arm64/kvm/debug.c            | 23 +++++++++++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index cf5cdc468aa4..f954b082dc4f 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -756,6 +756,12 @@ struct kvm_vcpu_arch {
 	struct kvm_guest_debug_arch vcpu_debug_state;
 	struct kvm_guest_debug_arch external_debug_state;
 
+	enum {
+		VCPU_DEBUG_FREE,
+		VCPU_DEBUG_HOST_OWNED,
+		VCPU_DEBUG_GUEST_OWNED,
+	} debug_owner;
+
 	/* VGIC state */
 	struct vgic_cpu vgic_cpu;
 	struct arch_timer_cpu timer_cpu;
@@ -1345,10 +1351,14 @@ void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu);
 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu);
 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu);
+void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu);
 
 #define kvm_vcpu_os_lock_enabled(vcpu)		\
 	(!!(__vcpu_sys_reg(vcpu, OSLSR_EL1) & OSLSR_EL1_OSLK))
 
+#define kvm_host_owns_debug_regs(vcpu)		\
+	((vcpu)->arch.debug_owner == VCPU_DEBUG_HOST_OWNED)
+
 int kvm_arm_vcpu_arch_set_attr(struct kvm_vcpu *vcpu,
 			       struct kvm_device_attr *attr);
 int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 3822774840e1..a068337da52a 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -598,6 +598,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
 	kvm_vgic_load(vcpu);
 	kvm_timer_vcpu_load(vcpu);
+	kvm_vcpu_load_debug(vcpu);
 	if (has_vhe())
 		kvm_vcpu_load_vhe(vcpu);
 	kvm_arch_vcpu_load_fp(vcpu);
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 97d0c6fd5f61..e2798a4eec47 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -313,3 +313,26 @@ void kvm_init_host_debug_data(void)
 	    !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
 		host_data_set_flag(HAS_TRBE);
 }
+
+void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu)
+{
+	u64 mdscr;
+
+	/* Must be called before kvm_vcpu_load_vhe() */
+	KVM_BUG_ON(vcpu_get_flag(vcpu, SYSREGS_ON_CPU), vcpu->kvm);
+
+	if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
+		vcpu->arch.debug_owner = VCPU_DEBUG_HOST_OWNED;
+	} else {
+		mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
+
+		/*
+		 * Eagerly restore the debug state if the debugger is actively
+		 * in use
+		 */
+		if (mdscr & (MDSCR_EL1_KDE | MDSCR_EL1_MDE))
+			vcpu->arch.debug_owner = VCPU_DEBUG_GUEST_OWNED;
+		else
+			vcpu->arch.debug_owner = VCPU_DEBUG_FREE;
+	}
+}
-- 
2.39.5