KVM: arm64: Move SPE availability check to VCPU load

At the moment, we check the availability of SPE on the given
CPU (i.e, SPE is implemented and is allowed at the host) during
every guest entry. This can be optimized a bit by moving the
check to vcpu_load time and recording the availability of the
feature on the current CPU via a new flag. This will also be useful
for adding the TRBE support.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Alexandru Elisei <Alexandru.Elisei@arm.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210405164307.1720226-7-suzuki.poulose@arm.comSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

arch/arm64/include/asm/kvm_host.h

@@ -400,6 +400,7 @@ struct kvm_vcpu_arch {
 #define KVM_ARM64_GUEST_HAS_PTRAUTH	(1 << 7) /* PTRAUTH exposed to guest */
 #define KVM_ARM64_PENDING_EXCEPTION	(1 << 8) /* Exception pending */
 #define KVM_ARM64_EXCEPT_MASK		(7 << 9) /* Target EL/MODE */
+#define KVM_ARM64_DEBUG_STATE_SAVE_SPE	(1 << 12) /* Save SPE context if active  */
 
 /*
  * When KVM_ARM64_PENDING_EXCEPTION is set, KVM_ARM64_EXCEPT_MASK can
@@ -734,6 +735,10 @@ static inline bool kvm_pmu_counter_deferred(struct perf_event_attr *attr)
 	return (!has_vhe() && attr->exclude_host);
 }
 
+/* Flags for host debug state */
+void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu);
+void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu);
+
 #ifdef CONFIG_KVM /* Avoid conflicts with core headers if CONFIG_KVM=n */
 static inline int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
 {

arch/arm64/kvm/arm.c

@@ -416,10 +416,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
 	if (vcpu_has_ptrauth(vcpu))
 		vcpu_ptrauth_disable(vcpu);
+	kvm_arch_vcpu_load_debug_state_flags(vcpu);
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
+	kvm_arch_vcpu_put_debug_state_flags(vcpu);
 	kvm_arch_vcpu_put_fp(vcpu);
 	if (has_vhe())
 		kvm_vcpu_put_sysregs_vhe(vcpu);

arch/arm64/kvm/debug.c

@@ -231,3 +231,26 @@ void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
 		}
 	}
 }
+
+void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
+{
+	u64 dfr0;
+
+	/* For VHE, there is nothing to do */
+	if (has_vhe())
+		return;
+
+	dfr0 = read_sysreg(id_aa64dfr0_el1);
+	/*
+	 * If SPE is present on this CPU and is available at current EL,
+	 * we may need to check if the host state needs to be saved.
+	 */
+	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_PMSVER_SHIFT) &&
+	    !(read_sysreg_s(SYS_PMBIDR_EL1) & BIT(SYS_PMBIDR_EL1_P_SHIFT)))
+		vcpu->arch.flags |= KVM_ARM64_DEBUG_STATE_SAVE_SPE;
+}
+
+void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.flags &= ~KVM_ARM64_DEBUG_STATE_SAVE_SPE;
+}

arch/arm64/kvm/hyp/nvhe/debug-sr.c

@@ -21,17 +21,11 @@ static void __debug_save_spe(u64 *pmscr_el1)
 	/* Clear pmscr in case of early return */
 	*pmscr_el1 = 0;
 
-	/* SPE present on this CPU? */
-	if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1),
-						  ID_AA64DFR0_PMSVER_SHIFT))
-		return;
-
-	/* Yes; is it owned by EL3? */
-	reg = read_sysreg_s(SYS_PMBIDR_EL1);
-	if (reg & BIT(SYS_PMBIDR_EL1_P_SHIFT))
-		return;
-
-	/* No; is the host actually using the thing? */
+	/*
+	 * At this point, we know that this CPU implements
+	 * SPE and is available to the host.
+	 * Check if the host is actually using it ?
+	 */
 	reg = read_sysreg_s(SYS_PMBLIMITR_EL1);
 	if (!(reg & BIT(SYS_PMBLIMITR_EL1_E_SHIFT)))
 		return;
@@ -61,7 +55,8 @@ static void __debug_restore_spe(u64 pmscr_el1)
 void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
 {
 	/* Disable and flush SPE data generation */
-	__debug_save_spe(&vcpu->arch.host_debug_state.pmscr_el1);
+	if (vcpu->arch.flags & KVM_ARM64_DEBUG_STATE_SAVE_SPE)
+		__debug_save_spe(&vcpu->arch.host_debug_state.pmscr_el1);
 }
 
 void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
@@ -71,7 +66,8 @@ void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
 
 void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu)
 {
-	__debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
+	if (vcpu->arch.flags & KVM_ARM64_DEBUG_STATE_SAVE_SPE)
+		__debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
 }
 
 void __debug_switch_to_host(struct kvm_vcpu *vcpu)