[PATCH v11 42/43] KVM: arm64: nv: Accelerate EL0 timer read accesses when FEAT_ECV is on

[Marc Zyngier]

Although FEAT_ECV allows us to correctly enable the timers, it also
reduces performances pretty badly (a L2 guest doing a lot of virtio
emulated in L1 userspace results in a 30% degradation).

Mitigate this by emulating the CTL/CVAL register reads in the
inner run loop, without returning to the general kernel. This halves
the overhead described above.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/arch_timer.c     | 15 -------
 arch/arm64/kvm/hyp/vhe/switch.c | 70 +++++++++++++++++++++++++++++++++
 include/kvm/arm_arch_timer.h    | 15 +++++++
 3 files changed, 85 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 860f6e190e63..1ee1ede23607 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -101,21 +101,6 @@ u64 timer_get_cval(struct arch_timer_context *ctxt)
 	}
 }
 
-static u64 timer_get_offset(struct arch_timer_context *ctxt)
-{
-	u64 offset = 0;
-
-	if (!ctxt)
-		return 0;
-
-	if (ctxt->offset.vm_offset)
-		offset += *ctxt->offset.vm_offset;
-	if (ctxt->offset.vcpu_offset)
-		offset += *ctxt->offset.vcpu_offset;
-
-	return offset;
-}
-
 static void timer_set_ctl(struct arch_timer_context *ctxt, u32 ctl)
 {
 	struct kvm_vcpu *vcpu = ctxt->vcpu;
diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index 360328aaaf7c..8d1e9d1adabe 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -258,11 +258,81 @@ static bool kvm_hyp_handle_tlbi_el1(struct kvm_vcpu *vcpu, u64 *exit_code)
 	return true;
 }
 
+static bool kvm_hyp_handle_timer(struct kvm_vcpu *vcpu, u64 *exit_code)
+{
+	u64 esr, val;
+
+	/*
+	 * Having FEAT_ECV allows for a better quality of timer emulation.
+	 * However, this comes at a huge cost in terms of traps. Try and
+	 * satisfy the reads without returning to the kernel if we can.
+	 */
+	if (!is_hyp_ctxt(vcpu))
+		return false;
+
+	esr = kvm_vcpu_get_esr(vcpu);
+	if ((esr & ESR_ELx_SYS64_ISS_DIR_MASK) != ESR_ELx_SYS64_ISS_DIR_READ)
+		return false;
+
+	switch (esr_sys64_to_sysreg(esr)) {
+	case SYS_CNTP_CTL_EL02:
+		val = __vcpu_sys_reg(vcpu, CNTP_CTL_EL0);
+		break;
+	case SYS_CNTP_CTL_EL0:
+		if (vcpu_el2_e2h_is_set(vcpu))
+			val = read_sysreg_el0(SYS_CNTP_CTL);
+		else
+			val = __vcpu_sys_reg(vcpu, CNTP_CTL_EL0);
+		break;
+	case SYS_CNTP_CVAL_EL02:
+		val = __vcpu_sys_reg(vcpu, CNTP_CVAL_EL0);
+		break;
+	case SYS_CNTP_CVAL_EL0:
+		if (vcpu_el2_e2h_is_set(vcpu)) {
+			val = read_sysreg_el0(SYS_CNTP_CVAL);
+
+			if (!has_cntpoff())
+				val -= timer_get_offset(vcpu_hptimer(vcpu));
+		} else {
+			val = __vcpu_sys_reg(vcpu, CNTP_CVAL_EL0);
+		}
+		break;
+	case SYS_CNTV_CTL_EL02:
+		val = __vcpu_sys_reg(vcpu, CNTV_CTL_EL0);
+		break;
+	case SYS_CNTV_CTL_EL0:
+		if (vcpu_el2_e2h_is_set(vcpu))
+			val = read_sysreg_el0(SYS_CNTV_CTL);
+		else
+			val = __vcpu_sys_reg(vcpu, CNTV_CTL_EL0);
+		break;
+	case SYS_CNTV_CVAL_EL02:
+		val = __vcpu_sys_reg(vcpu, CNTV_CVAL_EL0);
+		break;
+	case SYS_CNTV_CVAL_EL0:
+		if (vcpu_el2_e2h_is_set(vcpu))
+			val = read_sysreg_el0(SYS_CNTV_CVAL);
+		else
+			val = __vcpu_sys_reg(vcpu, CNTV_CVAL_EL0);
+		break;
+	default:
+		return false;
+	}
+
+	vcpu_set_reg(vcpu, kvm_vcpu_sys_get_rt(vcpu), val);
+	__kvm_skip_instr(vcpu);
+
+	return true;
+}
+
 static bool kvm_hyp_handle_sysreg_vhe(struct kvm_vcpu *vcpu, u64 *exit_code)
 {
 	if (kvm_hyp_handle_tlbi_el1(vcpu, exit_code))
 		return true;
 
+	if (kvm_hyp_handle_timer(vcpu, exit_code))
+		return true;
+
 	return kvm_hyp_handle_sysreg(vcpu, exit_code);
 }
 
diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
index 6e3f6b7ff2b2..c1ba31fab6f5 100644
--- a/include/kvm/arm_arch_timer.h
+++ b/include/kvm/arm_arch_timer.h
@@ -156,4 +156,19 @@ static inline bool has_cntpoff(void)
 	return (has_vhe() && cpus_have_final_cap(ARM64_HAS_ECV_CNTPOFF));
 }
 
+static inline u64 timer_get_offset(struct arch_timer_context *ctxt)
+{
+	u64 offset = 0;
+
+	if (!ctxt)
+		return 0;
+
+	if (ctxt->offset.vm_offset)
+		offset += *ctxt->offset.vm_offset;
+	if (ctxt->offset.vcpu_offset)
+		offset += *ctxt->offset.vcpu_offset;
+
+	return offset;
+}
+
 #endif
-- 
2.39.2