[RFC 13/55] KVM: arm64: Handle eret instruction traps

[Jintack Lim]

When HCR.NV bit is set, eret instruction execution in the guest
hypervisor will trap with EC code 0x1A. Let ELR_EL2 and SPSR_EL2 state
from the guest's perspective be restored to the hardware on the next
guest entry.

Signed-off-by: Jintack Lim <jintack at cs.columbia.edu>
---
 arch/arm64/include/asm/esr.h |  1 +
 arch/arm64/kvm/handle_exit.c | 12 ++++++++++++
 arch/arm64/kvm/trace.h       | 21 +++++++++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index d14c478..f32e3a7 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -42,6 +42,7 @@
 #define ESR_ELx_EC_HVC64	(0x16)
 #define ESR_ELx_EC_SMC64	(0x17)
 #define ESR_ELx_EC_SYS64	(0x18)
+#define ESR_ELx_EC_ERET		(0x1A)
 /* Unallocated EC: 0x19 - 0x1E */
 #define ESR_ELx_EC_IMP_DEF	(0x1f)
 #define ESR_ELx_EC_IABT_LOW	(0x20)
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index a204adf..4e4a915 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -125,6 +125,17 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	return ret;
 }
 
+static int kvm_handle_eret(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+	trace_kvm_nested_eret(vcpu, vcpu_el2_reg(vcpu, ELR_EL2),
+			      vcpu_el2_reg(vcpu, SPSR_EL2));
+
+	*vcpu_pc(vcpu) = vcpu_el2_reg(vcpu, ELR_EL2);
+	*vcpu_cpsr(vcpu) = vcpu_el2_reg(vcpu, SPSR_EL2);
+
+	return 1;
+}
+
 static exit_handle_fn arm_exit_handlers[] = {
 	[ESR_ELx_EC_WFx]	= kvm_handle_wfx,
 	[ESR_ELx_EC_CP15_32]	= kvm_handle_cp15_32,
@@ -137,6 +148,7 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	[ESR_ELx_EC_HVC64]	= handle_hvc,
 	[ESR_ELx_EC_SMC64]	= handle_smc,
 	[ESR_ELx_EC_SYS64]	= kvm_handle_sys_reg,
+	[ESR_ELx_EC_ERET]	= kvm_handle_eret,
 	[ESR_ELx_EC_IABT_LOW]	= kvm_handle_guest_abort,
 	[ESR_ELx_EC_DABT_LOW]	= kvm_handle_guest_abort,
 	[ESR_ELx_EC_SOFTSTP_LOW]= kvm_handle_guest_debug,
diff --git a/arch/arm64/kvm/trace.h b/arch/arm64/kvm/trace.h
index 7c86cfb..5f40987 100644
--- a/arch/arm64/kvm/trace.h
+++ b/arch/arm64/kvm/trace.h
@@ -187,6 +187,27 @@
 	TP_printk("vcpu: %p, inject exception to vEL2: ESR_EL2 0x%lx, vector: 0x%016lx",
 		  __entry->vcpu, __entry->esr_el2, __entry->pc)
 );
+
+TRACE_EVENT(kvm_nested_eret,
+	TP_PROTO(struct kvm_vcpu *vcpu, unsigned long elr_el2,
+		 unsigned long spsr_el2),
+	TP_ARGS(vcpu, elr_el2, spsr_el2),
+
+	TP_STRUCT__entry(
+		__field(struct kvm_vcpu *,	vcpu)
+		__field(unsigned long,		elr_el2)
+		__field(unsigned long,		spsr_el2)
+	),
+
+	TP_fast_assign(
+		__entry->vcpu = vcpu;
+		__entry->elr_el2 = elr_el2;
+		__entry->spsr_el2 = spsr_el2;
+	),
+
+	TP_printk("vcpu: %p, eret to elr_el2: 0x%016lx, with spsr_el2: 0x%08lx",
+		  __entry->vcpu, __entry->elr_el2, __entry->spsr_el2)
+);
 #endif /* _TRACE_ARM64_KVM_H */
 
 #undef TRACE_INCLUDE_PATH
-- 
1.9.1