KVM: arm64: Parametrize exception entry with a target EL

We currently assume that an exception is delivered to EL1, always.
Once we emulate EL2, this no longer will be the case. To prepare
for this, add a target_mode parameter.

While we're at it, merge the computing of the target PC and PSTATE in
a single function that updates both PC and CPSR after saving their
previous values in the corresponding ELR/SPSR. This ensures that they
are updated in the correct order (a pretty common source of bugs...).

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/ptrace.h

@@ -35,6 +35,7 @@
 #define GIC_PRIO_PSR_I_SET		(1 << 4)
 
 /* Additional SPSR bits not exposed in the UABI */
+#define PSR_MODE_THREAD_BIT	(1 << 0)
 #define PSR_IL_BIT		(1 << 20)
 
 /* AArch32-specific ptrace requests */

arch/arm64/kvm/inject_fault.c

@@ -26,28 +26,12 @@ enum exception_type {
 	except_type_serror	= 0x180,
 };
 
-static u64 get_except_vector(struct kvm_vcpu *vcpu, enum exception_type type)
-{
-	u64 exc_offset;
-
-	switch (*vcpu_cpsr(vcpu) & (PSR_MODE_MASK | PSR_MODE32_BIT)) {
-	case PSR_MODE_EL1t:
-		exc_offset = CURRENT_EL_SP_EL0_VECTOR;
-		break;
-	case PSR_MODE_EL1h:
-		exc_offset = CURRENT_EL_SP_ELx_VECTOR;
-		break;
-	case PSR_MODE_EL0t:
-		exc_offset = LOWER_EL_AArch64_VECTOR;
-		break;
-	default:
-		exc_offset = LOWER_EL_AArch32_VECTOR;
-	}
-
-	return vcpu_read_sys_reg(vcpu, VBAR_EL1) + exc_offset + type;
-}
-
 /*
+ * This performs the exception entry at a given EL (@target_mode), stashing PC
+ * and PSTATE into ELR and SPSR respectively, and compute the new PC/PSTATE.
+ * The EL passed to this function *must* be a non-secure, privileged mode with
+ * bit 0 being set (PSTATE.SP == 1).
+ *
  * When an exception is taken, most PSTATE fields are left unchanged in the
  * handler. However, some are explicitly overridden (e.g. M[4:0]). Luckily all
  * of the inherited bits have the same position in the AArch64/AArch32 SPSR_ELx
@@ -59,10 +43,35 @@ static u64 get_except_vector(struct kvm_vcpu *vcpu, enum exception_type type)
  * Here we manipulate the fields in order of the AArch64 SPSR_ELx layout, from
  * MSB to LSB.
  */
-static unsigned long get_except64_pstate(struct kvm_vcpu *vcpu)
+static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
+			      enum exception_type type)
 {
-	unsigned long sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL1);
-	unsigned long old, new;
+	unsigned long sctlr, vbar, old, new, mode;
+	u64 exc_offset;
+
+	mode = *vcpu_cpsr(vcpu) & (PSR_MODE_MASK | PSR_MODE32_BIT);
+
+	if      (mode == target_mode)
+		exc_offset = CURRENT_EL_SP_ELx_VECTOR;
+	else if ((mode | PSR_MODE_THREAD_BIT) == target_mode)
+		exc_offset = CURRENT_EL_SP_EL0_VECTOR;
+	else if (!(mode & PSR_MODE32_BIT))
+		exc_offset = LOWER_EL_AArch64_VECTOR;
+	else
+		exc_offset = LOWER_EL_AArch32_VECTOR;
+
+	switch (target_mode) {
+	case PSR_MODE_EL1h:
+		vbar = vcpu_read_sys_reg(vcpu, VBAR_EL1);
+		sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL1);
+		vcpu_write_elr_el1(vcpu, *vcpu_pc(vcpu));
+		break;
+	default:
+		/* Don't do that */
+		BUG();
+	}
+
+	*vcpu_pc(vcpu) = vbar + exc_offset + type;
 
 	old = *vcpu_cpsr(vcpu);
 	new = 0;
@@ -105,9 +114,10 @@ static unsigned long get_except64_pstate(struct kvm_vcpu *vcpu)
 	new |= PSR_I_BIT;
 	new |= PSR_F_BIT;
 
-	new |= PSR_MODE_EL1h;
+	new |= target_mode;
 
-	return new;
+	*vcpu_cpsr(vcpu) = new;
+	vcpu_write_spsr(vcpu, old);
 }
 
 static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr)
@@ -116,11 +126,7 @@ static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr
 	bool is_aarch32 = vcpu_mode_is_32bit(vcpu);
 	u32 esr = 0;
 
-	vcpu_write_elr_el1(vcpu, *vcpu_pc(vcpu));
-	*vcpu_pc(vcpu) = get_except_vector(vcpu, except_type_sync);
-
-	*vcpu_cpsr(vcpu) = get_except64_pstate(vcpu);
-	vcpu_write_spsr(vcpu, cpsr);
+	enter_exception64(vcpu, PSR_MODE_EL1h, except_type_sync);
 
 	vcpu_write_sys_reg(vcpu, addr, FAR_EL1);
 
@@ -148,14 +154,9 @@ static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr
 
 static void inject_undef64(struct kvm_vcpu *vcpu)
 {
-	unsigned long cpsr = *vcpu_cpsr(vcpu);
 	u32 esr = (ESR_ELx_EC_UNKNOWN << ESR_ELx_EC_SHIFT);
 
-	vcpu_write_elr_el1(vcpu, *vcpu_pc(vcpu));
-	*vcpu_pc(vcpu) = get_except_vector(vcpu, except_type_sync);
-
-	*vcpu_cpsr(vcpu) = get_except64_pstate(vcpu);
-	vcpu_write_spsr(vcpu, cpsr);
+	enter_exception64(vcpu, PSR_MODE_EL1h, except_type_sync);
 
 	/*
 	 * Build an unknown exception, depending on the instruction