[PATCH v2 2/3] KVM: arm64: Plumb cp10 ID traps through the AArch64 sysreg handler

[Oliver Upton]

In order to enable HCR_EL2.TID3 for AArch32 guests KVM needs to handle
traps where ESR_EL2.EC=0x8, which corresponds to an attempted VMRS
access from an ID group register. Specifically, the MVFR{0-2} registers
are accessed this way from AArch32. Conveniently, these registers are
architecturally mapped to MVFR{0-2}_EL1 in AArch64. Furthermore, KVM
already handles reads to these aliases in AArch64.

Plumb VMRS read traps through to the general AArch64 system register
handler.

Signed-off-by: Oliver Upton <oupton at google.com>
---
 arch/arm64/include/asm/kvm_host.h |  1 +
 arch/arm64/kvm/handle_exit.c      |  1 +
 arch/arm64/kvm/sys_regs.c         | 61 +++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 0e96087885fe..7a65ac268a22 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -673,6 +673,7 @@ int kvm_handle_cp14_64(struct kvm_vcpu *vcpu);
 int kvm_handle_cp15_32(struct kvm_vcpu *vcpu);
 int kvm_handle_cp15_64(struct kvm_vcpu *vcpu);
 int kvm_handle_sys_reg(struct kvm_vcpu *vcpu);
+int kvm_handle_cp10_id(struct kvm_vcpu *vcpu);
 
 void kvm_reset_sys_regs(struct kvm_vcpu *vcpu);
 
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 97fe14aab1a3..5088a86ace5b 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -167,6 +167,7 @@ static exit_handle_fn arm_exit_handlers[] = {
 	[ESR_ELx_EC_CP15_64]	= kvm_handle_cp15_64,
 	[ESR_ELx_EC_CP14_MR]	= kvm_handle_cp14_32,
 	[ESR_ELx_EC_CP14_LS]	= kvm_handle_cp14_load_store,
+	[ESR_ELx_EC_CP10_ID]	= kvm_handle_cp10_id,
 	[ESR_ELx_EC_CP14_64]	= kvm_handle_cp14_64,
 	[ESR_ELx_EC_HVC32]	= handle_hvc,
 	[ESR_ELx_EC_SMC32]	= handle_smc,
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 8b791256a5b4..4863592d060d 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2341,6 +2341,67 @@ static int kvm_handle_cp_64(struct kvm_vcpu *vcpu,
 
 static int emulate_sys_reg(struct kvm_vcpu *vcpu, struct sys_reg_params *params);
 
+/*
+ * The CP10 ID registers are architecturally mapped to AArch64 feature
+ * registers. Abuse that fact so we can rely on the AArch64 handler for accesses
+ * from AArch32.
+ */
+static bool kvm_esr_cp10_id_to_sys64(u32 esr, struct sys_reg_params *params)
+{
+	params->is_write = ((esr & 1) == 0);
+	params->Op0 = 3;
+	params->Op1 = 0;
+	params->CRn = 0;
+	params->CRm = 3;
+
+	switch ((esr >> 10) & 0xf) {
+	/* MVFR0 */
+	case 0b0111:
+		params->Op2 = 0;
+		break;
+	/* MVFR1 */
+	case 0b0110:
+		params->Op2 = 1;
+		break;
+	/* MVFR2 */
+	case 0b0101:
+		params->Op2 = 2;
+		break;
+	default:
+		return false;
+	}
+
+	return true;
+}
+
+/**
+ * kvm_handle_cp10_id() - Handles a VMRS trap on guest access to a 'Media and
+ *			  VFP Register' from AArch32.
+ * @vcpu: The vCPU pointer
+ *
+ * MVFR{0-2} are architecturally mapped to the AArch64 MVFR{0-2}_EL1 registers.
+ * Work out the correct AArch64 system register encoding and reroute to the
+ * AArch64 system register emulation.
+ */
+int kvm_handle_cp10_id(struct kvm_vcpu *vcpu)
+{
+	int Rt = kvm_vcpu_sys_get_rt(vcpu);
+	u32 esr = kvm_vcpu_get_esr(vcpu);
+	struct sys_reg_params params;
+	int ret;
+
+	/* UNDEF on any unhandled register or an attempted write */
+	if (!kvm_esr_cp10_id_to_sys64(esr, &params) || params.is_write) {
+		kvm_inject_undefined(vcpu);
+		return 1;
+	}
+
+	ret = emulate_sys_reg(vcpu, &params);
+
+	vcpu_set_reg(vcpu, Rt, params.regval);
+	return ret;
+}
+
 /**
  * kvm_emulate_cp15_id_reg() - Handles an MRC trap on a guest CP15 access where
  *			       CRn=0, which corresponds to the AArch32 feature
-- 
2.35.1.1094.g7c7d902a7c-goog