KVM: arm64: Hide TCR2_EL1 from userspace when disabled for guests

When the guest does not support FEAT_TCR2 we should not allow any access
to it in order to ensure that we do not create spurious issues with guest
migration. Add a visibility operation for it.

Fixes: fbff560 ("KVM: arm64: Save/restore TCR2_EL1")
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240822-kvm-arm64-hide-pie-regs-v2-2-376624fa829c@kernel.org
[maz: simplify by using __el2_visibility(), kvm_has_tcr2() throughout]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241023145345.1613824-25-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: broonie

arch/arm64/include/asm/kvm_host.h

@@ -1519,4 +1519,7 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
 	(system_supports_fpmr() &&			\
 	 kvm_has_feat((k), ID_AA64PFR2_EL1, FPMR, IMP))
 
+#define kvm_has_tcr2(k)				\
+	(kvm_has_feat((k), ID_AA64MMFR3_EL1, TCRX, IMP))
+
 #endif /* __ARM64_KVM_HOST_H__ */

arch/arm64/kvm/at.c

@@ -1099,7 +1099,7 @@ static u64 __kvm_at_s1e01_fast(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
 	write_sysreg_el1(vcpu_read_sys_reg(vcpu, TTBR1_EL1),	SYS_TTBR1);
 	write_sysreg_el1(vcpu_read_sys_reg(vcpu, TCR_EL1),	SYS_TCR);
 	write_sysreg_el1(vcpu_read_sys_reg(vcpu, MAIR_EL1),	SYS_MAIR);
-	if (kvm_has_feat(vcpu->kvm, ID_AA64MMFR3_EL1, TCRX, IMP)) {
+	if (kvm_has_tcr2(vcpu->kvm)) {
 		write_sysreg_el1(vcpu_read_sys_reg(vcpu, TCR2_EL1), SYS_TCR2);
 		if (kvm_has_feat(vcpu->kvm, ID_AA64MMFR3_EL1, S1PIE, IMP)) {
 			write_sysreg_el1(vcpu_read_sys_reg(vcpu, PIR_EL1), SYS_PIR);

arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h

@@ -69,7 +69,7 @@ static inline bool ctxt_has_tcrx(struct kvm_cpu_context *ctxt)
 		return false;
 
 	vcpu = ctxt_to_vcpu(ctxt);
-	return kvm_has_feat(kern_hyp_va(vcpu->kvm), ID_AA64MMFR3_EL1, TCRX, IMP);
+	return kvm_has_tcr2(kern_hyp_va(vcpu->kvm));
 }
 
 static inline bool ctxt_has_s1poe(struct kvm_cpu_context *ctxt)

arch/arm64/kvm/nested.c

@@ -1054,7 +1054,7 @@ int kvm_init_nv_sysregs(struct kvm *kvm)
 		res0 |= HCRX_EL2_PTTWI;
 	if (!kvm_has_feat(kvm, ID_AA64MMFR3_EL1, SCTLRX, IMP))
 		res0 |= HCRX_EL2_SCTLR2En;
-	if (!kvm_has_feat(kvm, ID_AA64MMFR3_EL1, TCRX, IMP))
+	if (!kvm_has_tcr2(kvm))
 		res0 |= HCRX_EL2_TCR2En;
 	if (!kvm_has_feat(kvm, ID_AA64ISAR2_EL1, MOPS, IMP))
 		res0 |= (HCRX_EL2_MSCEn | HCRX_EL2_MCE2);

arch/arm64/kvm/sys_regs.c

@@ -446,7 +446,7 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
 	u64 val, mask, shift;
 
 	if (reg_to_encoding(r) == SYS_TCR2_EL1 &&
-	    !kvm_has_feat(vcpu->kvm, ID_AA64MMFR3_EL1, TCRX, IMP))
+	    !kvm_has_tcr2(vcpu->kvm))
 		return undef_access(vcpu, p, r);
 
 	BUG_ON(!p->is_write);
@@ -471,7 +471,7 @@ static bool access_tcr2_el2(struct kvm_vcpu *vcpu,
 			    struct sys_reg_params *p,
 			    const struct sys_reg_desc *r)
 {
-	if (!kvm_has_feat(vcpu->kvm, ID_AA64MMFR3_EL1, TCRX, IMP)) {
+	if (!kvm_has_tcr2(vcpu->kvm)) {
 		kvm_inject_undefined(vcpu);
 		return false;
 	}
@@ -2357,6 +2357,21 @@ static unsigned int s1poe_visibility(const struct kvm_vcpu *vcpu,
 	return REG_HIDDEN;
 }
 
+static unsigned int tcr2_visibility(const struct kvm_vcpu *vcpu,
+				    const struct sys_reg_desc *rd)
+{
+	if (kvm_has_tcr2(vcpu->kvm))
+		return 0;
+
+	return REG_HIDDEN;
+}
+
+static unsigned int tcr2_el2_visibility(const struct kvm_vcpu *vcpu,
+				    const struct sys_reg_desc *rd)
+{
+	return __el2_visibility(vcpu, rd, tcr2_visibility);
+}
+
 /*
  * Architected system registers.
  * Important: Must be sorted ascending by Op0, Op1, CRn, CRm, Op2
@@ -2567,7 +2582,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_TTBR0_EL1), access_vm_reg, reset_unknown, TTBR0_EL1 },
 	{ SYS_DESC(SYS_TTBR1_EL1), access_vm_reg, reset_unknown, TTBR1_EL1 },
 	{ SYS_DESC(SYS_TCR_EL1), access_vm_reg, reset_val, TCR_EL1, 0 },
-	{ SYS_DESC(SYS_TCR2_EL1), access_vm_reg, reset_val, TCR2_EL1, 0 },
+	{ SYS_DESC(SYS_TCR2_EL1), access_vm_reg, reset_val, TCR2_EL1, 0,
+	  .visibility = tcr2_visibility },
 
 	PTRAUTH_KEY(APIA),
 	PTRAUTH_KEY(APIB),
@@ -2904,7 +2920,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	EL2_REG(TTBR0_EL2, access_rw, reset_val, 0),
 	EL2_REG(TTBR1_EL2, access_rw, reset_val, 0),
 	EL2_REG(TCR_EL2, access_rw, reset_val, TCR_EL2_RES1),
-	EL2_REG(TCR2_EL2, access_tcr2_el2, reset_val, TCR2_EL2_RES1),
+	EL2_REG_FILTERED(TCR2_EL2, access_tcr2_el2, reset_val, TCR2_EL2_RES1,
+			 tcr2_el2_visibility),
 	EL2_REG_VNCR(VTTBR_EL2, reset_val, 0),
 	EL2_REG_VNCR(VTCR_EL2, reset_val, 0),
 
@@ -4800,7 +4817,7 @@ void kvm_calculate_traps(struct kvm_vcpu *vcpu)
 		if (kvm_has_feat(kvm, ID_AA64ISAR2_EL1, MOPS, IMP))
 			vcpu->arch.hcrx_el2 |= (HCRX_EL2_MSCEn | HCRX_EL2_MCE2);
 
-		if (kvm_has_feat(kvm, ID_AA64MMFR3_EL1, TCRX, IMP))
+		if (kvm_has_tcr2(kvm))
 			vcpu->arch.hcrx_el2 |= HCRX_EL2_TCR2En;
 
 		if (kvm_has_fpmr(kvm))