[PATCH v2 14/16] KVM: arm64: Hide TCR2_EL1 from userspace when disabled for guests

[Marc Zyngier <maz@kernel.org>]

From: Mark Brown <broonie@kernel.org>

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: fbff56068232 ("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
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/kvm_host.h |  3 +++
 arch/arm64/kvm/sys_regs.c         | 29 ++++++++++++++++++++++++++---
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index ab4c675b491d..7889e5f4009f 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -1476,4 +1476,7 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
 		(pa + pi + pa3) == 1;					\
 	})
 
+#define kvm_has_tcr2(k)				\
+	(kvm_has_feat((k), ID_AA64MMFR3_EL1, TCRX, IMP))
+
 #endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 4ee74e2d4f08..64562b0c2359 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2319,6 +2319,27 @@ static bool access_zcr_el2(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+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)
+{
+	unsigned int r;
+
+	r = el2_visibility(vcpu, rd);
+	if (r)
+		return r;
+
+	return tcr2_visibility(vcpu, rd);
+}
+
 /*
  * Architected system registers.
  * Important: Must be sorted ascending by Op0, Op1, CRn, CRm, Op2
@@ -2503,7 +2524,8 @@ 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),
@@ -2820,7 +2842,8 @@ 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),
 
@@ -4679,7 +4702,7 @@ 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;
 	}
 
-- 
2.39.2