[PATCH v2 2/4] KVM: arm64: Allow userspace to change REVIDR_EL1

[Sebastian Ott]

Enable VMMs to write REVIDR_EL1 by treating it as a VM ID register.
Trap guest access of REVIDR_EL1 when the VMs value differs from hardware.

Signed-off-by: Sebastian Ott <sebott@xxxxxxxxxx>
---
 arch/arm64/include/asm/kvm_host.h |  3 +++
 arch/arm64/kvm/sys_regs.c         | 11 ++++++++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 3db8c773339e..c8fba4111b77 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -374,6 +374,7 @@ struct kvm_arch {
 	u64 id_regs[KVM_ARM_ID_REG_NUM];
 
 	u64 midr_el1;
+	u64 revidr_el1;
 	u64 ctr_el0;
 
 	/* Masks for VNCR-backed and general EL2 sysregs */
@@ -1472,6 +1473,8 @@ static inline u64 *__vm_id_reg(struct kvm_arch *ka, u32 reg)
 		return &ka->id_regs[IDREG_IDX(reg)];
 	case SYS_MIDR_EL1:
 		return &ka->midr_el1;
+	case SYS_REVIDR_EL1:
+		return &ka->revidr_el1;
 	case SYS_CTR_EL0:
 		return &ka->ctr_el0;
 	default:
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 7e1c9884f62a..646c0a04e58a 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1666,7 +1666,8 @@ static bool is_feature_id_reg(u32 encoding)
  */
 static inline bool is_vm_ftr_id_reg(u32 id)
 {
-	if (id == SYS_CTR_EL0 || id == SYS_MIDR_EL1)
+	if (id == SYS_CTR_EL0 || id == SYS_MIDR_EL1 ||
+	    id == SYS_REVIDR_EL1)
 		return true;
 
 	return (sys_reg_Op0(id) == 3 && sys_reg_Op1(id) == 0 &&
@@ -2542,6 +2543,7 @@ static bool access_mdcr(struct kvm_vcpu *vcpu,
 	}
 
 FUNCTION_RESET(midr_el1)
+FUNCTION_RESET(revidr_el1)
 
 
 /*
@@ -2595,6 +2597,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ ID_DESC(MIDR_EL1), .set_user = set_id_reg_non_ftr, .visibility = id_visibility,
 	  .reset = reset_midr_el1, .val = GENMASK_ULL(31, 0) },
 	{ SYS_DESC(SYS_MPIDR_EL1), NULL, reset_mpidr, MPIDR_EL1 },
+	{ ID_DESC(REVIDR_EL1), .set_user = set_id_reg_non_ftr, .visibility = id_visibility,
+	  .reset = reset_revidr_el1, .val = -1ULL },
 
 	/*
 	 * ID regs: all ID_SANITISED() entries here must have corresponding
@@ -4646,12 +4650,10 @@ id_to_sys_reg_desc(struct kvm_vcpu *vcpu, u64 id,
 		return ((struct sys_reg_desc *)r)->val;			\
 	}
 
-FUNCTION_INVARIANT(revidr_el1)
 FUNCTION_INVARIANT(aidr_el1)
 
 /* ->val is filled in by kvm_sys_reg_table_init() */
 static struct sys_reg_desc invariant_sys_regs[] __ro_after_init = {
-	{ SYS_DESC(SYS_REVIDR_EL1), NULL, reset_revidr_el1 },
 	{ SYS_DESC(SYS_AIDR_EL1), NULL, reset_aidr_el1 },
 };
 
@@ -4999,6 +5001,9 @@ static void vcpu_set_hcr(struct kvm_vcpu *vcpu)
 	else
 		vcpu->arch.hcr_el2 |= HCR_TID2;
 
+	if (kvm_read_vm_id_reg(kvm, SYS_REVIDR_EL1) != read_sysreg(REVIDR_EL1))
+		vcpu->arch.hcr_el2 |= HCR_TID1;
+
 	if (vcpu_el1_is_32bit(vcpu))
 		vcpu->arch.hcr_el2 &= ~HCR_RW;
 
-- 
2.42.0