KVM: arm64: nv: Apply RESx settings to sysreg reset values

While we have sanitisation in place for the guest sysregs, we lack
that sanitisation out of reset. So some of the fields could be
evaluated and not reflect their RESx status, which sounds like
a very bad idea.

Apply the RESx masks to the the sysreg file in two situations:

- when going via a reset of the sysregs

- after having computed the RESx masks

Having this separate reset phase from the actual reset handling is
a bit grotty, but we need to apply this after the ID registers are
final.

Tested-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20250112165029.1181056-3-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_nested.h

@@ -186,7 +186,7 @@ static inline bool kvm_supported_tlbi_s1e2_op(struct kvm_vcpu *vpcu, u32 instr)
 	return true;
 }
 
-int kvm_init_nv_sysregs(struct kvm *kvm);
+int kvm_init_nv_sysregs(struct kvm_vcpu *vcpu);
 
 #ifdef CONFIG_ARM64_PTR_AUTH
 bool kvm_auth_eretax(struct kvm_vcpu *vcpu, u64 *elr);

arch/arm64/kvm/nested.c

@@ -963,14 +963,15 @@ static __always_inline void set_sysreg_masks(struct kvm *kvm, int sr, u64 res0,
 	kvm->arch.sysreg_masks->mask[i].res1 = res1;
 }
 
-int kvm_init_nv_sysregs(struct kvm *kvm)
+int kvm_init_nv_sysregs(struct kvm_vcpu *vcpu)
 {
+	struct kvm *kvm = vcpu->kvm;
 	u64 res0, res1;
 
 	lockdep_assert_held(&kvm->arch.config_lock);
 
 	if (kvm->arch.sysreg_masks)
-		return 0;
+		goto out;
 
 	kvm->arch.sysreg_masks = kzalloc(sizeof(*(kvm->arch.sysreg_masks)),
 					 GFP_KERNEL_ACCOUNT);
@@ -1271,6 +1272,10 @@ int kvm_init_nv_sysregs(struct kvm *kvm)
 		res0 |= MDCR_EL2_EnSTEPOP;
 	set_sysreg_masks(kvm, MDCR_EL2, res0, res1);
 
+out:
+	for (enum vcpu_sysreg sr = __SANITISED_REG_START__; sr < NR_SYS_REGS; sr++)
+		(void)__vcpu_sys_reg(vcpu, sr);
+
 	return 0;
 }
 

arch/arm64/kvm/sys_regs.c

@@ -4396,6 +4396,9 @@ void kvm_reset_sys_regs(struct kvm_vcpu *vcpu)
 			reset_vcpu_ftr_id_reg(vcpu, r);
 		else
 			r->reset(vcpu, r);
+
+		if (r->reg >= __SANITISED_REG_START__ && r->reg < NR_SYS_REGS)
+			(void)__vcpu_sys_reg(vcpu, r->reg);
 	}
 
 	set_bit(KVM_ARCH_FLAG_ID_REGS_INITIALIZED, &kvm->arch.flags);
@@ -4999,7 +5002,7 @@ int kvm_finalize_sys_regs(struct kvm_vcpu *vcpu)
 	}
 
 	if (vcpu_has_nv(vcpu)) {
-		int ret = kvm_init_nv_sysregs(kvm);
+		int ret = kvm_init_nv_sysregs(vcpu);
 		if (ret)
 			return ret;
 	}