[PATCH v6 27/64] KVM: arm64: nv: Allow a sysreg to be hidden from userspace only

[Marc Zyngier]

So far, we never needed to distinguish between registers hidden
from userspace and being hidden from a guest (they are always
either visible to both, or hidden from both).

With NV, we have the ugly case of the EL{0,1}2 registers, which
are only a view on the EL{0,1} registers. It makes absolutely no
sense to expose them to userspace, since it already has the
canonical view.

Add a new visibility flag (REG_HIDDEN_USER) and a new helper that
checks for it and REG_HIDDEN when checking whether to expose
a sysreg to userspace. Subsequent patches will make use of it.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/sys_regs.c |  6 +++---
 arch/arm64/kvm/sys_regs.h | 12 +++++++++++-
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 31d739d59f67..0c9bbe5eee5e 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -3031,7 +3031,7 @@ int kvm_arm_sys_reg_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
 		return get_invariant_sys_reg(reg->id, uaddr);
 
 	/* Check for regs disabled by runtime config */
-	if (sysreg_hidden(vcpu, r))
+	if (sysreg_hidden_user(vcpu, r))
 		return -ENOENT;
 
 	if (r->get_user)
@@ -3056,7 +3056,7 @@ int kvm_arm_sys_reg_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
 		return set_invariant_sys_reg(reg->id, uaddr);
 
 	/* Check for regs disabled by runtime config */
-	if (sysreg_hidden(vcpu, r))
+	if (sysreg_hidden_user(vcpu, r))
 		return -ENOENT;
 
 	if (r->set_user)
@@ -3127,7 +3127,7 @@ static int walk_one_sys_reg(const struct kvm_vcpu *vcpu,
 	if (!(rd->reg || rd->get_user))
 		return 0;
 
-	if (sysreg_hidden(vcpu, rd))
+	if (sysreg_hidden_user(vcpu, rd))
 		return 0;
 
 	if (!copy_reg_to_user(rd, uind))
diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
index cc0cc95a0280..850629f083a3 100644
--- a/arch/arm64/kvm/sys_regs.h
+++ b/arch/arm64/kvm/sys_regs.h
@@ -78,7 +78,8 @@ struct sys_reg_desc {
 };
 
 #define REG_HIDDEN		(1 << 0) /* hidden from userspace and guest */
-#define REG_RAZ			(1 << 1) /* RAZ from userspace and guest */
+#define REG_HIDDEN_USER		(1 << 1) /* hidden from userspace only */
+#define REG_RAZ			(1 << 2) /* RAZ from userspace and guest */
 
 static __printf(2, 3)
 inline void print_sys_reg_msg(const struct sys_reg_params *p,
@@ -138,6 +139,15 @@ static inline bool sysreg_hidden(const struct kvm_vcpu *vcpu,
 	return r->visibility(vcpu, r) & REG_HIDDEN;
 }
 
+static inline bool sysreg_hidden_user(const struct kvm_vcpu *vcpu,
+				      const struct sys_reg_desc *r)
+{
+	if (likely(!r->visibility))
+		return false;
+
+	return r->visibility(vcpu, r) & (REG_HIDDEN | REG_HIDDEN_USER);
+}
+
 static inline bool sysreg_visible_as_raz(const struct kvm_vcpu *vcpu,
 					 const struct sys_reg_desc *r)
 {
-- 
2.30.2