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

Marc Zyngier
2022-01-28T12:20:15Z

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@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)
{