KVM: arm64: Add a visibility bit to ignore user writes

We're about to ignore writes to AArch32 ID registers on AArch64-only
systems. Add a bit to indicate a register is handled as write ignore
when accessed from userspace.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220913094441.3957645-6-oliver.upton@linux.dev

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 0e20a31..6d05112 100644 (file)
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2775,6 +2775,9 @@ int kvm_sys_reg_set_user(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg,
        if (!r)
                return -ENOENT;
 
+       if (sysreg_user_write_ignore(vcpu, r))
+               return 0;
+
        if (r->set_user) {
                ret = (r->set_user)(vcpu, r, val);
        } else {

diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
index e78b510..e4ebb3a 100644 (file)
--- a/arch/arm64/kvm/sys_regs.h
+++ b/arch/arm64/kvm/sys_regs.h
@@ -86,6 +86,7 @@ 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_USER_WI            (1 << 2) /* WI from userspace only */
 
 static __printf(2, 3)
 inline void print_sys_reg_msg(const struct sys_reg_params *p,
@@ -157,6 +158,12 @@ static inline bool sysreg_visible_as_raz(const struct kvm_vcpu *vcpu,
        return sysreg_visibility(vcpu, r) & REG_RAZ;
 }
 
+static inline bool sysreg_user_write_ignore(const struct kvm_vcpu *vcpu,
+                                           const struct sys_reg_desc *r)
+{
+       return sysreg_visibility(vcpu, r) & REG_USER_WI;
+}
+
 static inline int cmp_sys_reg(const struct sys_reg_desc *i1,
                              const struct sys_reg_desc *i2)
 {