KVM: arm64: Extend unified RESx handling to runtime sanitisation

Add a new helper to retrieve the RESx values for a given system
register, and use it for the runtime sanitisation.

This results in slightly better code generation for a fairly hot
path in the hypervisor, and additionally covers all sanitised
registers in all conditions, not just the VNCR-based ones.

Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-6-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Marc Zyngier

arch/arm64/include/asm/kvm_host.h

@@ -635,6 +635,21 @@ struct kvm_sysreg_masks {
 	struct resx mask[NR_SYS_REGS - __SANITISED_REG_START__];
 };
 
+static inline struct resx __kvm_get_sysreg_resx(struct kvm_arch *arch,
+						enum vcpu_sysreg sr)
+{
+	struct kvm_sysreg_masks *masks;
+
+	masks = arch->sysreg_masks;
+	if (likely(masks &&
+		   sr >= __SANITISED_REG_START__ && sr < NR_SYS_REGS))
+		return masks->mask[sr - __SANITISED_REG_START__];
+
+	return (struct resx){};
+}
+
+#define kvm_get_sysreg_resx(k, sr) __kvm_get_sysreg_resx(&(k)->arch, (sr))
+
 static inline void __kvm_set_sysreg_resx(struct kvm_arch *arch,
 					 enum vcpu_sysreg sr, struct resx resx)
 {

arch/arm64/kvm/emulate-nested.c

@@ -2427,15 +2427,7 @@ static enum trap_behaviour compute_trap_behaviour(struct kvm_vcpu *vcpu,
 
 static u64 kvm_get_sysreg_res0(struct kvm *kvm, enum vcpu_sysreg sr)
 {
-	struct kvm_sysreg_masks *masks;
-
-	/* Only handle the VNCR-backed regs for now */
-	if (sr < __VNCR_START__)
-		return 0;
-
-	masks = kvm->arch.sysreg_masks;
-
-	return masks->mask[sr - __SANITISED_REG_START__].res0;
+	return kvm_get_sysreg_resx(kvm, sr).res0;
 }
 
 static bool check_fgt_bit(struct kvm_vcpu *vcpu, enum vcpu_sysreg sr,

arch/arm64/kvm/nested.c

@@ -1669,16 +1669,11 @@ u64 limit_nv_id_reg(struct kvm *kvm, u32 reg, u64 val)
 u64 kvm_vcpu_apply_reg_masks(const struct kvm_vcpu *vcpu,
 			     enum vcpu_sysreg sr, u64 v)
 {
-	struct kvm_sysreg_masks *masks;
-
-	masks = vcpu->kvm->arch.sysreg_masks;
-
-	if (masks) {
-		sr -= __SANITISED_REG_START__;
+	struct resx resx;
 
-		v &= ~masks->mask[sr].res0;
-		v |= masks->mask[sr].res1;
-	}
+	resx = kvm_get_sysreg_resx(vcpu->kvm, sr);
+	v &= ~resx.res0;
+	v |= resx.res1;
 
 	return v;
 }