KVM: arm64: nv: Don't treat ZCR_EL2 as a 'mapped' register

Unlike the other mapped EL2 sysregs ZCR_EL2 isn't guaranteed to be
resident when a vCPU is loaded as it actually follows the SVE
context. As such, the contents of ZCR_EL1 may belong to another guest if
the vCPU has been preempted before reaching sysreg emulation.

Unconditionally use the in-memory value of ZCR_EL2 and switch to the
memory-only accessors. The in-memory value is guaranteed to be valid as
fpsimd_lazy_switch_to_{guest,host}() will restore/save the register
appropriately.

Signed-off-by: Oliver Upton <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>

Author: oupton

arch/arm64/kvm/sys_regs.c

@@ -203,7 +203,6 @@ static void locate_register(const struct kvm_vcpu *vcpu, enum vcpu_sysreg reg,
 		MAPPED_EL2_SYSREG(AMAIR_EL2,   AMAIR_EL1,   NULL	     );
 		MAPPED_EL2_SYSREG(ELR_EL2,     ELR_EL1,	    NULL	     );
 		MAPPED_EL2_SYSREG(SPSR_EL2,    SPSR_EL1,    NULL	     );
-		MAPPED_EL2_SYSREG(ZCR_EL2,     ZCR_EL1,     NULL	     );
 		MAPPED_EL2_SYSREG(CONTEXTIDR_EL2, CONTEXTIDR_EL1, NULL	     );
 		MAPPED_EL2_SYSREG(SCTLR2_EL2,  SCTLR2_EL1,  NULL	     );
 	case CNTHCTL_EL2:
@@ -2709,14 +2708,13 @@ static bool access_zcr_el2(struct kvm_vcpu *vcpu,
 	}
 
 	if (!p->is_write) {
-		p->regval = vcpu_read_sys_reg(vcpu, ZCR_EL2);
+		p->regval = __vcpu_sys_reg(vcpu, ZCR_EL2);
 		return true;
 	}
 
 	vq = SYS_FIELD_GET(ZCR_ELx, LEN, p->regval) + 1;
 	vq = min(vq, vcpu_sve_max_vq(vcpu));
-	vcpu_write_sys_reg(vcpu, vq - 1, ZCR_EL2);
-
+	__vcpu_assign_sys_reg(vcpu, ZCR_EL2, vq - 1);
 	return true;
 }