[PATCH v2 08/15] KVM: arm64: nv: Use guest hypervisor's max VL when running nested guest

[Oliver Upton <oliver.upton@linux.dev>]

The max VL for nested guests is additionally constrained by the max VL
selected by the guest hypervisor. Use that instead of KVM's max VL when
running a nested guest.

Note that the guest hypervisor's ZCR_EL2 is sanitised against the VM's
max VL at the time of access, so there's no additional handling required
at the time of use.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/include/hyp/switch.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index 71a93e336a0c..0a6935a18490 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -314,10 +314,22 @@ static bool kvm_hyp_handle_mops(struct kvm_vcpu *vcpu, u64 *exit_code)
 
 static inline void __hyp_sve_restore_guest(struct kvm_vcpu *vcpu)
 {
+	/*
+	 * The vCPU's saved SVE state layout always matches the max VL of the
+	 * vCPU. Start off with the max VL so we can load the SVE state.
+	 */
 	sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1, SYS_ZCR_EL2);
 	__sve_restore_state(vcpu_sve_pffr(vcpu),
 			    &vcpu->arch.ctxt.fp_regs.fpsr);
 
+	/*
+	 * The effective VL for a VM could differ from the max VL when running a
+	 * nested guest, as the guest hypervisor could select a smaller VL. Slap
+	 * that into hardware before wrapping up.
+	 */
+	if (vcpu_has_nv(vcpu) && !is_hyp_ctxt(vcpu))
+		sve_cond_update_zcr_vq(__vcpu_sys_reg(vcpu, ZCR_EL2), SYS_ZCR_EL2);
+
 	write_sysreg_el1(vcpu_sve_zcr_el1(vcpu), SYS_ZCR);
 }
 
-- 
2.45.2.627.g7a2c4fd464-goog