KVM: arm64: Reintroduce __sve_save_state

Now that the hypervisor is handling the host sve state in
protected mode, it needs to be able to save it.

This reverts commit e66425fc ("KVM: arm64: Remove unused
__sve_save_state").
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20240603122852.3923848-2-tabba@google.comSigned-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_hyp.h

@@ -111,6 +111,7 @@ void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu);
 
 void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
 void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
+void __sve_save_state(void *sve_pffr, u32 *fpsr);
 void __sve_restore_state(void *sve_pffr, u32 *fpsr);
 
 u64 __guest_enter(struct kvm_vcpu *vcpu);

arch/arm64/kvm/hyp/fpsimd.S

@@ -25,3 +25,9 @@ SYM_FUNC_START(__sve_restore_state)
 	sve_load 0, x1, x2, 3
 	ret
 SYM_FUNC_END(__sve_restore_state)
+
+SYM_FUNC_START(__sve_save_state)
+	mov	x2, #1
+	sve_save 0, x1, x2, 3
+	ret
+SYM_FUNC_END(__sve_save_state)