Build warnings in Xen 5.15.y and 5.10.y with retbleed backports

[Greg KH <gregkh@linuxfoundation.org>]

Hi all,

I'm seeing the following build warning:
	arch/x86/kernel/head_64.o: warning: objtool: xen_hypercall_mmu_update(): can't find starting instruction
in the 5.15.y and 5.10.y retbleed backports.

I don't know why just this one hypercall is being called out by objtool,
and this warning isn't in 5.18 and Linus's tree due to I think commit
5b2fc51576ef ("x86/ibt,xen: Sprinkle the ENDBR") being there.

But, is this a ret call that we "forgot" here?  It's a "real" ret in
Linus's branch:

.pushsection .noinstr.text, "ax"
	.balign PAGE_SIZE
SYM_CODE_START(hypercall_page)
	.rept (PAGE_SIZE / 32)
		UNWIND_HINT_FUNC
		ANNOTATE_NOENDBR
		ANNOTATE_UNRET_SAFE
		ret
		/*
		 * Xen will write the hypercall page, and sort out ENDBR.
		 */
		.skip 31, 0xcc
	.endr

while 5.15.y and older has:
.pushsection .text
	.balign PAGE_SIZE
SYM_CODE_START(hypercall_page)
	.rept (PAGE_SIZE / 32)
		UNWIND_HINT_FUNC
		.skip 31, 0x90
		ANNOTATE_UNRET_SAFE
		RET
	.endr

So should the "ret" remain or be turned into "RET" in mainline right
now?

thanks,

greg k-h