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

[Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>]

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