x86/tdx: mark tdh_vp_enter() as __flatten

In some cases tdx_tdvpr_pa() is not fully inlined into tdh_vp_enter(), which
causes the following warning:

  vmlinux.o: warning: objtool: tdh_vp_enter+0x8: call to tdx_tdvpr_pa() leaves .noinstr.text section

This happens if the compiler considers tdx_tdvpr_pa() to be "large", for example
because CONFIG_SPARSEMEM adds two function calls to page_to_section() and
__section_mem_map_addr():

({      const struct page *__pg = (pg);                         \
        int __sec = page_to_section(__pg);                      \
        (unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec)));
\
})

Because exiting the noinstr section is a no-no, just mark tdh_vp_enter() for
full inlining.

Reported-by: kernel test robot <[email protected]>
Analyzed-by: Xiaoyao Li <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Paolo Bonzini <[email protected]>

Author: bonzini

arch/x86/virt/vmx/tdx/tdx.c

@@ -1517,7 +1517,7 @@ static void tdx_clflush_page(struct page *page)
 	clflush_cache_range(page_to_virt(page), PAGE_SIZE);
 }
 
-noinstr u64 tdh_vp_enter(struct tdx_vp *td, struct tdx_module_args *args)
+noinstr __flatten u64 tdh_vp_enter(struct tdx_vp *td, struct tdx_module_args *args)
 {
 	args->rcx = tdx_tdvpr_pa(td);