Re: [PATCH] x86/tdx: mark tdh_vp_enter() as __flatten

[Sean Christopherson <seanjc@google.com>]

On Mon, May 26, 2025, Paolo Bonzini wrote:
> 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 <lkp@intel.com>
> Analyzed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202505240530.5KktQ5mX-lkp@intel.com/
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/virt/vmx/tdx/tdx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index f5e2a937c1e7..2457d13c3f9e 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/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);

The "standard" kernel way of handling this it to mark the offending helper
__always_inline, i.e. tag tdx_tdvpr_pa() __always_inline.  Ditto for tdx_tdr_pa().
Especially since they're already "inline".