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

[Huang, Kai]

On Mon, 2025-05-26 at 23:10 +0000, Huang, Kai wrote:
> On Mon, 2025-05-26 at 16:45 -0400, 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)));
> > \
> > })
> 
> Just FYI the above warning can also be triggered when CONFIG_SPARSEMEM_VMEMMAP=y
> (and CONFIG_SPARSEMEM=y as well), in which case the __page_to_pfn() is simply:
> 
>   #define __page_to_pfn(page)     (unsigned long)((page) - vmemmap)
> 
> The function call to page_to_section() and __section_mem_map_addr() only happens
> when CONFIG_SPARSEMEM_VMEMMAP=n while CONFIG_SPARSEMEM=y.
> 

[...]


> 
> I did some test and can confirm this patch can silence the warning mentioned in
> the changelog.
> 
> However, with this patch applied, I also tested the case that
> CONFIG_SPARSEMEM_VMEMMAP=n and CONFIG_SPARSEMEM=y [1], but I still got:
> 
> vmlinux.o: warning: objtool: tdh_vp_enter+0x10: call to page_to_section() leaves
> .noinstr.text section
> 
> Not sure why, but it seems __flatten failed to work as expected, as least
> recursively.
> 

I found a recently merged patch from Kirill has made CONFIG_SPARSEMEM_VMEMAP
always true on x86_64:

https://lore.kernel.org/lkml/174748683804.406.11521945321481191771.tip-bot2@tip-bot2/

So we don't need to worry about the case that CONFIG_SPARSEMEM_VMEMMAP=n and
CONFIG_SPARSEMEM=y.

The changelog could be simplified/updated though I think (since seems there's no
need to mention the "large" case now).

So:

Tested-by: Kai Huang <kai.huang@xxxxxxxxx>
Acked-by: Kai Huang <kai.huang@xxxxxxxxx>