Re: [PATCH] x86/efistub: Don't try to print after ExitBootService()

[Nikolay Borisov]

On 12.10.23 г. 13:14 ч., kirill.shutemov@xxxxxxxxxxxxxxx wrote:
> On Wed, Oct 11, 2023 at 10:25:28PM +0300, Nikolay Borisov wrote:
> > setup_e820() is executed after UEFI's ExitBootService has been called.
> > This causes the firmware to throw an exception because Console IO
> > protocol handler is supposed to work only during boot service
> > environment. As per UEFI 2.9, section 12.1:
> >
> >   "This protocol isused to handle input and output of text-based
> >   information intended for the system user during the operation of code
> >   in the boot services environment."
> >
> > Running a TDX guest with TDVF with unaccepted memory disabled results in
> > the following output:
>
> Oh. My bad.
>
> But there's other codepath that does the same. If setup_e820() fails with
> EFI_BUFFER_TOO_SMALL, efi_stub_entry() would try to print "exit_boot()
> failed\n".
>
> I wouldner if it is feasible to hook up earlyprintk console into
> efi_printk() machinery for after ExitBootService() case? Silent boot
> failure is not the best UX.


In my testing I was able to transpose setup_e820 and efi 
exit_boot_service by calling exit_boot_func before setup_e820 which 
ensures the various memory variables are populated. Is there any 
specific reason why ExitBootServices is called before setting up the 
e820 table? AFAIU this is an arbitrary choice?