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.

So looking at the code the only thing which would prevent refactoring to 
exit logic to directly call exit_boot_func etc and setup_e820 before 
calling efi_exit_boot_services is if the memory map changes. The current 
code ensures that we really have the latest memory map version and so 
setup_e820 is called with the latest version.

Ard, how likely it is that the memory map can indeed change between the 
calls to getmemorymap and exitbootservice?