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

[kirill . shutemov]

On Thu, Oct 12, 2023 at 01:51:13PM +0300, Nikolay Borisov wrote:
> 
> 
> 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?

Because if you allocate memory with EFI service it can alter EFI memory
map and we need the last version to convert it to e820.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov