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

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Date:   Thu, 12 Oct 2023 13:14:56 +0300
From:   kirill.shutemov@...ux.intel.com
To:     Nikolay Borisov <nik.borisov@...e.com>
Cc:     ardb@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/efistub: Don't try to print after ExitBootService()

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.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov