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From: Ard Biesheuvel <ardb@kernel.org>
Date: Sat, 2 Mar 2024 00:46:06 +0100
Message-ID: <CAMj1kXHnXRBke1P5nqLwuprJzyKk36bZQPNfwSerAYunvPAzMA@mail.gmail.com>
Subject: Re: [PATCH v7 6/9] x86/boot: Move mem_encrypt= parsing to the decompressor
To: Borislav Petkov <bp@alien8.de>
Cc: Ard Biesheuvel <ardb+git@google.com>, linux-kernel@vger.kernel.org, 
	Kevin Loughlin <kevinloughlin@google.com>, Tom Lendacky <thomas.lendacky@amd.com>, 
	Dionna Glaze <dionnaglaze@google.com>, Thomas Gleixner <tglx@linutronix.de>, 
	Ingo Molnar <mingo@redhat.com>, Dave Hansen <dave.hansen@linux.intel.com>, 
	Andy Lutomirski <luto@kernel.org>, Brian Gerst <brgerst@gmail.com>
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On Fri, 1 Mar 2024 at 20:17, Borislav Petkov <bp@alien8.de> wrote:
>
> On Tue, Feb 27, 2024 at 04:19:14PM +0100, Ard Biesheuvel wrote:
> > diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
> > index 01d19fc22346..eeea058cf602 100644
> > --- a/arch/x86/include/uapi/asm/bootparam.h
> > +++ b/arch/x86/include/uapi/asm/bootparam.h
> > @@ -38,6 +38,7 @@
> >  #define XLF_EFI_KEXEC                        (1<<4)
> >  #define XLF_5LEVEL                   (1<<5)
> >  #define XLF_5LEVEL_ENABLED           (1<<6)
> > +#define XLF_MEM_ENCRYPTION           (1<<7)
>
> Needs documenting in Documentation/arch/x86/boot.rst.
>

Ack.

> And yes, those 5LEVEL things are not documented either but I'm even
> questioning the justification for their existence. We'll see...
>

Yeah that seems unnecessary to me. They are only used by kexec, and
only for cases where you want to kexec a [much] older kernel that
cannot deal with 5-level paging at all. AFAICT 5-level support was
added in v4.13.

So I think we might be able to drop these entirely, no?