linux-kernel - Re: [PATCH v7 6/9] x86/boot: Move mem_encrypt= parsing to the decompressor

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Date: Sat, 2 Mar 2024 00:46:06 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, 
	Kevin Loughlin <kevinloughlin@...gle.com>, Tom Lendacky <thomas.lendacky@....com>, 
	Dionna Glaze <dionnaglaze@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Andy Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v7 6/9] x86/boot: Move mem_encrypt= parsing to the decompressor

On Fri, 1 Mar 2024 at 20:17, Borislav Petkov <bp@...en8.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?