linux-kernel - Re: [PATCHv7 00/14] mm, x86/cc: Implement support for unaccepted memory

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Message-ID: <CAAH4kHaB2tL+sAn0NAciu5DQeX5hpNkDees=n=f83S=Ph9Y6tw@mail.gmail.com>
Date:   Tue, 19 Jul 2022 11:29:32 -0700
From:   Dionna Amalie Glaze <dionnaglaze@...gle.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>, Peter Gonda <pgonda@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Marcelo Cerri <marcelo.cerri@...onical.com>,
        tim.gardner@...onical.com,
        Khalid ElMously <khalid.elmously@...onical.com>,
        philip.cox@...onical.com,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-coco@...ts.linux.dev, linux-efi <linux-efi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Yao, Jiewen" <jiewen.yao@...el.com>
Subject: Re: [PATCHv7 00/14] mm, x86/cc: Implement support for unaccepted memory

> > > I think we should make it obvious from a kernel image if it supports
> > > unaccepted memory (with UTS_VERSION or other way).
> > >
>
> Something I didn't address in my previous email: how would the UEFI
> know where the kernel is to parse this UTS_VERSION out when it's
> booting a bootloader before Linux gets booted?
>

How about instead of the limited resource of UTS_VERSION, we add a
SETUP_BOOT_FEATURES enum for setup_data in the boot header? That would
be easier to parse out and more extensible in the future.
https://www.kernel.org/doc/html/latest/x86/boot.html?highlight=boot

This can contain a bitmap of a number of features that we currently
need manual tagging for, such as SEV guest support, SEV-SNP guest
support, TDX guest support, and (CONFIG_UNACCEPTED_MEMORY, TDX) or
(CONFIG_UNACCEPTED_MEMORY, SEV-SNP).
The VMM, UEFI, or boot loader can read these from the images/kernels
and have the appropriate behavior.

-- 
-Dionna Glaze, PhD (she/her)