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

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Date:   Tue, 9 Aug 2022 13:36:00 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...el.com>, Marc Orr <marcorr@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Dionna Amalie Glaze <dionnaglaze@...gle.com>,
        Peter Gonda <pgonda@...gle.com>,
        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>,
        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

On Tue, 9 Aug 2022 at 13:11, Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> On Sat, Jul 23, 2022 at 01:14:07PM +0200, Ard Biesheuvel wrote:
> > On Thu, 21 Jul 2022 at 19:13, Dave Hansen <dave.hansen@...el.com> wrote:
> > >
> > > On 7/19/22 17:26, Marc Orr wrote:
> > > > - Dave's suggestion to "2. Boot some intermediate thing like a
> > > > bootloader that does acceptance ..." is pretty clever! So if upstream
> > > > thinks this FW-kernel negotiation is not a good direction, maybe we
> > > > (Google) can pursue this idea to avoid introducing yet another tag on
> > > > our images.
> > >
> > > I'm obviously speaking only for myself here and not for "upstream" as a
> > > whole, but I clearly don't like the FW/kernel negotiation thing.  It's a
> > > permanent pain in our necks to solve a very temporary problem.
> >
> > EFI is basically our existing embodiment of this fw/kernel negotiation
> > thing, and iff we need it, I have no objection to using it for this
> > purpose, i.e., to allow the firmware to infer whether or not it should
> > accept all available memory on behalf of the OS before exiting boot
> > services. But if we don't need this, even better.
>
> FW/kernel negotiation does not work if there's a boot loader in the middle
> that does ExitBootServices(). By the time kernel can announce if it
> supports unaccepted memory there's nobody to announce to.
>

Why would you want to support such bootloaders for TDX anyway? TDX
heavily relies on measured boot abstractions and other things that are
heavily tied to firmware.