Date:   Tue, 19 Jul 2022 02:48:54 +0000
From:   "Yao, Jiewen" <jiewen.yao@...el.com>
To:     Dionna Amalie Glaze <dionnaglaze@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:     Ard Biesheuvel <ardb@...nel.org>, Peter Gonda <pgonda@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Rodel, Jorg" <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>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Mike Rapoport" <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        "Marcelo Cerri" <marcelo.cerri@...onical.com>,
        "tim.gardner@...onical.com" <tim.gardner@...onical.com>,
        Khalid ElMously <khalid.elmously@...onical.com>,
        "Cox, Philip" <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-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

Hey
I posted my comment on Bugzilla https://bugzilla.tianocore.org/show_bug.cgi?id=3987

Let's achieve EDKII/UEFI related discussion there.

Thank you
Yao, Jiewen

> -----Original Message-----
> From: Dionna Amalie Glaze <dionnaglaze@...gle.com>
> Sent: Tuesday, July 19, 2022 7:32 AM
> 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>; Lutomirski, Andy <luto@...nel.org>;
> Christopherson,, Sean <seanjc@...gle.com>; Andrew Morton <akpm@...ux-
> foundation.org>; Rodel, Jorg <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>; Hansen, Dave <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>; Cox, Philip
> <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've talked with our firmware expert today and I think we have a problem
> > with the approach when kernel declaries support of unaccepted memory.
> >
> 
> Is this Jiewen Yao? I've been trying to design the UEFI spec change
> with him. The bootloader problem he commented with this morning was
> something I wasn't fully considering.
> 
> > This apporach doesn't work if we include bootloader into the picture: if
> > EBS() called by bootloader we still cannot know if target kernel supports
> > unaccepted memory and we return to the square 1.
> >
> > I think we should make it obvious from a kernel image if it supports
> > unaccepted memory (with UTS_VERSION or other way).
> >
> > Any comments?
> 
> Is this binary parsing trick already used in EDK2? If not, I wouldn't
> want to introduce an ABI-solidifying requirement like that.
> 
> A bit more cumbersome, but more flexible way to enable the feature is
> an idea I had in a meeting today:
> Make unaccepted memory support a feature-enabling EFI driver installed
> to the EFI system partition.
> 
> * The first time you boot (setup mode), you install an EFI driver that
> just sets a feature Pcd to true (using a custom protocol as Ard had
> suggested above).
> * The second time you boot, if the feature Pcd is true, then the UEFI
> is free to not accept memory and use the unaccepted memory type. The
> bootloader will run after unaccepted memory has been allowed already,
> so there is no accept-all event.
> 
> The default behavior will be to accept all memory when GetMemoryMap is
> called unless the feature pcd is set to true.
> 
> We can then say this driver isn't needed once some new generation of
> this technology comes along and we can require unaccepted memory
> support as part of that technology's baseline, or we manage to update
> the UEFI spec to have GetMemoryMapEx which has unaccepted memory
> support baked in and the bootloaders all know to use it.
> 
> The cloud experience will be, "is boot slow? Install this EFI driver
> from the cloud service provider" to tell the UEFI to enable unaccepted
> memory.
> 
> --
> -Dionna Glaze, PhD (she/her)

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