Message-ID: <20220719220128.xl7yo4lk6uxwxilf@black.fi.intel.com>
Date:   Wed, 20 Jul 2022 01:01:28 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>, Peter Gonda <pgonda@...gle.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Dionna Amalie Glaze <dionnaglaze@...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, Jul 19, 2022 at 11:50:57PM +0200, Borislav Petkov wrote:
> On Tue, Jul 19, 2022 at 02:35:45PM -0700, Dave Hansen wrote:
> > They're trying to design something that can (forever) handle guests that
> > might not be able to accept memory. 
> 
> Wait, what?
> 
> If you can't modify those guests to teach them to accept memory, how do
> you add TDX or SNP guest support to them?
> 
> I.e., you need to modify the guests and then you can add memory
> acceptance. Basically, your point below...
> 
> > It's based on the idea that *something* needs to assume control and
> > EFI doesn't have enough information to assume control.
> >
> > I wish we didn't need all this complexity, though.
> > 
> > There are three entities that can influence how much memory is accepted:
> > 
> > 1. The host
> > 2. The guest firmware
> > 3. The guest kernel (or bootloader or something after the firmware)
> > 
> > This whole thread is about how #2 and #3 talk to each other and make
> > sure *someone* does it.
> > 
> > I kinda think we should just take the guest firmware out of the picture.
> >  There are only going to be a few versions of the kernel that can boot
> > under TDX (or SEV-SNP) and *can't* handle unaccepted memory.  It seems a
> > bit silly to design this whole interface for a few versions of the OS
> > that TDX folks tell me can't be used anyway.
> > 
> > I think we should just say if you want to run an OS that doesn't have
> > unaccepted memory support, you can either:
> > 
> > 1. Deal with that at the host level configuration
> > 2. Boot some intermediate thing like a bootloader that does acceptance
> >    before running the stupid^Wunenlightended OS
> > 3. Live with the 4GB of pre-accepted memory you get with no OS work.
> > 
> > Yeah, this isn't convenient for some hosts.  But, really, this is
> > preferable to doing an EFI/OS dance until the end of time.
> 
> Ack. Definitely.

I like it too as it is no-code solution :P

Peter, I'm pretty sure unaccepted memory support hits upstream well before
TDX get adopted widely in production. I think it is pretty reasonable to
deal with it on host side in meanwhile.

Any objections?

-- 
 Kirill A. Shutemov

Powered by blists - more mailing lists