linux-kernel - Re: [PATCHv2 3/7] efi/x86: Implement support for unaccepted memory

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Date:   Wed, 12 Jan 2022 11:35:23 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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>,
        Ard Biesheuvel <ardb@...nel.org>,
        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>, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 3/7] efi/x86: Implement support for unaccepted memory

On 1/12/22 11:29 AM, Kirill A. Shutemov wrote:
>>> +	 * In the worst case scenario -- a huge hole in the middle of the
>>> +	 * address space -- It needs 256MiB to handle 4PiB of the address
>>> +	 * space.
>>> +	 *
>>> +	 * TODO: handle situation if params->unaccepted_memory has already set.
>>> +	 * It's required to deal with kexec.
>> What happens today with kexec() since its not dealt with?
> I didn't give it a try, but I assume it will hang.
> 
> There are more things to do to make kexec working and safe. We will get
> there, but it is not top priority.

Well, if we know it's broken, shouldn't we at least turn kexec off?

It would be dirt simple to do in Kconfig.  As would setting:

	kexec_load_disabled = true;

which would probably also do the trick.  That's from three seconds of
looking.  I'm sure you can come up with something better.