linux-kernel - Re: [PATCHv7 11/14] x86: Disable kexec if system has unaccepted memory

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Date:   Thu, 23 Jun 2022 10:23:59 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "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>
Cc:     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@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        x86@...nel.org, linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org
Subject: Re: [PATCHv7 11/14] x86: Disable kexec if system has unaccepted
 memory

... adding kexec folks

On 6/14/22 05:02, Kirill A. Shutemov wrote:
> On kexec, the target kernel has to know what memory has been accepted.
> Information in EFI map is out of date and cannot be used.
> 
> boot_params.unaccepted_memory can be used to pass the bitmap between two
> kernels on kexec, but the use-case is not yet implemented.
> 
> Disable kexec on machines with unaccepted memory for now.
...
> +static int __init unaccepted_init(void)
> +{
> +	if (!boot_params.unaccepted_memory)
> +		return 0;
> +
> +#ifdef CONFIG_KEXEC_CORE
> +	/*
> +	 * TODO: Information on memory acceptance status has to be communicated
> +	 * between kernel.
> +	 */
> +	pr_warn("Disable kexec: not yet supported on systems with unaccepted memory\n");
> +	kexec_load_disabled = 1;
> +#endif

This looks to be the *only* in-kernel user tweaking kexec_load_disabled.
 It doesn't feel great to just be disabling kexec like this.  Why not
just fix it properly?

What do the kexec folks think?