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

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Date:   Mon, 4 Jul 2022 15:18:54 +0800
From:   Dave Young <dyoung@...hat.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        "Eric W. Biederman" <ebiederm@...ssion.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>,
        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,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>, kexec@...ts.infradead.org
Subject: Re: [PATCHv7 11/14] x86: Disable kexec if system has unaccepted memory

On Wed, 29 Jun 2022 at 08:59, Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> On Tue, Jun 28, 2022 at 05:10:56PM -0700, Dave Hansen wrote:
> > On 6/28/22 16:51, Kirill A. Shutemov wrote:
> > > On Fri, Jun 24, 2022 at 05:00:05AM +0300, Kirill A. Shutemov wrote:
> > >>> If there is some deep and fundamental why this can not be supported
> > >>> then it probably makes sense to put some code in the arch_kexec_load
> > >>> hook that verifies that deep and fundamental reason is present.
> > ...
> > > +   /*
> > > +    * TODO: Information on memory acceptance status has to be communicated
> > > +    * between kernel.
> > > +    */
> >
> > So, the deep and fundamental reason is... drum roll... you haven't
> > gotten around to implementing bitmap passing yet?!?!?   I have the
> > feeling that wasn't what Eric was looking for.
>
> The deep fundamental reason is that everything cannot be implemented and
> upstreamed at once.

If the only thing is to pass bitmap to kexec kernel, since you have
reserved the bitmap memory I guess it is straightforward to set the
kexec bootparams.unaccepted_memory as the old value.  Not sure if
there are problems when the decompress code accepts memory again
though.
for kernel kexec_file_load, refer to function setup_boot_parameters()
in arch/x86/kernel/kexec-bzimage64.c for kexec_file_load,
for kexec-tools kexec_load code refer to
setup_linux_system_parameters() kexec/arch/i386/x86-linux-setup.c

Thanks
Dave