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

From: Dave Young <dyoung@redhat.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	 Borislav Petkov <bp@alien8.de>,
	Andy Lutomirski <luto@kernel.org>,
	Sean Christopherson <seanjc@google.com>,
	 Andrew Morton <akpm@linux-foundation.org>,
	Joerg Roedel <jroedel@suse.de>,  Ard Biesheuvel <ardb@kernel.org>,
	Andi Kleen <ak@linux.intel.com>,
	 Kuppuswamy Sathyanarayanan
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	 David Rientjes <rientjes@google.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	 Tom Lendacky <thomas.lendacky@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	 Peter Zijlstra <peterz@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	 Ingo Molnar <mingo@redhat.com>,
	Varad Gautam <varad.gautam@suse.com>,
	 Dario Faggioli <dfaggioli@suse.com>,
	Mike Rapoport <rppt@kernel.org>,
	 David Hildenbrand <david@redhat.com>,
	marcelo.cerri@canonical.com, tim.gardner@canonical.com,
	 khalid.elmously@canonical.com, philip.cox@canonical.com,
	 "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>,
	linux-mm@kvack.org, linux-coco@lists.linux.dev,
	 linux-efi@vger.kernel.org,
	 "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<linux-kernel@vger.kernel.org>,
	kexec@lists.infradead.org
Subject: Re: [PATCHv7 11/14] x86: Disable kexec if system has unaccepted memory
Date: Mon, 4 Jul 2022 15:18:54 +0800	[thread overview]
Message-ID: <CALu+AoQdEGpecj1wm9U2MpKqPbN5UmFF6+w3JaJSvddeRwf0dw@mail.gmail.com> (raw)
In-Reply-To: <20220629005915.gieli3dbjzvjbk5i@black.fi.intel.com>

On Wed, 29 Jun 2022 at 08:59, Kirill A. Shutemov
<kirill.shutemov@linux.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