Received-SPF: pass (google.com: domain of linux-kernel+bounces-46704-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Date: Wed, 31 Jan 2024 23:23:50 +0800
From: Baoquan He <bhe@redhat.com>
To: "Huang, Kai" <kai.huang@intel.com>,
	Nikolay Borisov <nik.borisov@suse.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Hunter, Adrian" <adrian.hunter@intel.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
	"Reshetova, Elena" <elena.reshetova@intel.com>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"Kalra, Ashish" <ashish.kalra@amd.com>,
	Sean Christopherson <seanjc@google.com>,
	"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	"linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCHv6 00/16] x86/tdx: Add kexec support
Message-ID: <ZbpmBulaR7eft/CE@MiWiFi-R3L-srv>
References: <20240124125557.493675-1-kirill.shutemov@linux.intel.com>
 <3f44458f-2b4a-4464-a3df-cb791298dafc@redhat.com>
 <efe20a00-9a7c-4c03-8fcc-fce265cdbf0e@suse.com>
 <ZbpBbAkPxQZ6gHoE@MiWiFi-R3L-srv>
 <5d91fc11-0b3b-40f0-872d-abdbb4038f76@suse.com>
 <BL1PR11MB5978633DF36A69F8020818E1F77C2@BL1PR11MB5978.namprd11.prod.outlook.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <BL1PR11MB5978633DF36A69F8020818E1F77C2@BL1PR11MB5978.namprd11.prod.outlook.com>

On 01/31/24 at 01:07pm, Huang, Kai wrote:
> > > Runtime disabling kexec looks better than at cmpile time, esp for
> > > distros. While from above patch, making using of kexec_load_disabled
> > > to achive the runtime disabling may not be so good. Because we have a
> > > front door to enable it through:
> > >
> > > /proc/sys/kernel/kexec_load_disabled
> > 
> > AFAIU it can't be enabled via this sysctl because the handler for it expects
> > only 1 to be written to it:
> > 
> >       2                 .proc_handler   = proc_dointvec_minmax,
> > 
> >       1                 .extra1         = SYSCTL_ONE,
> > 
> >    994                  .extra2         = SYSCTL_ONE,
> > 
> 
> This is also my understanding.  
> 
> The documentation also says once it is turned to disable we cannot turn back again:
> 
> kexec_load_disable
> ===================
> 
> A toggle indicating if the syscalls ``kexec_load`` and
> ``kexec_file_load`` have been disabled.
> This value defaults to 0 (false: ``kexec_*load`` enabled), but can be
> set to 1 (true: ``kexec_*load`` disabled).
> Once true, kexec can no longer be used, and the toggle cannot be set
> back to false.

you are quite right, I have never noticed this, thanks.

Then then mentioned patch looks good to me.