Re: [PATCHv6 00/16] x86/tdx: Add kexec support

From: Baoquan He <bhe@redhat.com>
To: 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, "Rafael J. Wysocki" <rafael@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Kuppuswamy Sathyanarayanan
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	Elena Reshetova <elena.reshetova@intel.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"Kalra, Ashish" <ashish.kalra@amd.com>,
	Sean Christopherson <seanjc@google.com>,
	"Huang, Kai" <kai.huang@intel.com>,
	kexec@lists.infradead.org, linux-coco@lists.linux.dev,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCHv6 00/16] x86/tdx: Add kexec support
Date: Wed, 31 Jan 2024 20:47:40 +0800	[thread overview]
Message-ID: <ZbpBbAkPxQZ6gHoE@MiWiFi-R3L-srv> (raw)
In-Reply-To: <efe20a00-9a7c-4c03-8fcc-fce265cdbf0e@suse.com>

On 01/31/24 at 09:31am, Nikolay Borisov wrote:
> 
> 
> On 30.01.24 г. 15:43 ч., Paolo Bonzini wrote:
> > On 1/24/24 13:55, Kirill A. Shutemov wrote:
> > > The patchset adds bits and pieces to get kexec (and crashkernel) work on
> > > TDX guest.
> > > 
> > > The last patch implements CPU offlining according to the approved ACPI
> > > spec change poposal[1]. It unlocks kexec with all CPUs visible in
> > > the target
> > > kernel. It requires BIOS-side enabling. If it missing we fallback to
> > > booting
> > > 2nd kernel with single CPU.
> > > 
> > > Please review. I would be glad for any feedback.
> > 
> > Hi Kirill,
> > 
> > I have a very basic question: is there a reason why this series does not
> > revert commit cb8eb06d50fc, "x86/virt/tdx: Disable TDX host support when
> > kexec is enabled"?
> 
> While on the topic, Paolo do you think it's  better to have a runtime
> disable of kexec rather than at compile time:
> 
> [RFC PATCH] x86/virt/tdx: Disable KEXEC in the presence of TDX
> 
> 20240118160118.1899299-1-nik.borisov@suse.com

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

If there's a flag or status to check if TDX host is enabled, and does
the checking in kexec_load_permitted(), that could be better. Anyway, I
saw Huang, Kai has posted the tdx host support patchset.

> 
> I'm trying to get traction for this patch.
> 
> 
> > 
> > Thanks,
> > 
> > Paolo
> > 
> > 
> 

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