linux-kernel - Re: [PATCHv10 05/18] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

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Message-ID: <20240429144454.GHZi-yZkD0boKk5N17@fat_crate.local>
Date: Mon, 29 Apr 2024 16:45:08 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Elena Reshetova <elena.reshetova@...el.com>,
	Jun Nakajima <jun.nakajima@...el.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Ashish Kalra <ashish.kalra@....com>,
	Kai Huang <kai.huang@...el.com>, Baoquan He <bhe@...hat.com>,
	kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv10 05/18] x86/kexec: Keep CR4.MCE set during kexec for
 TDX guest

On Mon, Apr 29, 2024 at 04:17:38PM +0300, Kirill A. Shutemov wrote:
> As I mentioned above, clearing CR4.MCE triggers #VE. It is quirk of the
> platform.

You mean when identity_mapped() runs as part of a kexec-ed kernel, it
might clear CR4.MCE and that would trigger the #VE?

So, if that is correct, you basically want to *preserve* the CR4.MCE
setting across kexec?

But then __mcheck_cpu_init_generic() will go and set it
unconditionally.

So what exactly is the correct flow here?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette