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

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Message-ID: <20240430125744.GQZjDqyM3k_peEw-bc@fat_crate.local>
Date: Tue, 30 Apr 2024 14:57:44 +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 06:16:54PM +0300, Kirill A. Shutemov wrote:
> Yes, that's what happens in current upstream.

Let's rewrite that commit message then:

"TDX guests run with MCA enabled (CR4.MCE=1b) from the very start. If
that bit is cleared during CR4 register reprogramming during boot or
kexec flows, a #VE exception will be raised which the guest kernel
cannot handle that early.

Therefore, make sure the CR4.MCE setting is preserved over kexec too and
avoid raising any #VEs."

without that bit about TDX guests might be allowed to clear CR4.MCE
which is only confusing and unnecessary.

Thx.

-- 
Regards/Gruss,
    Boris.

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