linux-kernel - Re: [PATCH, RESEND] x86/pat: Simplifying the PAT programming protocol

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Date: Tue, 13 Feb 2024 17:15:14 +0100
From: Borislav Petkov <bp@...en8.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Isaku Yamahata <isaku.yamahata@...el.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH, RESEND] x86/pat: Simplifying the PAT programming protocol

On Thu, Feb 01, 2024 at 12:17:32AM +0200, Kirill A. Shutemov wrote:
> > So the "relaxation" is the removal of that CR0.CD requirement?

So I'm looking at the SDM, revisions 081US and 082US.

Section

"12.11.8 MTRR Considerations in MP Systems"

still has

"4. Enter the no-fill cache mode. (Set the CD flag in control register
CR0 to 1 and the NW flag to 0.)"

and

"4. Enter the no-fill cache mode. (Set the CD flag in control register
CR0 to 1 and the NW flag to 0.)"

so where is that relaxation written? Am I looking at the wrong place?

> And double WBINVD if the machine has no X86_FEATURE_SELFSNOOP (before and
> after TLB flush).

That's still there too. Steps 5 and 11, respectively.

Hmmm?

-- 
Regards/Gruss,
    Boris.

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