linux-kernel - Re: [PATCH] x86/fred: Fix 64bit identifier in fred

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Message-ID: <20dd9552-65fd-4887-a6f9-667a8d7eed34@zytor.com>
Date: Fri, 15 Aug 2025 09:21:23 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Andrew Cooper <andrew.cooper3@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc: Xin Li <xin@...or.com>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Subject: Re: [PATCH] x86/fred: Fix 64bit identifier in fred_ss

On 2025-08-14 12:04, Andrew Cooper wrote:
> FRED can only be enabled in Long Mode.  This is the 64bit mode (as opposed to
> compatibility mode) identifier, rather than being something hard-wired at 1.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@...rix.com>

[...]


> IIRC, this was wrong in an older version of the FRED spec.  I made the same
> mistake in Xen, and I didn't copy Linux's structure.
> 
> I don't thinks this warrants backporting, but the fixes tag is:
> 
> Fixes: 3c77bf02d0c0 ("x86/ptrace: Add FRED additional information to the pt_regs structure")

Please make it explicit that this patch is "no functional change", i.e.
it is naming-only patch.

Other than that:

Reviewed-by: H. Peter Anvin (Intel) <hpa@...or.com>