linux-kernel - Re: [PATCH v3 1/1] x86/fred: Remove ENDBR64 from FRED entry points

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Message-ID: <e5a7d108-f900-4a63-8116-c9eb54171976@intel.com>
Date: Wed, 13 Aug 2025 14:07:00 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Xin Li (Intel)" <xin@...or.com>, linux-kernel@...r.kernel.org
Cc: luto@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, jmill@....edu,
 peterz@...radead.org, andrew.cooper3@...rix.com, stable@...r.kernel.org
Subject: Re: [PATCH v3 1/1] x86/fred: Remove ENDBR64 from FRED entry points

On 7/15/25 23:33, Xin Li (Intel) wrote:
> The FRED specification has been changed in v9.0 to state that there
> is no need for FRED event handlers to begin with ENDBR64, because
> in the presence of supervisor indirect branch tracking, FRED event
> delivery does not enter the WAIT_FOR_ENDBRANCH state.
> 
> As a result, remove ENDBR64 from FRED entry points.

So, the spec is being updated or has been updated to reflect the new
architecture, right?

Remind me, are there no FRED systems out in the wild today, so we don't
have to worry about breaking anything?