From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EB6781E89C; Wed, 13 Aug 2025 21:59:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755122343; cv=none; b=ofmysM2986igu4ycPI0LHhQT0W2SjUBg1tQzeFgciI34w1gDTChqnQwdjInl4oCG1JSyzzYlc9hswcqPzrOmKxe3gqq3ni26E0x4Moy6vI4Qvm0yGrcHKlpMwiFE/0AFUyN/tXiRIl/1gi6mZebQrVv2nB3TOm5c1PRyhkViBB0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755122343; c=relaxed/simple; bh=7uGLGYdsjfx6KGSsceGFnWc45LxnvnvtnTpjtN4oVTY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XdEqTiWmVgCroOlQ0wNqCYQ6iFYYwnwjppomNCs4pw9pLLWWCunwvZK7CVlIcsleMU2PEBV8om8VvYgWAJYFXOAmu1/XloxhQ5yoiXLcvb2JRGvtquSHRYcKgR8GeuzCbbtR0ddk6XMuMSL4fTAIMPN12h6G0rbqjefFLzaDSks= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=lxDS+N9M; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="lxDS+N9M" Received: from [IPV6:2601:646:8081:9484:5b47:dac3:aa45:a64a] ([IPv6:2601:646:8081:9484:5b47:dac3:aa45:a64a]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 57DLw06P765108 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Wed, 13 Aug 2025 14:58:00 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 57DLw06P765108 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025072201; t=1755122281; bh=nXQBTwyqB9t6cpucEWceyx0dfvy5zDVB162E3UNuLpw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=lxDS+N9MyCNsYt8DOQ+03VTIw/0a6vDSD868tOXlwtUOiQRqMgbWIsTtXb0tpDHWf PuK5v/A6NwdLcZo8pw5ehl/yiQ4XCDayVljOQL33q7oEb/ZqWXTYhguh4ddqnoIU2Z +QFAw4sXBsB7K2F1Utp67RbFIkDuwxfztN8LNn3whdfBNgSvfzSs6y4c1mEJcUv74Z YR9EsQXQoofmgx2O5nmoNhoL26Da8k20BUt0OGyg/NNVJ2uNxsxSnubKPX0M0H0kfk Na8Ctm+iHWuCIWyxljQ8S1/I6YliPqCVUWG1jHhBSEnc3pqMD9MC4j6ACiSBX4T3GF eDLHd0vAOxcMg== Message-ID: Date: Wed, 13 Aug 2025 14:57:55 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/1] x86/fred: Remove ENDBR64 from FRED entry points To: Dave Hansen , "Xin Li (Intel)" , linux-kernel@vger.kernel.org Cc: luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, jmill@asu.edu, peterz@infradead.org, andrew.cooper3@citrix.com, stable@vger.kernel.org References: <20250716063320.1337818-1-xin@zytor.com> Content-Language: en-US From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2025-08-13 14:07, Dave Hansen wrote: > 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? Correct. The FRED v9 spec contains this change. All production hardware and late pre-production hardware will have this. -hpa