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 2152437F01B; Mon, 23 Mar 2026 20:44:02 +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=1774298644; cv=none; b=L9YR6uD4UDXG1prMTEwAcgnpt9j+ZpQ4vDmquyLgSDp89kGQbvFCuk1Ca50LSRN3cSJUXF0ruPePDwNpOxGXkBfV9EmoOvHDmbakZEGYn+f+PderIDKmELl/PVOq52ed+jA6HeIlMNAwmY0IKpeOTeYOIiHW0ERsSIffiPKyxnc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774298644; c=relaxed/simple; bh=vXqcipqgH0S3NtrVzXRwJpgdgKtE+evTaBXC41Pu2Fs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=kKA6T9Hb+LD41oQBV951+SvX5ulokVvxke0Slr932MG5dQb6ykD3uSJ2in9M1KIVsO+Cxb4tQzIz+3VaVgo/RF0BKeJX5wWPkTXVGMvJ1V86iRUZJflGBfci9uc5Y7F+BP5oR+VdKZkyJBg8VVlzDMfQA4Ntm9rPwwoyFOe1THQ= 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=i+qODxGq; 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="i+qODxGq" Received: from [172.27.2.41] (c-76-133-66-138.hsd1.ca.comcast.net [76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 62NKRjba3137652 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 23 Mar 2026 13:27:46 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 62NKRjba3137652 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2026022301; t=1774297667; bh=BWtD0ju6ZbiaJZB565d+DPNEOTfQ40hzPlXd4Ui8O/s=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=i+qODxGqOKlYHHLnBrfAmILbKuj9Cbkp5WLvTAoLs+KhUxpK8AUtstaLw2auSnXFW J0GGSE1FyD7uCwTgqOxFoHwv81c1bWnnURD8u2+byhMRcz0OABTxJs8Yng7NIL3VkT GlPxX6zi1bBGmPLfcz22ETJG7sxRawV8b+aIX5VcYADay55+vhLBOh3Y1+6P20Ro74 QSX9VIUjDQzzB2FW1sPYXyte3AL/su1ZrXy64cnoKox82vfWOZ7VxGygqAtvEK0wcq UfqAY6R68M/ZRijcDlXQlfVhybUfnl013V1b4Z/TiQdJUawWpmQ2FlyREK4B/19D9s bofyJO5F1Xgtw== Message-ID: <0200a8d8-6871-4ff2-8c6a-968c2cb39a4f@zytor.com> Date: Mon, 23 Mar 2026 13:27:40 -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] selftests/x86: Fix sysret_rip assertion failure on FRED systems To: Andrew Cooper , "Lai, Yi" , Xin Li Cc: Dave Hansen , yi1.lai@intel.com, bp@alien8.de, dave.hansen@linux.intel.com, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, luto@kernel.org, mingo@redhat.com, shuah@kernel.org, tglx@kernel.org, x86@kernel.org References: <43f2c5c2-6327-4546-b204-5c66b704042e@citrix.com> <568aa6c4-6802-4eb5-b412-e3aa93ed9b29@intel.com> <91590BC4-A54E-40F4-A223-A07FBA386A9A@zytor.com> Content-Language: en-US, sv-SE From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 2026-03-23 12:17, Andrew Cooper wrote: > > This doesn't really test whether FRED is active.  It tests whether the > OS is not providing strict backwards compatibility, and I think will > malfunction when there's a hypervisor above Linux providing strict > backwards compatibility. > But that applies equally to IRET, no? If the hypervisor clobbers the segment selector like IRET would in the interest of compatibility then you have the same issue. If the guest is running a FRED kernel and the hypervisor goes in and mucks with the state after ERETU behind the kernel's back I think you have a much, much bigger problem. -hpa