From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1EB8AC77B73 for ; Mon, 5 Jun 2023 13:52:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234027AbjFENwI (ORCPT ); Mon, 5 Jun 2023 09:52:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231744AbjFENwG (ORCPT ); Mon, 5 Jun 2023 09:52:06 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E64B9EE; Mon, 5 Jun 2023 06:52:03 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1685973122; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=uUOQseh5ydTYez7B9hZObsjFUYK1akvdtGONm9fjmIs=; b=mbNws8bz4std+L0u9Lf4aoWUTjvU2jIPojtqquY0d3WuwiPvHrZn7v72Y65DI+hjDtA1u9 d6ibnkPXRtwGMDquSWuGVT3TgIxrKmOs7mzQtZfdWHxKeJRg31xoGy1wO4rvgMU6iuWrlN u+PLzsZji8C10UQTkYPxqk+gk+2tzsM257e5cSr1Xcfc+Fg51FTarTDTyNHN61lJjtSlOG rhWo9Q1cQMJzYqfFjccniJAPw4Jd83KSQKuoamVtsbz/Ns92GjAYCxWjumWrOtMenIRZnc KrWkaIlWJBVbRSrND3iGKmX2gmuG5ZTIDlEHI/l08SQe2oKFbkrL/3jgaxMcpQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1685973122; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=uUOQseh5ydTYez7B9hZObsjFUYK1akvdtGONm9fjmIs=; b=BNUdCmLWcHQfE4V/dctZz8skLLVebFyHPvaS9VJ/LM+GbyQuO/7QciA8XWv8PdmFh+SWL5 VvGLhnCWuFVD38Dg== To: Xin Li , linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org Cc: mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, peterz@infradead.org, andrew.cooper3@citrix.com, seanjc@google.com, pbonzini@redhat.com, ravi.v.shankar@intel.com, jiangshanlai@gmail.com, shan.kang@intel.com Subject: Re: [PATCH v8 26/33] x86/fred: allow single-step trap and NMI when starting a new thread In-Reply-To: <877csi6mrk.ffs@tglx> References: <20230410081438.1750-1-xin3.li@intel.com> <20230410081438.1750-27-xin3.li@intel.com> <877csi6mrk.ffs@tglx> Date: Mon, 05 Jun 2023 15:52:02 +0200 Message-ID: <874jnm6mpp.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 05 2023 at 15:50, Thomas Gleixner wrote: > On Mon, Apr 10 2023 at 01:14, Xin Li wrote: >> Allow single-step trap and NMI when starting a new thread, thus once >> the new thread returns to ring3, single-step trap and NMI are both >> enabled immediately. >> >> High-order 48 bits above the lowest 16 bit CS are discarded by the >> legacy IRET instruction, thus can be set unconditionally, even when >> FRED is not enabled. > > I assume this has been validated to be true on _all_ CPU incarnations of > _all_ x86 vendors. It's also ensured that VMMs do not get confused by this, right? > If so, then please document it. If not, then go back to the drawing > board. > > Thanks, > > tglx