From nobody Sun Apr 12 22:38:36 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; envelope-from=xen-devel-bounces@lists.xenproject.org; helo=lists.xenproject.org; Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org; dmarc=pass(p=reject dis=none) header.from=citrix.com ARC-Seal: i=1; a=rsa-sha256; t=1775726374; cv=none; d=zohomail.com; s=zohoarc; b=TbSI8vU0pFLqrHAvaTWwlIdI707aztQPUaECwGXw/aAJsDLi93eOSxBx4NK440tEaqCfA/HoZk6eIaAUjxM1j+3TYYuUwaohpVSNhg0E4AD5rsysIYbN/o1OQ+hHxe7VSrqTa8Ut6yi9kMvm5klh9/f66e+mFho5uPUIJ3Dc+LQ= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1775726374; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:List-Subscribe:List-Post:List-Id:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:Subject:To:To:Message-Id:Reply-To; bh=MeW50FrCL89/SWSL+Q6lRGl8B2jbdOOHYY2YroAYS5w=; b=Ui/CO5cE/3U5QGgienxqUkTgZLE157Af0ZjJY258solftMYHW9DeNFgA9EdDefwxIW+XIfyxlI+QXOkwP5i6bgGDE65znz7Q/KMY7FJ0Yw+wwqTXY/HyRy3tAW5RR63mmZz5E8CIqSzwz8WJip6e8P8x0PFvqrWzC+l/LrzhA3U= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org; dmarc=pass header.from= (p=reject dis=none) Return-Path: Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) by mx.zohomail.com with SMTPS id 1775726374659262.2898465611835; Thu, 9 Apr 2026 02:19:34 -0700 (PDT) Received: from list by lists.xenproject.org with outflank-mailman.1276886.1562176 (Exim 4.92) (envelope-from ) id 1wAlXL-0005ER-Nh; Thu, 09 Apr 2026 09:18:55 +0000 Received: by outflank-mailman (output) from mailman id 1276886.1562176; Thu, 09 Apr 2026 09:18:55 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1wAlXL-0005EK-Kf; Thu, 09 Apr 2026 09:18:55 +0000 Received: by outflank-mailman (input) for mailman id 1276886; Thu, 09 Apr 2026 09:18:54 +0000 Received: from mx.expurgate.net ([195.190.135.10]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1wAlXK-0005EE-7R for xen-devel@lists.xenproject.org; Thu, 09 Apr 2026 09:18:54 +0000 Received: from mx.expurgate.net (helo=localhost) by mx.expurgate.net with esmtp id 1wAlXJ-000xTX-Ea for xen-devel@lists.xenproject.org; Thu, 09 Apr 2026 11:18:53 +0200 Received: from [10.42.69.7] (helo=localhost) by localhost with ESMTP (eXpurgate MTA 0.9.1) (envelope-from ) id 69d76efb-bab6-0a2a0a5309dd-0a2a4507afc6-4 for ; Thu, 09 Apr 2026 11:18:53 +0200 Received: from [209.85.221.48] (helo=mail-wr1-f48.google.com) by tlsNG-ef75cf.mxtls.expurgate.net with ESMTPS (eXpurgate 4.56.0) (envelope-from ) id 69d76efd-ba2d-0a2a45070019-d155dd30acd6-3 for ; Thu, 09 Apr 2026 11:18:53 +0200 Received: by mail-wr1-f48.google.com with SMTP id ffacd0b85a97d-43b983bb07eso368186f8f.0 for ; Thu, 09 Apr 2026 02:18:53 -0700 (PDT) Received: from localhost.localdomain (host-78-146-242-105.as13285.net. [78.146.242.105]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43d1e4d2971sm64967102f8f.22.2026.04.09.02.18.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Apr 2026 02:18:51 -0700 (PDT) X-Outflank-Mailman: Message body and most headers restored to incoming version X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" Authentication-Results: eu.smtp.expurgate.cloud; dkim=pass header.s=google header.d=citrix.com header.i="@citrix.com" header.h="Content-Transfer-Encoding:MIME-Version:Message-Id:Date:Subject:Cc:To:From" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1775726332; x=1776331132; darn=lists.xenproject.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=MeW50FrCL89/SWSL+Q6lRGl8B2jbdOOHYY2YroAYS5w=; b=vX8t6hJ4U/kL/f9D0+fCyO5zyStyzoxXgNVRGhj98Bo3ankwEYco1ymjFKY4wr5b+a YMC5/h7qtd+kn10wQjeo0JnKmQhjiuv/cvL/7rfeIBuaYeYxae+ciyXC9P4Ajp8JGDZH NQcWVGsXwgbClv/qZ6+raD7ZxiZd9ZO165ejw= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775726332; x=1776331132; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=MeW50FrCL89/SWSL+Q6lRGl8B2jbdOOHYY2YroAYS5w=; b=LvM20OnjEn+OFALECgiiQMl5LpCmBHTsqa1eBAGBh1/Q4VmA6qChEMJ9gytxymSBpR Tk4AMkSuXJBuNIr1UE0VqaFIyLy1arBpVwv7jw+BD1ODUcFnbbQ+OZl1B2AaXKEwO3vy ivu0cVc4bgEP88Pz8MNWBy6FcPseJf1d5jhLlao8DfO+Xa3tTmp2ZeuyaK+XtiyFRC6e rPJ+eVPYwj5URYVDcrmZ4tXy52Sd7TD1ujF5Wm+kmfBDMlLfBPAQmUDV7VvRUn8QTzpc qZ1qt/5BqjcDlXpqbSYTSb0diX1CgG1VQ5NvvhjW5QcidoPPD4rH9BtepjY8FkKdm1a/ 0q+w== X-Gm-Message-State: AOJu0YyXcMcck1tYD+Qn2gJ6D4EZIHOrvdkNi1Lf6HoQGwMBdZFTvE1C KK5PQ+jmpGx/Bcr0RxSpf7s3egngFwY5uQ98zi/uMXHjodwoGymKCH0/HbLy593WzK5eZ0AfrCA ah/rl X-Gm-Gg: AeBDiev7xsQlG4uZtI0uS0q57KHvLR5ykSaBE9Jq9Mk//n2qxvRNctD1kneY1fA5hgh iL7qcizoEzaro9UAHxIYFWL7O8bZtzdwQF7NmDBR9lE1Liv2FxOkAk/4sP/JIBCfXTCe1q32J+9 F9AmZmwO8Y45E49PbqjLoSfH92Dp2nq18K9/0ro8lsxubTo5PRUcKtlZ64nAQb1nL7B92xANRiu 1QoZPcchUYSHcu1sVfNJuOecmmqPezdJNwpPugfPyUWwpBVi0+lXkdUwcJdCNApEayJVNihc+8g 6e5v5me+V1fJLg4YQi/ugCRIUbBZsJASoI5sKMThOi2Ut2lOpQADedckwRBbKKS3O0wpaPaZXiX 4/z+Nz+05gkKMVwSw+Axrk0rNTqnK+ql0mpVen1qn8Bkrkf9D1XIpHglXHQT+K3wfnIN9f+pbKt osuwE3Cr8P3SH27rdzwjSENuwHdZYwwP2+CokuBxFqV201AreP9WkxTzN/6A4tR0flyjqY6tGnN HGN X-Received: by 2002:a5d:5d0f:0:b0:43b:3d54:3154 with SMTP id ffacd0b85a97d-43d29277113mr34409087f8f.7.1775726331570; Thu, 09 Apr 2026 02:18:51 -0700 (PDT) From: Andrew Cooper To: Xen-devel Cc: Andrew Cooper , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , Teddy Astie Subject: [PATCH] x86/pv: Adjust the save_segments() comment regarding MSR_GS_SHADOW Date: Thu, 9 Apr 2026 10:18:48 +0100 Message-Id: <20260409091848.139077-1-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.39.5 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-purgate-ID: tlsNG-ef75cf/1775726333-8B34C41E-6AAA552B/0/0 X-purgate-type: clean X-purgate-size: 1409 X-ZohoMail-DKIM: pass (identity @citrix.com) X-ZM-MESSAGEID: 1775726375876158500 This is slightly stale mentioning SWAPGS and not LKGS. However, take the opportunity to make the comment more general and less likely to bitrot. It would be a serious vulnerability for operating systems generally if CPL3 could modify GS_SHADOW at all. No functional change. Signed-off-by: Andrew Cooper Reviewed-by: Teddy Astie --- CC: Jan Beulich CC: Roger Pau Monn=C3=A9 CC: Teddy Astie --- xen/arch/x86/domain.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c index 1151997758c6..592530e53bcc 100644 --- a/xen/arch/x86/domain.c +++ b/xen/arch/x86/domain.c @@ -1952,9 +1952,8 @@ static void load_segments(struct vcpu *n) * changes to bases can also be made with the WR{FS,GS}BASE instructions, = when * enabled. * - * Guests however cannot use SWAPGS, so there is no mechanism to modify the - * inactive GS base behind Xen's back. Therefore, Xen's copy of the inact= ive - * GS base is still accurate, and doesn't need reading back from hardware. + * Guests cannot modify the inactive GS base behind Xen's back. Therefore + * Xen's copy is still accurate and doesn't need reading back. * * Under FRED, hardware automatically swaps GS for us, so SHADOW_GS is the * active GS from the guest's point of view. --=20 2.39.5