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 lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 51761C46CCD for ; Mon, 18 Dec 2023 12:39:44 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.655964.1023864 (Exim 4.92) (envelope-from ) id 1rFCtr-0003FX-FO; Mon, 18 Dec 2023 12:39:11 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 655964.1023864; Mon, 18 Dec 2023 12:39:11 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1rFCtr-0003FQ-C1; Mon, 18 Dec 2023 12:39:11 +0000 Received: by outflank-mailman (input) for mailman id 655964; Mon, 18 Dec 2023 12:39:10 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1rFCtq-0003FK-KS for xen-devel@lists.xenproject.org; Mon, 18 Dec 2023 12:39:10 +0000 Received: from mail-wm1-x332.google.com (mail-wm1-x332.google.com [2a00:1450:4864:20::332]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 6fccf1c9-9da2-11ee-9b0f-b553b5be7939; Mon, 18 Dec 2023 13:39:08 +0100 (CET) Received: by mail-wm1-x332.google.com with SMTP id 5b1f17b1804b1-40c339d2b88so31768435e9.3 for ; Mon, 18 Dec 2023 04:39:08 -0800 (PST) Received: from localhost ([213.195.127.70]) by smtp.gmail.com with ESMTPSA id t9-20020a05600c198900b0040c490db950sm31553236wmq.47.2023.12.18.04.39.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Dec 2023 04:39:07 -0800 (PST) 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" X-Inumbo-ID: 6fccf1c9-9da2-11ee-9b0f-b553b5be7939 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1702903148; x=1703507948; darn=lists.xenproject.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=jdkKBhaUm/qQXMxDj+zOdH5N1Fpb5RPvTGS8ZYXnJl8=; b=WATgGqJwcPK5C9AeLhSB8tdKZLyKvfZYbUpMY5aLS4/L+XFnN2KAhvjTCarF74U0X5 8/xiUDok8jbj4laJ6K/PQkI1M7DPk2q7LJrxlsp2oXLlFNdWRvAL9vouiGXxKWSOVlMK H8zfFOwBpw4o0fj3/dpbbddogv1arc7fNFR7A= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702903148; x=1703507948; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=jdkKBhaUm/qQXMxDj+zOdH5N1Fpb5RPvTGS8ZYXnJl8=; b=YQxkK9W7FQP9ofIoRXEMtDkkBUQZDXIwZjZbgkpVwLV1oDCXJkYGfbYY4WZcBfANAF F+InETu9I+aMJ9EkBXd1++ir0A2YWpTHStczBBQKvbVhcmXheGpRVtdSa5ZYbXuidxjo Rx6QuUq//2G4b30WzNRqRsPvj/Cf5L8n9+YdHjnqWNX6W+Ze9S4qB1YHtBkzfM+9cY8J LGrV8NftUR3hFRdmcy6an7yO4jHMIiBnHgHozwyjLxQt3NroDuXMrvqNrD87D5fldM3b TRtkCAjbRcPbQw1ZBrXcHqliMzq9I+vo/oM9LpByM5gPY7KlyIgjGc1BjlPVlb7wIiMJ HGBg== X-Gm-Message-State: AOJu0YyD+427Ufxc9h7akzfEQ39Ngc5hlCrMToXJ4A9FyokyI1obsArx MaabnZfKXsTWG5L6VEknN0f7vg== X-Google-Smtp-Source: AGHT+IHE2Efg3G7VL9QgT1GxU9SL60uxQutRS338pKilE6s0iG6b87xzgI63f7mZyspCIaScsKmYWA== X-Received: by 2002:a05:600c:4d0f:b0:40c:3e43:417f with SMTP id u15-20020a05600c4d0f00b0040c3e43417fmr7912062wmp.58.1702903147658; Mon, 18 Dec 2023 04:39:07 -0800 (PST) Date: Mon, 18 Dec 2023 13:39:06 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Wei Liu Subject: Re: [PATCH v4 2/4] x86/spec-ctrl: defer context-switch IBPB until guest entry Message-ID: References: <06591b64-2f05-a4cc-a2f3-a74c3c4a76d6@suse.com> <83c2a504-bce4-d3e7-1d9a-76ac0ca17bab@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <83c2a504-bce4-d3e7-1d9a-76ac0ca17bab@suse.com> On Tue, Feb 14, 2023 at 05:11:05PM +0100, Jan Beulich wrote: > In order to avoid clobbering Xen's own predictions, defer the barrier as > much as possible. Merely mark the CPU as needing a barrier issued the > next time we're exiting to guest context. While I understand that doing the flush in the middle of the guest context might not be ideal, as it's my understanding we also needlessly flush Xen predictions, I'm unsure whether this makes any difference in practice, and IMO just makes the exit to guest paths more complex. Thanks, Roger.