From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f51.google.com (mail-wm1-f51.google.com [209.85.128.51]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C0392F9C3A for ; Fri, 15 Aug 2025 17:21:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755278513; cv=none; b=c3q6Hr0PA7ajLV4RuT9MhsecbGy9nWWicw3XSe1fJhvi7KmNw+gko6NOIpslqKJIdtI7HxK5QjGPVDaMoeHgPykuJKx6oJd/HLkSQJtpn6esQvz86oKw8ihXMG7X+gOlRy12bJKStKuE98QNC5xYaIEqSekNXwjXX4fBwdl1kis= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755278513; c=relaxed/simple; bh=4ZL0bRDd8O9uSHfWegdNoycSbwD4KpHOyXInfbC9h7k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=p6mDItTq8hzTmnWVEnmBLzbx21KAmny24+IlUiCHGou9GQXWtAzHP1OyHgUoC0xYx8fe3iVqw72G0iX/oDqUTQwpgWJAtxZmTk+oIk+shqFRdgY/NIu1PBx+g1pHDDUNOkPfGyIzce3mRo0wqUA4dAhFKS7aJtY98/F3ASYNYEA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=citrix.com; spf=pass smtp.mailfrom=cloud.com; dkim=pass (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b=iLEkY89z; arc=none smtp.client-ip=209.85.128.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=citrix.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=cloud.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b="iLEkY89z" Received: by mail-wm1-f51.google.com with SMTP id 5b1f17b1804b1-45a1b0cbbbaso14783925e9.3 for ; Fri, 15 Aug 2025 10:21:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1755278510; x=1755883310; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:from:to:cc:subject:date:message-id:reply-to; bh=4ZL0bRDd8O9uSHfWegdNoycSbwD4KpHOyXInfbC9h7k=; b=iLEkY89ziLc+D0yfDM4njI5FxTsbqqteLb/msTh3o2JYS3ijlhuwzs1O8FMXVyKyDi ubmkawJRwPRwc7jXu1ZSqYEIvJxXfmeNMWSAkm5nu7XWEdDD8umuS4FW+aipCgCZ7KsD Ku3XVIk0Lk7E81FLcNyuW5rSd0WoQ2oJvexBs= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1755278510; x=1755883310; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=4ZL0bRDd8O9uSHfWegdNoycSbwD4KpHOyXInfbC9h7k=; b=MG/2z1XItLpuqzOoHO8brwlpmoOcj6K2HnxysNs4yWQ9w4ynpYZcURKXtZE2pB74W5 1RubYOCjIkQOQlwcfU0S1+M2/1vLg3+G4jzeraWbqdFtthxgGqRYjvO+Q/ZJq/+w1SK+ TzXL72iwQEBNpNn5BdtKFrNaY2HrjUNdD1+BtMuHeQ0R/bIZJmP3Xh7v04SUWwKuYvgb fLHC9toSHCT4IYDYETTXas1IU5+oj9VTuj+TEQg6XgY79lh276J4DGmTHYFEOzDttOYe BaT7te021gGibcAS55gjyAYEP5U0oDW0elEod3MQtRyiipec5Kmj+s1C6aFSPc/Lxz6J +kPA== X-Forwarded-Encrypted: i=1; AJvYcCWivdS0pTljxlcogVpGsWMt7TmG1IEsPDVLSsUDnAo9gM9aNEbs75Sit4hxY2lXwxuNagk068AWqJ/RbnY=@vger.kernel.org X-Gm-Message-State: AOJu0YySY3xVp9lYCSUDd/RXiPQCyphsrGuJOPUP4Ehm5M/5EWVcuKFj ObFIc5rMM9VaA7OQdmbclasbDSEkQSnjyJRUNir8rm7EgrSN/d/4Wx9CgmLTK6hBXIM= X-Gm-Gg: ASbGncv0VvzqSfdUNnzgorJyJzTfmn5hIfOoqWQtBtHN0TmFnfLEkKzR8Ap2CC7E+4q UTFixflzxmIBU46ZrBXRS8M+thYN/FaYCBKjFIrNXXOIGu08dM1ZMjyLf+Tj8RTF/BQcAaHjmNd pub2XAhN+LedfIxzVUCqwVQCgiYEfOWjPRvjEWPuPaggsLiz+4A0XcbT1ZYcRLr89KuKibXbrQy wH8jemg4L0WYSv7A+yaG6HDlrEmU6Hg2edw7GoAay0DlDEQbNMGiEJ4o3EtJ9CIYsvSxjNoyLSi iAkIPFI0ijZvC3ZMPibcI2JyuVPCOphxo9vQopCd6RCPeP7hCyeDLEtL/OXpdn4bKT8hqvUzAvX uD523HtFJdE0OWRVoH9bI+k7zWeIWtuXkw6zV27km1ipdxCU9lic0XQsCci03ajFBISor X-Google-Smtp-Source: AGHT+IFLpF5jMiMYrRRBHdAiBCob7Fl8EGquPFWrJyKnNndR/zM6RtCW2pKmmcymsSU333i3DF1edQ== X-Received: by 2002:a05:600c:19d3:b0:459:df25:b839 with SMTP id 5b1f17b1804b1-45a2186e2c2mr20864005e9.33.1755278509683; Fri, 15 Aug 2025 10:21:49 -0700 (PDT) Received: from [192.168.1.183] (host-195-149-20-212.as13285.net. [195.149.20.212]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45a21aa51cesm18029915e9.1.2025.08.15.10.21.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 Aug 2025 10:21:49 -0700 (PDT) Message-ID: <7594ecd7-994d-4cb8-9f8a-b6c1d4b01e17@citrix.com> Date: Fri, 15 Aug 2025 18:21:48 +0100 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: [RFC][PATCH] x86,ibt: Use UDB instead of 0xEA To: "H. Peter Anvin" , Peter Zijlstra Cc: x86@kernel.org, kees@kernel.org, alyssa.milburn@intel.com, scott.d.constable@intel.com, joao@overdrivepizza.com, samitolvanen@google.com, nathan@kernel.org, alexei.starovoitov@gmail.com, mhiramat@kernel.org, ojeda@kernel.org, linux-kernel@vger.kernel.org References: <20250814111732.GW4067720@noisy.programming.kicks-ass.net> <2c121572-8fde-4288-80ca-ab79f2b22cce@zytor.com> <20250815074939.GA3419281@noisy.programming.kicks-ass.net> <20250815102839.GD4068168@noisy.programming.kicks-ass.net> <20250815103055.GE4068168@noisy.programming.kicks-ass.net> <20250815105908.GB3245006@noisy.programming.kicks-ass.net> <055f4c2b-0e7f-44ae-92ff-a1025a217208@citrix.com> <78bd985a-a59e-4469-a84d-a0eb7faa20c3@zytor.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: <78bd985a-a59e-4469-a84d-a0eb7faa20c3@zytor.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 15/08/2025 6:14 pm, H. Peter Anvin wrote: > On 2025-08-15 04:19, Andrew Cooper wrote: >>> CS Jcc, decodes to Jcc,pn for non-taken >>> DS Jcc, decodes to Jcc,pt for taken >> Ah, thanks.  I was looking at the hex in one of the comments and still >> couldn't figure it out. >> >> So with this notation, we also have the dual meaning of ,pt between the >> P4 and LNC.  At least the encoding is the same. >> > What "dual meaning?" Well, it has different semantics now it's been reintroduced in LNC.  (Only has any effect on a prediction miss, and causes a proactive decode resteer). Sure, it's "just perf" so can be argued as "compatible behaviour", but people caring about the ,pt / ,pn properties do need to know the different. ~Andrew