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 E605325525E for ; Tue, 15 Apr 2025 22:12:53 +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=1744755175; cv=none; b=Y48ETp9ntTYEZ0TdTZZk/J900VNeIAqWFt8g+8rl1UImn/pqLzxSq9gfYEB9L5a+rpcd6o4X+djGH8dgBtGJZ5mtn0MnbPe74m72U/iD5XDQ4brtbR0GhgZ14jidLgDdq/bE5UKJT7LBE3pHaIaCs5ILktjPjS+D4YR3EWj+y+U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744755175; c=relaxed/simple; bh=OA6xI7hqO5jrJ8K575jApn7TkXssdd7vTrMbDXVITdc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aB0OLKKbTciQSqm1lsH5CPqt1xY/yIH/6dyLTxvorsX06VaOHq2Qd8pihKuS8Plagk1B+VY6oP48ITWJ8GyntbpFGmsb0Nx8h0r0LRrF6ZYsHA6TRRf3Yzz+uGH3cPQEehkeG9QelwlVk4I7MK/4UlqBVr6dWZAJwgjBshMD52o= 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=Y9+kIl2p; 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="Y9+kIl2p" Received: by mail-wm1-f51.google.com with SMTP id 5b1f17b1804b1-43d07ca6a80so29583895e9.1 for ; Tue, 15 Apr 2025 15:12:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1744755172; x=1745359972; 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=Glra7fMFRLxrPIzQwxk8Qeb1or+7AFryoPxji38Wm8U=; b=Y9+kIl2pTvTNtKptfWoXwbO4WfA4ZnV/MmkRAY8mNJgHO8wWh8fhkTL9ta5oNI3gAP JyX5jtNeFFi6qnWvzUC+W+K1+LaizCj2/2MkD2dF68VRSF7rkthebLJTOYHaCXTwO9MH HzjMHr03lDL5cNmXgTrIajzH7dzLPfRarVLOQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1744755172; x=1745359972; 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=Glra7fMFRLxrPIzQwxk8Qeb1or+7AFryoPxji38Wm8U=; b=dpX/EWfRrmmu3wKtFdluCpo/9bJnay939wT5MeQLeWiv/NwqwJ5n8IBd+3clHDlUad BzJTvQgFqhDRRJ0dcfACWlRgNXZ6AHux1EPE6pHflaQnU60KPTsQe4X6sTIQJqvxZwdr 6cYPyAEKTlZOU5tUrvQIoGQyWiF5QukGmQY7pDY2ky29hIKK8/PcnOisyiOxqJYOJBFK nF5ymYSW58tUuK73vJOMUntqi/vCjuwM3/IORs7PJuzkF5jXdJQfMZOst742alnN7DyF rBAhJ9jf7moBT+ACLupBnqwRsPgAC8dFSs4aboqfoswDwGLEEGgp+hDDNnOsKGKfV9jM g0DA== X-Gm-Message-State: AOJu0YylskqXvsRPqZF39uID7V0u1BsTlokSidFKLk4/ZG9fpxiSYM/O Uef5lyx8vcTwd1OWlN5/IKI21hia4+Q+WVHeuJRlSfE62ZyNZiDAenNv625dwRA= X-Gm-Gg: ASbGncv1acZ013CGaAUawiPUgehBRtBOSxpJ5hre6+p5/+bbAouO5upIv2p0w5LY315 EnS5vjqMx+TALkV3eNRHKktRbsazLaNPvmSaW/RqqrWa9/pem7zrhKE7iTHuj2Ko3gsKxaSeSgv IrJe6OtkvviI0abZcejSGOnxWso+D1qt2k4LT6+VbnASQn3qD1ImC8ejiwT2WDmsh9RkBxzj+DT ON8NxDW1MdmsgWq/WasSN47F5pLD7/nj6YY+rq/5RTTEXaXS1fX/VKdgFUnVSdh5auJEuJZ13v/ 2Xs+kt/rMe4qCgQqmAt4Vv2AQERknNR9q19qKcwlRrWelvSpMZK53PVIU1BP7CAzuwGcKy2W7Xi mBUBmkg== X-Google-Smtp-Source: AGHT+IHMt3F9pL0n8daCGA27MStUQTKqmwZC5+FBFhrh37dgHkJZdg1MMLEuJ5Tc1qMw2mZGLdp7Bg== X-Received: by 2002:a05:600c:3ca0:b0:43d:fa58:8378 with SMTP id 5b1f17b1804b1-4405a0ec7cbmr5103475e9.33.1744755172019; Tue, 15 Apr 2025 15:12:52 -0700 (PDT) Received: from [192.168.1.183] (host-92-26-98-202.as13285.net. [92.26.98.202]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4405b4f2cfesm2246405e9.19.2025.04.15.15.12.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Apr 2025 15:12:50 -0700 (PDT) Message-ID: Date: Tue, 15 Apr 2025 23:12:49 +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: [PATCH v13 09/19] x86: Secure Launch kernel early boot stub To: Sean Christopherson , Ross Philipson Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-integrity@vger.kernel.org, linux-doc@vger.kernel.org, linux-crypto@vger.kernel.org, kexec@lists.infradead.org, linux-efi@vger.kernel.org, iommu@lists.linux.dev, dpsmith@apertussolutions.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, ardb@kernel.org, mjg59@srcf.ucam.org, James.Bottomley@hansenpartnership.com, peterhuewe@gmx.de, jarkko@kernel.org, jgg@ziepe.ca, luto@amacapital.net, nivedita@alum.mit.edu, herbert@gondor.apana.org.au, davem@davemloft.net, corbet@lwn.net, ebiederm@xmission.com, dwmw2@infradead.org, baolu.lu@linux.intel.com, kanth.ghatraju@oracle.com, trenchboot-devel@googlegroups.com References: <20250410204149.2576104-1-ross.philipson@oracle.com> <20250410204149.2576104-10-ross.philipson@oracle.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/04/2025 10:40 pm, Sean Christopherson wrote: > On Thu, Apr 10, 2025, Ross Philipson wrote: >> + * instruction can return for a number of reasons. Test to see if it returned >> + * because the monitor was written to. >> + */ >> + monitor >> + >> +1: >> + mfence >> + mwait >> + movl (%eax), %edx > Why load the value into EDX? At a glance, the value is never consumed. > >> + testl %edx, %edx >> + jz 1b > This usage of MONITOR/MWAIT is flawed. The monitor needs to be re-armed in each > loop, otherwise mwait will be a glorified nop. > > More importantly, the exit condition needs to be checked before monitor, after monitor and before mwait. But yes, the prior logic was definitely wonky. > even on > the first iteration. In the (probably extremely unlikely) scenario that the write > to wake the CPU arrives before MONITOR is executed, this CPU may get stuck waiting > indefinitely. > > E.g. something like: > > > 1: > monitor > cmpl (%eax), 0 $0 Luckily, this will fail to assemble, rather than dereferencing 0. ~Andrew > jnz 2f > mwait > jmp 1b > 2: