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 8271EC3DA4A for ; Mon, 29 Jul 2024 17:52:05 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.767057.1177623 (Exim 4.92) (envelope-from ) id 1sYUX2-0003Wr-QG; Mon, 29 Jul 2024 17:51:36 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 767057.1177623; Mon, 29 Jul 2024 17:51:36 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1sYUX2-0003Wk-Nf; Mon, 29 Jul 2024 17:51:36 +0000 Received: by outflank-mailman (input) for mailman id 767057; Mon, 29 Jul 2024 17:51:35 +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 1sYUX1-0003We-SW for xen-devel@lists.xenproject.org; Mon, 29 Jul 2024 17:51:35 +0000 Received: from mail-wm1-x32f.google.com (mail-wm1-x32f.google.com [2a00:1450:4864:20::32f]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 316157ee-4dd3-11ef-8776-851b0ebba9a2; Mon, 29 Jul 2024 19:51:33 +0200 (CEST) Received: by mail-wm1-x32f.google.com with SMTP id 5b1f17b1804b1-4281f00e70cso7820605e9.1 for ; Mon, 29 Jul 2024 10:51:33 -0700 (PDT) Received: from [192.168.1.10] (host-92-26-98-202.as13285.net. [92.26.98.202]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36b367d9576sm12952910f8f.31.2024.07.29.10.51.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Jul 2024 10:51:32 -0700 (PDT) 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: 316157ee-4dd3-11ef-8776-851b0ebba9a2 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1722275493; x=1722880293; darn=lists.xenproject.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=jF1MrwtNaChbQg+KF324+dQeLVOpu3FAPmGNawyI/1Q=; b=Uz6+CbDq/j5oxRphMfigofNroaK2cB2dAmu4/vPMdOQ1cUgAwHIukb78wpBVQNZiTJ XXHnu7V9Mx7s9F0QJz7sldip6hkXgb/9RzbrSxtl4Ef4WmYJAvqB7QFGgwnBscrSS6xs 8w/OWpvM8qY9HwRXRR1gVbHYqBfftOa2S6U0g= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722275493; x=1722880293; 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=jF1MrwtNaChbQg+KF324+dQeLVOpu3FAPmGNawyI/1Q=; b=woLAVdWqFH+GCX87E2V4SNlJBIr23F18/LoO9VZFe/bPgu4wSlEyUA32t1S19k/33a 2RS6bdqehw1eZwLPlXYDu4d6BAd4yDWewoDuICDntadWnnKRCId7Ou/VF/OV76a11zyn shkFMiD9jz8vdmyZsjgrVi2SBaQNsqc0vCIwDiaajeRyK2X4ECdVQGh78ad4nXgeWHdo tHw3d2qFM7cRix7dKukTudyQr2Osn/AKZPfEtw1uY67bub45KnGiDajwHSF6eDiUvF1a NV9iNV6akJHlCr/zBfoXLiT1n29KgQlSHdgT0Dm8dwZk7IXsttdTuIkGr9psuzCRa0Fh NiLw== X-Forwarded-Encrypted: i=1; AJvYcCX4MKXMeMqJS5fZTwVSyvkGQWjXQxIYwSniOoi5L8tsc076zt6pKpK4HuGDYYTM5BLEJTCLAGXeHMOogdCuYk9rcVYhvpPL3diQSY/6cWs= X-Gm-Message-State: AOJu0Yyc4deIeCJfKwtd6m3NBnpETBR0ewUiGagTy8ZwbrNR/rkfZZbx D619t6suD11R2JGm3LmKv76BpkUIYM6ukWpfGeLbi/QStUCRa/UQ3qMKSpOLs+U= X-Google-Smtp-Source: AGHT+IFgZReSXzQR3V1ms2jn3NdMEb51xhy/KS6cshqTc8JauKclPeJJrUt+UIFPwZIH3w5DbCImPg== X-Received: by 2002:a5d:6787:0:b0:362:d382:2569 with SMTP id ffacd0b85a97d-36b5d08f68bmr5297976f8f.44.1722275492705; Mon, 29 Jul 2024 10:51:32 -0700 (PDT) Message-ID: <542807c8-425b-481f-b02f-dd657c12ef5d@citrix.com> Date: Mon, 29 Jul 2024 18:51:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/22] x86/dom0: only disable SMAP for the PV dom0 build To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: Jan Beulich , alejandro.vallejo@cloud.com, xen-devel@lists.xenproject.org References: <20240726152206.28411-1-roger.pau@citrix.com> <20240726152206.28411-4-roger.pau@citrix.com> <5aad5f48-e32e-4a59-bcef-05adec0ecbec@citrix.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: 8bit On 29/07/2024 5:18 pm, Roger Pau Monné wrote: > On Mon, Jul 29, 2024 at 04:52:22PM +0100, Andrew Cooper wrote: >> On 29/07/2024 12:53 pm, Jan Beulich wrote: >>> On 26.07.2024 17:21, Roger Pau Monne wrote: >>>> The PVH dom0 builder doesn't switch page tables and has no need to run with >>>> SMAP disabled. >>>> >>>> Put the SMAP disabling close to the code region where it's necessary, as it >>>> then becomes obvious why switch_cr3_cr4() is required instead of >>>> write_ptbase(). >>>> >>>> Note removing SMAP from cr4_pv32_mask is not required, as we never jump into >>>> guest context, and hence updating the value of cr4_pv32_mask is not relevant. >>> I'm okay-ish with that being dropped, but iirc the goal was to keep the >>> variable in sync with CPU state. >> Removing SMAP from cr4_pv32_mask is necessary. >> >> Otherwise IST vectors will reactive SMAP behind the back of the dombuilder. >> >> This will probably only manifest in practice in a CONFIG_PV32=y build, > Sorry, I'm possibly missing some context here. When running the dom0 > builder we switch to the guest page-tables, but not to the guest vCPU, > (iow: current == idle) and hence the context is always the Xen > context. Correct. > Why would the return path of the IST use cr4_pv32_mask when the > context in which the IST happened was the Xen one, and the current > vCPU is the idle one (a 64bit PV guest from Xen's PoV). > > My understanding is that cr4_pv32_mask should only be used when the > current context is running a 32bit PV vCPU. This logic is evil to follow, because you need to look at both cr4_pv32_mask and XEN_CR4_PV32_BITS to see both halves of it. Notice how cr4_pv32_restore() only ever OR's cr4_pv32_mask into %cr4? CR4_PV32_RESTORE is called from every entry path which *might* have come from a 32bit PV guest, and it always results in Xen having SMEP/SMAP active (as applicable).  This includes NMI. The change is only undone in compat_restore_all_guest(), where XEN_CR4_PV32_BITS is cleared from %cr4 iff returning to Ring1/2.  This is logic cunningly disguised in the use of the Parity flag. Because the NMI handler does reactive SMEP/SMAP (based on the value in cr4_pv32_mask), and returning to Xen does not pass through compat_restore_all_guest(), taking an NMI in the middle of of the dombuilder will reactive SMAP behind your back. ~Andrew