From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f50.google.com (mail-ej1-f50.google.com [209.85.218.50]) (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 08A15185B48 for ; Tue, 25 Nov 2025 10:19:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764065978; cv=none; b=k7+TCd4XKB3EUoqt9pJN40GO9BoHgcrAmHCtCI5jPv+YU/h0PZXBJMawjJF9z8JNwv8GVL9C/pklFRVrhW3Qr26uw2dV3hBM5HreOVeWed0d2yxTaNck/BP8bJHquVfWHFRDyo4PiSnqzCjpC/LIecP+DYptwKq2q/EqKbzv00E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764065978; c=relaxed/simple; bh=73wVfPno0wQcookdVqT5/p7wBQHro2hIk0Y/VvxdwaY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YFm0zFqjf5zHG5CS5udNfej3KmGLWSFLF7V6MSgKro9c+g115NuPjrNpciSK1ddBrraLjtiZ6jfRElhN3ayE728foswFZHOe4B8/oipp32BcMbVW7Q6DoEn8IvIWsjAfmX6Qvn7THJTBWJwXBPXlmRDatqAktNyrNLtYubfV+Js= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=E9J6QlrG; arc=none smtp.client-ip=209.85.218.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="E9J6QlrG" Received: by mail-ej1-f50.google.com with SMTP id a640c23a62f3a-b734fcbf1e3so888900466b.3 for ; Tue, 25 Nov 2025 02:19:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1764065974; x=1764670774; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:from:to:cc:subject:date:message-id:reply-to; bh=yIMSsJySte+KTCdc/08zeoYNJkejZ3jDLpSNroCq3SQ=; b=E9J6QlrGFunSnz174NGZUot3dyL4gjOHCykiRdfyGFrPg3xHAoy7DwC3+8MINqfe+9 F9zVzBY5Hk8P5pLPAHyKXJHZUsyTEVm4HHMCKCVkF8RaEVGOK5n+xQ9D4nBDmAxv3mHz kJ7pxXiLO1hCpqZwIgvQGWEaxp8NTNEhwPy/rRroKqBRLCoB2EwgQbilw+w6UwZ9Do8B Ft9n3Zz5n3D2V6wGV8MMCvWV75yLlvZPfGrQ90MVbC9BCoCUmWi05CwJ0bsHB9csFWYw DlZQ0fON/YxvSvZqLoKmGC/91F6m6/cgkeg2p7OAw0NWxnAVlCLrZxo1uXYf3Soz2K36 CjZg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1764065974; x=1764670774; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=yIMSsJySte+KTCdc/08zeoYNJkejZ3jDLpSNroCq3SQ=; b=gAz6mzWhIG4NjT4uH2w/94RDmsosXMp/7bc5yUyLNcpYYsMEd4WuQNSkEGW8o6ueW0 CEcxgHzdZXPCybNJYfOD7LM0oA8r6+BIbEGfu1hRx3O756XbbodVKNxzzrr1dsC5kPKc vJ5Ryf4YXP9lksz2puFqk7Rv+EI1OWZFRd0sQcmxguzCVPDBmNPT1k5LUBlwTD4PDh7D VqtZTrvHekONWGCNt/oeh9QO/6b4dmcjkWoCW5UpPndkNbjNHoRvRhPiux0avzTS8D/P mkVt4C7dzVH94jZZ8GMmWj1mz0FW8ZthPwN4PBtbrRhd3/Q/+I4vI3seJ00qqGMPqVs9 nRAA== X-Forwarded-Encrypted: i=1; AJvYcCXMYd8ny/IZcumWxN/jC9IpiAgRd5u4LgR2W/dRuFJ0DlGxmXkUQ3G+qR8NibGjFkK0lHlBG3wotbx/VRQ=@vger.kernel.org X-Gm-Message-State: AOJu0Yw2heA4dxH0SaVQOOFbV3DPoUt3u10WqgTBMoHVYqKarh4FO9DO cUFbvnqYICZeqaqHczIrRG8aacJRTzdfuzkIZpFxkY8LUi/0EvNXFU/ZG/ooBhT0/G0= X-Gm-Gg: ASbGnctu2FpC5whmvp9iyULDyq5qRk++dUYCHhwvNz2zWTQrz/vgNuCkLUImevvbIwR uJsKHL6kgdeLy6HWL323tQKFFgYX0QggKZbxOhaJCNO9JiFW4lc7pgTCH+oabXT16/tJqmAhQPb P8iIQBzx1JxNPmdBGEZASyXCHQVThxEpqtSvqxa9NimU3tHd3c4fPgv5lZjTyh8Me1jPKbXY4L2 pcmvAbDoCICOWjPsUR7lrVn8rD2aJmvJrkDwe8HWrr8EzxliVnDPY3prw4QzpEiG+WWe9nno/nQ VFv+GJQVnTYT6L0YimE36fmpiA/Pm/Nk+6FoAyVD3Lpg2ealt84SLZni1JeeYQpsuN9cmgCEQZo m8podp5Z4JxyxIIriUk7FScgoATUbqvkHt0Hrbw892pbYV/3g9w0poHe0VOLXKbqwI0Ps4w1vll tZQhev9HYEviwus/3YbrooslnqMBFrDacTnlPE X-Google-Smtp-Source: AGHT+IGYmFskiHfa4/E1/neLmiMDPqxoViEsBkCue2XNF3bz7i8Fb3d9jLZ7gj1dYP5cXdO2qF6z9g== X-Received: by 2002:a17:906:fe47:b0:b76:2667:7717 with SMTP id a640c23a62f3a-b76718ab19cmr1737777266b.56.1764065974110; Tue, 25 Nov 2025 02:19:34 -0800 (PST) Received: from [192.168.0.20] (nborisov.ddns.nbis.net. [85.187.216.236]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b7654fd4275sm1500974766b.37.2025.11.25.02.19.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Nov 2025 02:19:33 -0800 (PST) Message-ID: Date: Tue, 25 Nov 2025 12:19:32 +0200 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 v4 06/11] x86/vmscape: Move mitigation selection to a switch() To: Pawan Gupta Cc: x86@kernel.org, David Kaplan , "H. Peter Anvin" , Josh Poimboeuf , Sean Christopherson , Paolo Bonzini , Borislav Petkov , Dave Hansen , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Asit Mallick , Tao Zhang References: <20251119-vmscape-bhb-v4-0-1adad4e69ddc@linux.intel.com> <20251119-vmscape-bhb-v4-6-1adad4e69ddc@linux.intel.com> <20251124230917.7wxvux5s6j6f5tuz@desk> From: Nikolay Borisov Content-Language: en-US Autocrypt: addr=nik.borisov@suse.com; keydata= xsFNBGcrpvIBEAD5cAR5+qu30GnmPrK9veWX5RVzzbgtkk9C/EESHy9Yz0+HWgCVRoNyRQsZ 7DW7vE1KhioDLXjDmeu8/0A8u5nFMqv6d1Gt1lb7XzSAYw7uSWXLPEjFBtz9+fBJJLgbYU7G OpTKy6gRr6GaItZze+r04PGWjeyVUuHZuncTO7B2huxcwIk9tFtRX21gVSOOC96HcxSVVA7X N/LLM2EOL7kg4/yDWEhAdLQDChswhmdpHkp5g6ytj9TM8bNlq9I41hl/3cBEeAkxtb/eS5YR 88LBb/2FkcGnhxkGJPNB+4Siku7K8Mk2Y6elnkOctJcDvk29DajYbQnnW4nhfelZuLNupb1O M0912EvzOVI0dIVgR+xtosp66bYTOpX4Xb0fylED9kYGiuEAeoQZaDQ2eICDcHPiaLzh+6cc pkVTB0sXkWHUsPamtPum6/PgWLE9vGI5s+FaqBaqBYDKyvtJfLK4BdZng0Uc3ijycPs3bpbQ bOnK9LD8TYmYaeTenoNILQ7Ut54CCEXkP446skUMKrEo/HabvkykyWqWiIE/UlAYAx9+Ckho TT1d2QsmsAiYYWwjU8igXBecIbC0uRtF/cTfelNGrQwbICUT6kJjcOTpQDaVyIgRSlUMrlNZ XPVEQ6Zq3/aENA8ObhFxE5PLJPizJH6SC89BMKF3zg6SKx0qzQARAQABzSZOaWtvbGF5IEJv cmlzb3YgPG5pay5ib3Jpc292QHN1c2UuY29tPsLBkQQTAQoAOxYhBDuWB8EJLBUZCPjT3SRn XZEnyhfsBQJnK6byAhsDBQsJCAcCAiICBhUKCQgLAgQWAgMBAh4HAheAAAoJECRnXZEnyhfs XbIQAJxuUnelGdXbSbtovBNm+HF3LtT0XnZ0+DoR0DemUGuA1bZAlaOXGr5mvVbTgaoGUQIJ 3Ejx3UBEG7ZSJcfJobB34w1qHEDO0pN9orGIFT9Bic3lqhawD2r85QMcWwjsZH5FhyRx7P2o DTuUClLMO95GuHYQngBF2rHHl8QMJPVKsR18w4IWAhALpEApxa3luyV7pAAqKllfCNt7tmed uKmclf/Sz6qoP75CvEtRbfAOqYgG1Uk9A62C51iAPe35neMre3WGLsdgyMj4/15jPYi+tOUX Tc7AAWgc95LXyPJo8069MOU73htZmgH4OYy+S7f+ArXD7h8lTLT1niff2bCPi6eiAQq6b5CJ Ka4/27IiZo8tm1XjLYmoBmaCovqx5y5Xt2koibIWG3ZGD2I+qRwZ0UohKRH6kKVHGcrmCv0J YO8yIprxgoYmA7gq21BpTqw3D4+8xujn/6LgndLKmGESM1FuY3ymXgj5983eqaxicKpT9iq8 /a1j31tms4azR7+6Dt8H4SagfN6VbJ0luPzobrrNFxUgpjR4ZyQQ++G7oSRdwjfIh1wuCF6/ mDUNcb6/kA0JS9otiC3omfht47yQnvod+MxFk1lTNUu3hePJUwg1vT1te3vO5oln8lkUo9BU knlYpQ7QA2rDEKs+YWqUstr4pDtHzwQ6mo0rqP+zzsFNBGcrpvIBEADGYTFkNVttZkt6e7yA LNkv3Q39zQCt8qe7qkPdlj3CqygVXfw+h7GlcT9fuc4kd7YxFys4/Wd9icj9ZatGMwffONmi LnUotIq2N7+xvc4Xu76wv+QJpiuGEfCDB+VdZOmOzUPlmMkcJc/EDSH4qGogIYRu72uweKEq VfBI43PZIGpGJ7TjS3THX5WVI2YNSmuwqxnQF/iVqDtD2N72ObkBwIf9GnrOgxEyJ/SQq2R0 g7hd6IYk7SOKt1a8ZGCN6hXXKzmM6gHRC8fyWeTqJcK4BKSdX8PzEuYmAJjSfx4w6DoxdK5/ 9sVrNzaVgDHS0ThH/5kNkZ65KNR7K2nk45LT5Crjbg7w5/kKDY6/XiXDx7v/BOR/a+Ryo+lM MffN3XSnAex8cmIhNINl5Z8CAvDLUtItLcbDOv7hdXt6DSyb65CdyY8JwOt6CWno1tdjyDEG 5ANwVPYY878IFkOJLRTJuUd5ltybaSWjKIwjYJfIXuoyzE7OL63856MC/Os8PcLfY7vYY2LB cvKH1qOcs+an86DWX17+dkcKD/YLrpzwvRMur5+kTgVfXcC0TAl39N4YtaCKM/3ugAaVS1Mw MrbyGnGqVMqlCpjnpYREzapSk8XxbO2kYRsZQd8J9ei98OSqgPf8xM7NCULd/xaZLJUydql1 JdSREId2C15jut21aQARAQABwsF2BBgBCgAgFiEEO5YHwQksFRkI+NPdJGddkSfKF+wFAmcr pvICGwwACgkQJGddkSfKF+xuuxAA4F9iQc61wvAOAidktv4Rztn4QKy8TAyGN3M8zYf/A5Zx VcGgX4J4MhRUoPQNrzmVlrrtE2KILHxQZx5eQyPgixPXri42oG5ePEXZoLU5GFRYSPjjTYmP ypyTPN7uoWLfw4TxJqWCGRLsjnkwvyN3R4161Dty4Uhzqp1IkNhl3ifTDYEvbnmHaNvlvvna 7+9jjEBDEFYDMuO/CA8UtoVQXjy5gtOhZZkEsptfwQYc+E9U99yxGofDul7xH41VdXGpIhUj 4wjd3IbgaCiHxxj/M9eM99ybu5asvHyMo3EFPkyWxZsBlUN/riFXGspG4sT0cwOUhG2ZnExv XXhOGKs/y3VGhjZeCDWZ+0ZQHPCL3HUebLxW49wwLxvXU6sLNfYnTJxdqn58Aq4sBXW5Un0Q vfbd9VFV/bKFfvUscYk2UKPi9vgn1hY38IfmsnoS8b0uwDq75IBvup9pYFyNyPf5SutxhFfP JDjakbdjBoYDWVoaPbp5KAQ2VQRiR54lir/inyqGX+dwzPX/F4OHfB5RTiAFLJliCxniKFsM d8eHe88jWjm6/ilx4IlLl9/MdVUGjLpBi18X7ejLz3U2quYD8DBAGzCjy49wJ4Di4qQjblb2 pTXoEyM2L6E604NbDu0VDvHg7EXh1WwmijEu28c/hEB6DwtzslLpBSsJV0s1/jE= In-Reply-To: <20251124230917.7wxvux5s6j6f5tuz@desk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/25/25 01:09, Pawan Gupta wrote: > On Fri, Nov 21, 2025 at 04:27:05PM +0200, Nikolay Borisov wrote: >> >> >> On 11/20/25 08:19, Pawan Gupta wrote: >>> This ensures that all mitigation modes are explicitly handled, while >>> keeping the mitigation selection for each mode together. This also prepares >>> for adding BHB-clearing mitigation mode for VMSCAPE. >>> >>> Signed-off-by: Pawan Gupta >>> --- >>> arch/x86/kernel/cpu/bugs.c | 22 ++++++++++++++++++---- >>> 1 file changed, 18 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c >>> index 1e9b11198db0fe2483bd17b1327bcfd44a2c1dbf..233594ede19bf971c999f4d3cc0f6f213002c16c 100644 >>> --- a/arch/x86/kernel/cpu/bugs.c >>> +++ b/arch/x86/kernel/cpu/bugs.c >>> @@ -3231,17 +3231,31 @@ early_param("vmscape", vmscape_parse_cmdline); >>> static void __init vmscape_select_mitigation(void) >>> { >>> - if (!boot_cpu_has_bug(X86_BUG_VMSCAPE) || >>> - !boot_cpu_has(X86_FEATURE_IBPB)) { >>> + if (!boot_cpu_has_bug(X86_BUG_VMSCAPE)) { >>> vmscape_mitigation = VMSCAPE_MITIGATION_NONE; >>> return; >>> } >>> - if (vmscape_mitigation == VMSCAPE_MITIGATION_AUTO) { >>> - if (should_mitigate_vuln(X86_BUG_VMSCAPE)) >>> + if ((vmscape_mitigation == VMSCAPE_MITIGATION_AUTO) && >>> + !should_mitigate_vuln(X86_BUG_VMSCAPE)) >>> + vmscape_mitigation = VMSCAPE_MITIGATION_NONE; >>> + >>> + switch (vmscape_mitigation) { >>> + case VMSCAPE_MITIGATION_NONE: >>> + break; >>> + >>> + case VMSCAPE_MITIGATION_IBPB_ON_VMEXIT: >>> + case VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER: >>> + if (!boot_cpu_has(X86_FEATURE_IBPB)) >>> + vmscape_mitigation = VMSCAPE_MITIGATION_NONE; >>> + break; >>> + >>> + case VMSCAPE_MITIGATION_AUTO: >>> + if (boot_cpu_has(X86_FEATURE_IBPB)) >>> vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER; >> >> >> IMO this patch is a net-negative because as per my reply to patch 9 you have >> effectively a dead branch: >> >> The clear BHB_CLEAR_USER one, however it turns out you have yet another one: >> VMSCAPE_MITIGATION_IBPB_ON_VMEXIT as it's only ever set in >> vmscape_update_mitigation() which executes after '_select()' as well and > > Removed VMSCAPE_MITIGATION_IBPB_ON_VMEXIT. > >> additionally you duplicate the FEATURE_IBPB check. > > FEATURE_IBPB check is still needed for VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER. > I don't think we can drop that. But if X86_FEATURE_IBPB is not present then all branches boil down to setting the mitigation to NONE. What I was suggesting is to not remove the that check at the top. > >> So I think either dropping it or removing the superfluous branches is in >> order. >> >>> else >>> vmscape_mitigation = VMSCAPE_MITIGATION_NONE; >>> + break; >>> } >>> } >>> >>