From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f48.google.com (mail-wr1-f48.google.com [209.85.221.48]) (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 81CA02FF151 for ; Fri, 21 Nov 2025 14:18:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.48 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763734700; cv=none; b=BkgoV2paQm3oIX67rLOetwDYc30xrR6hqsCRDfPjizaTWERJPSW3s0+YvVGpzJqteFpPb2BuugcxL+cj+L7uKbfrGz9U/X1OYgQYRMtwefFE3USYP+uHq3CptjUilLDwGI4b4MYo2HgD+prfLaYsx+rx1696dlXnUbfQb5vqtB8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763734700; c=relaxed/simple; bh=YxWWlAsZqYAxuYhnWljtUxq/fF/WET+4jUiU+3A7jKg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fNqLH4K1/A+YSD/oA9xXus55NNouAf4xYP8DKQN53QjZMtG7Dec4p3RS4PwfUtm0moK6OCFGb6VZdzfM64wgc9GB/LqG57apGIVkDvC6asx4zVhNmmEQx7WaPjs1gmrNKDEDLolqzcYSlASumX47UAIUZEtHejN/ihO5En6K5kU= 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=JVBgbQXy; arc=none smtp.client-ip=209.85.221.48 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="JVBgbQXy" Received: by mail-wr1-f48.google.com with SMTP id ffacd0b85a97d-42b3c965cc4so1118577f8f.0 for ; Fri, 21 Nov 2025 06:18:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1763734697; x=1764339497; 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=503K01X0EjRdBqgywH22/w+iIk3UaBmqSzYIZrwCI8c=; b=JVBgbQXy2kjwN26nhVZ8+G7q8RghvbEAfl5caYBIKvR+aOaT2q9KX5mzF2xR8pLGkc niLaYSwJAJ4KGnlsxlL5qXQM0BO3lVeUorXz8dnWoh6bGx1/+Fb2njtklxIekA2ZO1bG 0fZNInamWDQw3WKoq6s7Dh2v1XqLlohvUrJAxUqI1NMzofzd5yyW9fBcddLhuCY4ECVd OpprLgh2PV4mAEKBUzkUdoGkINBRGdhYb5WEU/kang8NEnNxbIY0tVD29WtE3WzyEgh1 VJGQCs5q9oDvL39/my48OVtxW1wlcuFP8x9UdY0zBgDKQCbE1mSK4CJT2szq9EtITrfD 57ZQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1763734697; x=1764339497; 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=503K01X0EjRdBqgywH22/w+iIk3UaBmqSzYIZrwCI8c=; b=tJ2tPYDmqPUus5L2LlZ1KIttKB36LjZsucMaMzbT8PXhj4GIPShvGvP+1tmFJLG+sQ 8cXz2kl52dWwJ+/0NuzLIAk4lKZ20pCdlDvT99zG3hhMruKHV4TO0qe1gzDtvOQX5I/m eny9VL4uyPrBU+R+zFQjRueKMkJvphQF6kEj8MRmklS3ZqsmIkwHVTyrv/lddDj3WMET zlkD1XOFHut/HCXut/6WVb18MHlZ+OJvPeOY++Zbvm4AVoIFRLhBA2VKjEPOiv0nPtx9 rA2rg6MnWNHzPvm0xrxd1cTQ3l+rTQko01zi8O5lzStemV9mx3fFvOivMFXX78ci98tX GQKg== X-Forwarded-Encrypted: i=1; AJvYcCW6owb1AgSubujOleMFp8vgLjlM+zyy5xeat3of39fJ5PQXMgD2x4i7KeovVgCuBQ9vBuk=@vger.kernel.org X-Gm-Message-State: AOJu0YxLpJczeD/v1WKKON8r8IogshTUO1tyJQX2tifS2oY4LFiKIdiq Ko7QCnKaCDsdGYzdBAvCtjivMykyR2COkijh7OWhBqEJPKDPCsuwqrfPDFQWhzb3Kwc= X-Gm-Gg: ASbGncsrW5bpiN3tFRjRMJOmelBpFOB2NY8VRWBgxMweGZkq+KKivwOn5o5fDkWiFAd YG9L0Mj5kjVrPZPCxmEV/yNkzEs+oLDfsgrKy88x2/CwIqvcn4hvXFZHnOGJ9FDl7Mwtq0aWyjI me0cW389ZQLbkLHxYTmMJD8xdtJu9ON54O3UGwrfcNoqWZxR/kKVWCyBPnYujdqh9+V1KvDRyiM l3ovsH56Yuq+qtl6Jjz3LGIpaqxf/TkuZInk/pEw/S4atDpJVw3id2ult0KdZZ2Lq4aDMGHAavj iPwG0LyBbqHl2zVdAZiBl99ewnT5kLkTO19pm5kMUKb4Z6Vu7Rh30gycMr482f4WGEBg2VMYPDl 0mc3O8QEf+KJDmapob389B7zePhE1MsB4fcJ6SCziGzOIG4zhq/xPZsyZEdiQYkHepb5GHsmiAh xljG44M2hVpf0mkf8PyoDwuDLui3biuAEy5Eay X-Google-Smtp-Source: AGHT+IGNB82e/U2NCkMNUaSlyJGpUrw+Ly8FAinwRhyZzIKg4Ey937ANGlL06E27249r5LNmnn/Q7Q== X-Received: by 2002:a05:6000:4305:b0:429:ef72:c33a with SMTP id ffacd0b85a97d-42cba63b5e9mr7259439f8f.3.1763734696702; Fri, 21 Nov 2025 06:18:16 -0800 (PST) Received: from [192.168.0.20] (nborisov.ddns.nbis.net. [85.187.216.236]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8846e446463sm39013966d6.11.2025.11.21.06.18.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Nov 2025 06:18:15 -0800 (PST) Message-ID: <67b9ad70-71ed-44ee-bc45-e02eb75043d2@suse.com> Date: Fri, 21 Nov 2025 16:18:09 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 09/11] x86/vmscape: Deploy BHB clearing mitigation To: Pawan Gupta , x86@kernel.org, David Kaplan , "H. Peter Anvin" , Josh Poimboeuf , Sean Christopherson , Paolo Bonzini , Borislav Petkov , Dave Hansen Cc: 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-v4-9-1adad4e69ddc@linux.intel.com> 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: <20251119-vmscape-bhb-v4-9-1adad4e69ddc@linux.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/20/25 08:19, Pawan Gupta wrote: > IBPB mitigation for VMSCAPE is an overkill on CPUs that are only affected > by the BHI variant of VMSCAPE. On such CPUs, eIBRS already provides > indirect branch isolation between guest and host userspace. However, branch > history from guest may also influence the indirect branches in host > userspace. > > To mitigate the BHI aspect, use clear_bhb_loop(). > > Signed-off-by: Pawan Gupta > @@ -3278,6 +3290,9 @@ static void __init vmscape_apply_mitigation(void) > { > if (vmscape_mitigation == VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER) > static_call_update(vmscape_predictor_flush, write_ibpb); > + else if (vmscape_mitigation == VMSCAPE_MITIGATION_BHB_CLEAR_EXIT_TO_USER && > + IS_ENABLED(CONFIG_X86_64)) why the x86_64 dependency ? > + static_call_update(vmscape_predictor_flush, clear_bhb_loop); > } > > #undef pr_fmt > @@ -3369,6 +3384,7 @@ void cpu_bugs_smt_update(void) > break; > case VMSCAPE_MITIGATION_IBPB_ON_VMEXIT: > case VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER: > + case VMSCAPE_MITIGATION_BHB_CLEAR_EXIT_TO_USER: > /* > * Hypervisors can be attacked across-threads, warn for SMT when > * STIBP is not already enabled system-wide. >