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X-IronPort-AV: E=McAfee;i="6600,9927,10876"; a="387667406" X-IronPort-AV: E=Sophos;i="6.03,257,1694761200"; d="scan'208";a="387667406" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Oct 2023 14:50:43 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10876"; a="903394108" X-IronPort-AV: E=Sophos;i="6.03,257,1694761200"; d="scan'208";a="903394108" Received: from hannahwo-mobl1.amr.corp.intel.com (HELO [10.209.35.60]) ([10.209.35.60]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Oct 2023 14:48:12 -0700 Message-ID: <9fe968f0-cf38-4abf-b01c-5591c97ec886@intel.com> Date: Fri, 27 Oct 2023 14:50:41 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 05/50] x86/speculation: Do not enable Automatic IBRS if SEV SNP is enabled Content-Language: en-US To: Michael Roth , kvm@vger.kernel.org Cc: linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org, pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com, bp@alien8.de, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, pankaj.gupta@amd.com, liam.merwick@oracle.com, zhi.a.wang@intel.com, Kim Phillips References: <20231016132819.1002933-1-michael.roth@amd.com> <20231016132819.1002933-6-michael.roth@amd.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 99966140023 X-Stat-Signature: jcigeyxj8zkkhzg7rzo1s59nk4jbamha X-HE-Tag: 1698443445-921165 X-HE-Meta: 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 ClL3Vzt6 7m+HOQ1AC39+huk61EoyDDp2bI8rHD/TZD7Puz9OEPI3kB/oAZSyGaEE/+TU8fdtoMiccCvz4Z0iOQ9+wdVES5c8JGLvFVBEUQOcosWVb0x7uLBV1wxNtBs12kUbkdnUXzeP/+1LTksNL6ltveOKeoKSpyBhaFuiTTz+de23Sl1orXLV7Fwnk/Q73lpZO52Nr3ggocrKP9XAy4nbbPGsLfTMR3GGbuHYDx4QokeQuIZ2doEY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/16/23 06:27, Michael Roth wrote: > Without SEV-SNP, Automatic IBRS protects only the kernel. But when > SEV-SNP is enabled, the Automatic IBRS protection umbrella widens to all > host-side code, including userspace. This protection comes at a cost: > reduced userspace indirect branch performance. > > To avoid this performance loss, don't use Automatic IBRS on SEV-SNP > hosts. Fall back to retpolines instead. Thanks for the updated changelog: Acked-by: Dave Hansen BTW, have you given your hardware folks a hard time about this? It seems _kinda_ silly to be using retpolines when the hardware has a perfectly good IBRS implementation for the kernel. Just please make sure there's a good underlying reason for this behavior and as opposed to being some kind of inadvertent side effect. I assume Auto-IBRS and SEV-SNP are going to be with us for a long time, so it would be nice to have a long term solution here.