From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.alien8.de (mail.alien8.de [65.109.113.108]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A86C61C683 for ; Wed, 25 Oct 2023 17:34:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=alien8.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=alien8.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (4096-bit key) header.d=alien8.de header.i=@alien8.de header.b="g6VLSRnR" Received: from localhost (localhost.localdomain [127.0.0.1]) by mail.alien8.de (SuperMail on ZX Spectrum 128k) with ESMTP id 05B4C40E00B1; Wed, 25 Oct 2023 17:34:20 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at mail.alien8.de Authentication-Results: mail.alien8.de (amavisd-new); dkim=pass (4096-bit key) header.d=alien8.de Received: from mail.alien8.de ([127.0.0.1]) by localhost (mail.alien8.de [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 7Pf1WCNFuvJb; Wed, 25 Oct 2023 17:34:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=alien8; t=1698255257; bh=cWIDMNOmR3ejJPcU9ueROUfewQ1CyI98mmrkHIjnZ44=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=g6VLSRnRm5zCmwYW7CVRcW/eVYsEK3mhd4c3sl/AfsohA2o2R1IXnFQaZk8uvMonR xUnzHqJaAxFj6ztSQ29uPqXt/mVG0zKrfKKr3+unht/AshxNaXRxKIccmGS3l+8Ckm QEx1rfg9VC7PTlrPV9la72GosU9iwiSVuIG8KwsbAhHLsAtOSRWlO9pPq5NuriOzWu KzIyf/6JQjTe9YgoEt39cyJprQp4aeue5zmmjF3nhG59IjNztQ9xkuxNre/qEKJQrU HsGxkqT2V6+6DFhClTwx/qHV5J1BHDnnItTn4CM5EaY/lPPW1zZYgFMCN/k29KJK3l xKizx5105HyvvpFZ+aq87XaKSH9dvbrWxo3J1CG/YWCAfBr8cF4WwFBheWLW6R91+v fgjtzs77e3LuESXRQnLNSXKSmScZFqNeXvGDTUglNtPLOAzRoeRHEXV5RpveuAKx59 7AwfyjPkdIzBUKBSTC6KkKe9x1ZNgJqRUj6RdSLxYnVItRqoqrpN2CrNx9Hz5KsxFw n1zVRlT8bSixc2z4YX4Ea4utNAqf/RYC3Y27/Ei7NGc6OOXqA7jWXBr1X3IfSrKmoA s6xwu3gstPtxWNXyYcB9b9X9i925IhMy0522+oreqktadtrynCM2YYc4tdtHa+CTtt agJepz0t8AYaGiH8fapHIGKY= Received: from zn.tnic (pd95304da.dip0.t-ipconnect.de [217.83.4.218]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature ECDSA (P-256) server-digest SHA256) (No client certificate requested) by mail.alien8.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id AAE5E40E0199; Wed, 25 Oct 2023 17:33:36 +0000 (UTC) Date: Wed, 25 Oct 2023 19:33:31 +0200 From: Borislav Petkov To: Michael Roth Cc: kvm@vger.kernel.org, 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, 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 Subject: Re: [PATCH v10 05/50] x86/speculation: Do not enable Automatic IBRS if SEV SNP is enabled Message-ID: <20231025173331.GCZTlRa3Tzfc1fHvCu@fat_crate.local> References: <20231016132819.1002933-1-michael.roth@amd.com> <20231016132819.1002933-6-michael.roth@amd.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20231016132819.1002933-6-michael.roth@amd.com> On Mon, Oct 16, 2023 at 08:27:34AM -0500, Michael Roth wrote: > From: Kim Phillips > > 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. > > Signed-off-by: Kim Phillips > [mdr: squash in changes from review discussion] > Signed-off-by: Michael Roth > --- > arch/x86/kernel/cpu/common.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) Acked-by: Borislav Petkov (AMD) -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette