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X-IronPort-AV: E=McAfee;i="6600,9927,10739"; a="356966631" X-IronPort-AV: E=Sophos;i="6.00,236,1681196400"; d="scan'208";a="356966631" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jun 2023 08:39:25 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10739"; a="714434993" X-IronPort-AV: E=Sophos;i="6.00,236,1681196400"; d="scan'208";a="714434993" Received: from spmantha-mobl1.amr.corp.intel.com (HELO [10.209.43.2]) ([10.209.43.2]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jun 2023 08:39:23 -0700 Message-ID: <696ea7fe-3294-f21b-3bc0-3f8cc0a718e9@intel.com> Date: Mon, 12 Jun 2023 08:39:23 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH RFC v9 08/51] 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, dgilbert@redhat.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, liam.merwick@oracle.com, zhi.a.wang@intel.com, Kim Phillips References: <20230612042559.375660-1-michael.roth@amd.com> <20230612042559.375660-9-michael.roth@amd.com> From: Dave Hansen In-Reply-To: <20230612042559.375660-9-michael.roth@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 24A57140024 X-Stat-Signature: 158ib58h6q6wfw4dqhsfpnzei18seqk6 X-HE-Tag: 1686584367-321479 X-HE-Meta: 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 1Zd8kdv5 KN8H35z6eYACHh7iixIqQIdaKCL8m98t0bAGHcpM4Dpeio8qPl/vunQ4g8Dm/v/L2AylVDL8Ki+ejfbLQ2FOJWtFsXCbedd2yQa990vFk2utHGxGlsFLCx2uO4jFB/A741ML377iLiY19nYxspYzeHEveQNh8KvaWToD/R2Gu6kXhid34ZiLr5FWJCC153baTXwaL 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: On 6/11/23 21:25, Michael Roth wrote: > A hardware limitation prevents the host from enabling Automatic IBRS > when SNP is enabled. Instead, fall back to retpolines. "Hardware limitation"? As in, it is a documented, architectural restriction? Or, it's a CPU bug? > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > index f9d060e71c3e..3fba3623ff64 100644 > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -1507,7 +1507,12 @@ static void __init spectre_v2_select_mitigation(void) > > if (spectre_v2_in_ibrs_mode(mode)) { > if (boot_cpu_has(X86_FEATURE_AUTOIBRS)) { > - msr_set_bit(MSR_EFER, _EFER_AUTOIBRS); > + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP)) { > + msr_set_bit(MSR_EFER, _EFER_AUTOIBRS); > + } else { > + pr_err("SNP feature available, not enabling AutoIBRS on the host.\n"); > + mode = spectre_v2_select_retpoline(); > + } I think this would be nicer if you did something like: if (cpu_feature_enabled(X86_FEATURE_SEV_SNP)) setup_clear_cpu_cap(X86_FEATURE_AUTOIBRS); somewhere _else_ in the code instead of smack-dab in the middle of the mitigation selection.