From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 32B2BC433E0 for ; Fri, 5 Jun 2020 19:26:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 160B5206A2 for ; Fri, 5 Jun 2020 19:26:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728063AbgFET0J (ORCPT ); Fri, 5 Jun 2020 15:26:09 -0400 Received: from mga03.intel.com ([134.134.136.65]:18768 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726963AbgFET0I (ORCPT ); Fri, 5 Jun 2020 15:26:08 -0400 IronPort-SDR: n3I0NnNI4r1LG2DD5PeoMLoXXrZssg+o73LbOn/XqoUXeGqMbpiFaT5j6DCGPPiy3UsCLAZErb 9vob7FAtucSg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jun 2020 12:26:07 -0700 IronPort-SDR: N8mvhEuF9Yca0EaUBhaf8fWySQ/j2CY/8kTmbLZhcDGBSiIsoZYSuPht8u0/Gm0igCQOpET3+p L2ywfryHylKg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,477,1583222400"; d="scan'208";a="313279638" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.152]) by FMSMGA003.fm.intel.com with ESMTP; 05 Jun 2020 12:26:07 -0700 From: Sean Christopherson To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org Cc: "H. Peter Anvin" , linux-kernel@vger.kernel.org, Xiaoyao Li , Paolo Bonzini , kvm@vger.kernel.org, Sean Christopherson Subject: [PATCH] x86/split_lock: Don't write MSR_TEST_CTRL on CPUs that aren't whitelisted Date: Fri, 5 Jun 2020 12:26:05 -0700 Message-Id: <20200605192605.7439-1-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.26.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Choo! Choo! All aboard the Split Lock Express, with direct service to Wreckage! Skip split_lock_verify_msr() if the CPU isn't whitelisted as a possible SLD-enabled CPU model to avoid writing MSR_TEST_CTRL. MSR_TEST_CTRL exists, and is writable, on many generations of CPUs. Writing the MSR, even with '0', can result in bizarre, undocumented behavior. This fixes a crash on Haswell when resuming from suspend with a live KVM guest. Because APs use the standard SMP boot flow for resume, they will go through split_lock_init() and the subsequent RDMSR/WRMSR sequence, which runs even when sld_state==sld_off to ensure SLD is disabled. On Haswell (at least, my Haswell), writing MSR_TEST_CTRL with '0' will succeed and _may_ take the SMT _sibling_ out of VMX root mode. When KVM has an active guest, KVM performs VMXON as part of CPU onlining (see kvm_starting_cpu()). Because SMP boot is serialized, the resulting flow is effectively: on_each_ap_cpu() { WRMSR(MSR_TEST_CTRL, 0) VMXON } As a result, the WRMSR can disable VMX on a different CPU that has already done VMXON. This ultimately results in a #UD on VMPTRLD when KVM regains control and attempt run its vCPUs. The above voodoo was confirmed by reworking KVM's VMXON flow to write MSR_TEST_CTRL prior to VMXON, and to serialize the sequence as above. Further verification of the insanity was done by redoing VMXON on all APs after the initial WRMSR->VMXON sequence. The additional VMXON, which should VM-Fail, occasionally succeeded, and also eliminated the unexpected #UD on VMPTRLD. The damage done by writing MSR_TEST_CTRL doesn't appear to be limited to VMX, e.g. after suspend with an active KVM guest, subsequent reboots almost always hang (even when fudging VMXON), a #UD on a random Jcc was observed, suspend/resume stability is qualitatively poor, and so on and so forth. kernel BUG at arch/x86/kvm/x86.c:386! invalid opcode: 0000 [#7] SMP CPU: 1 PID: 2592 Comm: CPU 6/KVM Tainted: G D Hardware name: ASUS Q87M-E/Q87M-E, BIOS 1102 03/03/2014 RIP: 0010:kvm_spurious_fault+0xf/0x20 Code: <0f> 0b 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 RSP: 0018:ffffc0bcc1677b78 EFLAGS: 00010246 RAX: 0000617640000000 RBX: ffff9e8d01d80000 RCX: ffff9e8d4fa40000 RDX: ffff9e8d03360000 RSI: 00000003c3360000 RDI: ffff9e8d03360000 RBP: 0000000000000001 R08: ffff9e8d046d9d40 R09: 0000000000000018 R10: ffffc0bcc1677b80 R11: 0000000000000008 R12: 0000000000000006 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 00007fe16c9f9700(0000) GS:ffff9e8d4fa40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000d7a418 CR3: 00000003c47b1006 CR4: 00000000001626e0 Call Trace: vmx_vcpu_load_vmcs+0x1fb/0x2b0 vmx_vcpu_load+0x3e/0x160 kvm_arch_vcpu_load+0x48/0x260 finish_task_switch+0x140/0x260 __schedule+0x460/0x720 _cond_resched+0x2d/0x40 kvm_arch_vcpu_ioctl_run+0x82e/0x1ca0 kvm_vcpu_ioctl+0x363/0x5c0 ksys_ioctl+0x88/0xa0 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x4c/0x170 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Cc: Thomas Gleixner Cc: Xiaoyao Li Cc: Paolo Bonzini Cc: kvm@vger.kernel.org Fixes: dbaba47085b0c ("x86/split_lock: Rework the initialization flow of split lock detection") Signed-off-by: Sean Christopherson --- arch/x86/kernel/cpu/intel.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index a19a680542ce..19b6c42739fc 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -48,6 +48,13 @@ enum split_lock_detect_state { static enum split_lock_detect_state sld_state __ro_after_init = sld_off; static u64 msr_test_ctrl_cache __ro_after_init; +/* + * With a name like MSR_TEST_CTL it should go without saying, but don't touch + * MSR_TEST_CTL unless the CPU is one of the whitelisted models. Writing it + * on CPUs that do not support SLD can cause fireworks, even when writing '0'. + */ +static bool cpu_model_supports_sld __ro_after_init; + /* * Processors which have self-snooping capability can handle conflicting * memory type across CPUs by snooping its own cache. However, there exists @@ -1064,7 +1071,8 @@ static void sld_update_msr(bool on) static void split_lock_init(void) { - split_lock_verify_msr(sld_state != sld_off); + if (cpu_model_supports_sld) + split_lock_verify_msr(sld_state != sld_off); } static void split_lock_warn(unsigned long ip) @@ -1167,5 +1175,6 @@ void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) return; } + cpu_model_supports_sld = true; split_lock_setup(); } -- 2.26.0