From nobody Mon Sep 29 21:09:36 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0AA3AC00140 for ; Tue, 16 Aug 2022 01:03:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233136AbiHPBDU (ORCPT ); Mon, 15 Aug 2022 21:03:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54572 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347961AbiHPA52 (ORCPT ); Mon, 15 Aug 2022 20:57:28 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3D0F7DAED6; Mon, 15 Aug 2022 13:48:50 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id CF703B811AB; Mon, 15 Aug 2022 20:48:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 14836C433C1; Mon, 15 Aug 2022 20:48:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1660596528; bh=aPB0rUdcfekjqm3H0m8FGPbGicTahUmBH0WeHRYV5hs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Kglx+VVoS2FZ89V7eCegIMSavA0V+0ab6lPMszVkFPT/+y+l+xNTLSqQob1Jt5aSG xLxW/XmOPxJJ12KK116FEYEfO3GMiGl/KTetIMAGyGPikmat8+Hfjz424RnErkMw4y L3RD28ojm6/p1eCvlkO9sHU1ASn9Tl56RLbDNWhA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Sean Christopherson , Paolo Bonzini , Sasha Levin Subject: [PATCH 5.19 1108/1157] KVM: nVMX: Attempt to load PERF_GLOBAL_CTRL on nVMX xfer iff it exists Date: Mon, 15 Aug 2022 20:07:44 +0200 Message-Id: <20220815180524.609692721@linuxfoundation.org> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220815180439.416659447@linuxfoundation.org> References: <20220815180439.416659447@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Sean Christopherson [ Upstream commit 4496a6f9b45e8cd83343ad86a3984d614e22cf54 ] Attempt to load PERF_GLOBAL_CTRL during nested VM-Enter/VM-Exit if and only if the MSR exists (according to the guest vCPU model). KVM has very misguided handling of VM_{ENTRY,EXIT}_LOAD_IA32_PERF_GLOBAL_CTRL and attempts to force the nVMX MSR settings to match the vPMU model, i.e. to hide/expose the control based on whether or not the MSR exists from the guest's perspective. KVM's modifications fail to handle the scenario where the vPMU is hidden from the guest _after_ being exposed to the guest, e.g. by userspace doing multiple KVM_SET_CPUID2 calls, which is allowed if done before any KVM_RUN. nested_vmx_pmu_refresh() is called if and only if there's a recognized vPMU, i.e. KVM will leave the bits in the allow state and then ultimately reject the MSR load and WARN. KVM should not force the VMX MSRs in the first place. KVM taking control of the MSRs was a misguided attempt at mimicking what commit 5f76f6f5ff96 ("KVM: nVMX: Do not expose MPX VMX controls when guest MPX disabled", 2018-10-01) did for MPX. However, the MPX commit was a workaround for another KVM bug and not something that should be imitated (and it should never been done in the first place). In other words, KVM's ABI _should_ be that userspace has full control over the MSRs, at which point triggering the WARN that loading the MSR must not fail is trivial. The intent of the WARN is still valid; KVM has consistency checks to ensure that vmcs12->{guest,host}_ia32_perf_global_ctrl is valid. The problem is that '0' must be considered a valid value at all times, and so the simple/obvious solution is to just not actually load the MSR when it does not exist. It is userspace's responsibility to provide a sane vCPU model, i.e. KVM is well within its ABI and Intel's VMX architecture to skip the loads if the MSR does not exist. Fixes: 03a8871add95 ("KVM: nVMX: Expose load IA32_PERF_GLOBAL_CTRL VM-{Entr= y,Exit} control") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-Id: <20220722224409.1336532-5-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin --- arch/x86/kvm/vmx/nested.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 66735fbb791d..ef21c5fe172e 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -2617,6 +2617,7 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, stru= ct vmcs12 *vmcs12, } =20 if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL) && + intel_pmu_has_perf_global_ctrl(vcpu_to_pmu(vcpu)) && WARN_ON_ONCE(kvm_set_msr(vcpu, MSR_CORE_PERF_GLOBAL_CTRL, vmcs12->guest_ia32_perf_global_ctrl))) { *entry_failure_code =3D ENTRY_FAIL_DEFAULT; @@ -4342,7 +4343,8 @@ static void load_vmcs12_host_state(struct kvm_vcpu *v= cpu, vmcs_write64(GUEST_IA32_PAT, vmcs12->host_ia32_pat); vcpu->arch.pat =3D vmcs12->host_ia32_pat; } - if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL) + if ((vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL) && + intel_pmu_has_perf_global_ctrl(vcpu_to_pmu(vcpu))) WARN_ON_ONCE(kvm_set_msr(vcpu, MSR_CORE_PERF_GLOBAL_CTRL, vmcs12->host_ia32_perf_global_ctrl)); =20 --=20 2.35.1