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 C31F4C433FE for ; Fri, 7 Jan 2022 18:56:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233033AbiAGS4I (ORCPT ); Fri, 7 Jan 2022 13:56:08 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:28051 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232853AbiAGSzh (ORCPT ); Fri, 7 Jan 2022 13:55:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1641581737; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ms8oamnV9ATtAzyj0HE2k4dLqAn6UNVYQIiTNYGjoYQ=; b=OjRIMBeKApyMO9RneD94ciRALxSgC0ozcddSnJzJW68szfVHZw0SqwBZuLKhaKp9Vykyfo 3IeCBrpPfOD8aK+9qbXejQhA8s4GU0ullkPghCGCrVub0TrR9pj/fkQEkGpsueRk0Btx8S zE6TSbKkr7dGBraZfguqGut3dmZ7Ba8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-414-9mXsQg6TOd6q09GtKhJZKQ-1; Fri, 07 Jan 2022 13:55:33 -0500 X-MC-Unique: 9mXsQg6TOd6q09GtKhJZKQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7BFAB10168D1; Fri, 7 Jan 2022 18:55:32 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id C26378CB2B; Fri, 7 Jan 2022 18:55:31 +0000 (UTC) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: guang.zeng@intel.com, jing2.liu@intel.com, kevin.tian@intel.com, seanjc@google.com, tglx@linutronix.de, wei.w.wang@intel.com, yang.zhong@intel.com Subject: [PATCH v6 21/21] kvm: x86: Disable interception for IA32_XFD on demand Date: Fri, 7 Jan 2022 13:55:12 -0500 Message-Id: <20220107185512.25321-22-pbonzini@redhat.com> In-Reply-To: <20220107185512.25321-1-pbonzini@redhat.com> References: <20220107185512.25321-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kevin Tian Always intercepting IA32_XFD causes non-negligible overhead when this register is updated frequently in the guest. Disable r/w emulation after intercepting the first WRMSR(IA32_XFD) with a non-zero value. Disable WRMSR emulation implies that IA32_XFD becomes out-of-sync with the software states in fpstate and the per-cpu xfd cache. This leads to two additional changes accordingly: - Call fpu_sync_guest_vmexit_xfd_state() after vm-exit to bring software states back in-sync with the MSR, before handle_exit_irqoff() is called. - Always trap #NM once write interception is disabled for IA32_XFD. The #NM exception is rare if the guest doesn't use dynamic features. Otherwise, there is at most one exception per guest task given a dynamic feature. p.s. We have confirmed that SDM is being revised to say that when setting IA32_XFD[18] the AMX register state is not guaranteed to be preserved. This clarification avoids adding mess for a creative guest which sets IA32_XFD[18]=1 before saving active AMX state to its own storage. Signed-off-by: Kevin Tian Signed-off-by: Jing Liu Signed-off-by: Yang Zhong Message-Id: <20220105123532.12586-22-yang.zhong@intel.com> Signed-off-by: Paolo Bonzini --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/vmx/vmx.c | 24 +++++++++++++++++++----- arch/x86/kvm/vmx/vmx.h | 2 +- arch/x86/kvm/x86.c | 8 ++++++++ 4 files changed, 29 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 6cbf97a2ebc4..89d1fdb39c46 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -647,6 +647,7 @@ struct kvm_vcpu_arch { u64 smi_count; bool tpr_access_reporting; bool xsaves_enabled; + bool xfd_no_write_intercept; u64 ia32_xss; u64 microcode_version; u64 arch_capabilities; diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index b8b7f5c7b3df..15e30602782b 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -162,6 +162,7 @@ static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = { MSR_FS_BASE, MSR_GS_BASE, MSR_KERNEL_GS_BASE, + MSR_IA32_XFD, MSR_IA32_XFD_ERR, #endif MSR_IA32_SYSENTER_CS, @@ -764,10 +765,11 @@ void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu) } /* - * Trap #NM if guest xfd contains a non-zero value so guest XFD_ERR - * can be saved timely. + * Disabling xfd interception indicates that dynamic xfeatures + * might be used in the guest. Always trap #NM in this case + * to save guest xfd_err timely. */ - if (vcpu->arch.guest_fpu.fpstate->xfd) + if (vcpu->arch.xfd_no_write_intercept) eb |= (1u << NM_VECTOR); vmcs_write32(EXCEPTION_BITMAP, eb); @@ -1978,9 +1980,21 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) break; case MSR_IA32_XFD: ret = kvm_set_msr_common(vcpu, msr_info); - /* Update #NM interception according to guest xfd */ - if (!ret) + /* + * Always intercepting WRMSR could incur non-negligible + * overhead given xfd might be changed frequently in + * guest context switch. Disable write interception + * upon the first write with a non-zero value (indicating + * potential usage on dynamic xfeatures). Also update + * exception bitmap to trap #NM for proper virtualization + * of guest xfd_err. + */ + if (!ret && data) { + vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD, + MSR_TYPE_RW); + vcpu->arch.xfd_no_write_intercept = true; vmx_update_exception_bitmap(vcpu); + } break; #endif case MSR_IA32_SYSENTER_CS: diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index 69dd2f85abdc..f8fc7441baea 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -349,7 +349,7 @@ struct vcpu_vmx { struct lbr_desc lbr_desc; /* Save desired MSR intercept (read: pass-through) state */ -#define MAX_POSSIBLE_PASSTHROUGH_MSRS 14 +#define MAX_POSSIBLE_PASSTHROUGH_MSRS 15 struct { DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS); DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index bde18ca657db..60da2331ec32 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10083,6 +10083,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) vcpu->mode = OUTSIDE_GUEST_MODE; smp_wmb(); + /* + * Sync xfd before calling handle_exit_irqoff() which may + * rely on the fact that guest_fpu::xfd is up-to-date (e.g. + * in #NM irqoff handler). + */ + if (vcpu->arch.xfd_no_write_intercept) + fpu_sync_guest_vmexit_xfd_state(); + static_call(kvm_x86_handle_exit_irqoff)(vcpu); if (vcpu->arch.guest_fpu.xfd_err) -- 2.31.1