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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 2CE22C433ED for ; Mon, 10 May 2021 08:26:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07D066144F for ; Mon, 10 May 2021 08:26:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230181AbhEJI1W (ORCPT ); Mon, 10 May 2021 04:27:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:46081 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230135AbhEJI0p (ORCPT ); Mon, 10 May 2021 04:26:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620635136; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VP7OxY1nqNC6hZWU/TAr2hXHHO1myebSqQjjAkILYGY=; b=TOduMg2gmnobhdb1JSik5neeYOTqqFSrZg1LDBOLf7v9bL+ysgZuaHNigGrl2OS0kwo+/J oxBGOu151C6RCMEB7k7adDmbzFljgm2oomCV75p4DJyFM0OoM9583YqKvFuAPBEIJ5BLXL 2PI93gRzqi5G9DQ9eeFduCxdEYuhd7k= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-594-SOd-Msz5NjuRgJ4FjbR4QA-1; Mon, 10 May 2021 04:25:34 -0400 X-MC-Unique: SOd-Msz5NjuRgJ4FjbR4QA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 494991008060; Mon, 10 May 2021 08:25:33 +0000 (UTC) Received: from starship (unknown [10.40.194.86]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1A89C60E3A; Mon, 10 May 2021 08:25:29 +0000 (UTC) Message-ID: Subject: Re: [PATCH 09/15] KVM: VMX: Use flag to indicate "active" uret MSRs instead of sorting list From: Maxim Levitsky To: Sean Christopherson , Paolo Bonzini Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Xiaoyao Li , Reiji Watanabe Date: Mon, 10 May 2021 11:25:28 +0300 In-Reply-To: <20210504171734.1434054-10-seanjc@google.com> References: <20210504171734.1434054-1-seanjc@google.com> <20210504171734.1434054-10-seanjc@google.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2021-05-04 at 10:17 -0700, Sean Christopherson wrote: > Explicitly flag a uret MSR as needing to be loaded into hardware instead of > resorting the list of "active" MSRs and tracking how many MSRs in total > need to be loaded. The only benefit to sorting the list is that the loop > to load MSRs during vmx_prepare_switch_to_guest() doesn't need to iterate > over all supported uret MRS, only those that are active. But that is a > pointless optimization, as the most common case, running a 64-bit guest, > will load the vast majority of MSRs. Not to mention that a single WRMSR is > far more expensive than iterating over the list. > > Providing a stable list order obviates the need to track a given MSR's > "slot" in the per-CPU list of user return MSRs; all lists simply use the > same ordering. Future patches will take advantage of the stable order to > further simplify the related code. > > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/vmx/vmx.c | 80 ++++++++++++++++++++++-------------------- > arch/x86/kvm/vmx/vmx.h | 2 +- > 2 files changed, 42 insertions(+), 40 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 68454b0de2b1..6caabcd5037e 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -458,8 +458,9 @@ static unsigned long host_idt_base; > * Though SYSCALL is only supported in 64-bit mode on Intel CPUs, kvm > * will emulate SYSCALL in legacy mode if the vendor string in guest > * CPUID.0:{EBX,ECX,EDX} is "AuthenticAMD" or "AMDisbetter!" To > - * support this emulation, IA32_STAR must always be included in > - * vmx_uret_msrs_list[], even in i386 builds. > + * support this emulation, MSR_STAR is included in the list for i386, > + * but is never loaded into hardware. MSR_CSTAR is also never loaded > + * into hardware and is here purely for emulation purposes. > */ > static u32 vmx_uret_msrs_list[] = { > #ifdef CONFIG_X86_64 > @@ -702,18 +703,12 @@ static bool is_valid_passthrough_msr(u32 msr) > return r; > } > > -static inline int __vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr) > +static inline int __vmx_find_uret_msr(u32 msr) > { > int i; > > - /* > - * Note, vmx->guest_uret_msrs is the same size as vmx_uret_msrs_list, > - * but is ordered differently. The MSR is matched against the list of > - * supported uret MSRs using "slot", but the index that is returned is > - * the index into guest_uret_msrs. > - */ > for (i = 0; i < vmx_nr_uret_msrs; ++i) { > - if (vmx_uret_msrs_list[vmx->guest_uret_msrs[i].slot] == msr) > + if (vmx_uret_msrs_list[i] == msr) > return i; > } > return -1; > @@ -723,7 +718,7 @@ struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr) > { > int i; > > - i = __vmx_find_uret_msr(vmx, msr); > + i = __vmx_find_uret_msr(msr); > if (i >= 0) > return &vmx->guest_uret_msrs[i]; > return NULL; > @@ -732,13 +727,14 @@ struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr) > static int vmx_set_guest_uret_msr(struct vcpu_vmx *vmx, > struct vmx_uret_msr *msr, u64 data) > { > + unsigned int slot = msr - vmx->guest_uret_msrs; > int ret = 0; > > u64 old_msr_data = msr->data; > msr->data = data; > - if (msr - vmx->guest_uret_msrs < vmx->nr_active_uret_msrs) { > + if (msr->load_into_hardware) { > preempt_disable(); > - ret = kvm_set_user_return_msr(msr->slot, msr->data, msr->mask); > + ret = kvm_set_user_return_msr(slot, msr->data, msr->mask); > preempt_enable(); > if (ret) > msr->data = old_msr_data; > @@ -1090,7 +1086,7 @@ static bool update_transition_efer(struct vcpu_vmx *vmx) > return false; > } > > - i = __vmx_find_uret_msr(vmx, MSR_EFER); > + i = __vmx_find_uret_msr(MSR_EFER); > if (i < 0) > return false; > > @@ -1252,11 +1248,14 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) > */ > if (!vmx->guest_uret_msrs_loaded) { > vmx->guest_uret_msrs_loaded = true; > - for (i = 0; i < vmx->nr_active_uret_msrs; ++i) > - kvm_set_user_return_msr(vmx->guest_uret_msrs[i].slot, > + for (i = 0; i < vmx_nr_uret_msrs; ++i) { > + if (!vmx->guest_uret_msrs[i].load_into_hardware) > + continue; > + > + kvm_set_user_return_msr(i, > vmx->guest_uret_msrs[i].data, > vmx->guest_uret_msrs[i].mask); > - > + } > } > > if (vmx->nested.need_vmcs12_to_shadow_sync) > @@ -1763,19 +1762,16 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu) > vmx_clear_hlt(vcpu); > } > > -static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr) > +static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr, > + bool load_into_hardware) > { > - struct vmx_uret_msr tmp; > - int from, to; > + struct vmx_uret_msr *uret_msr; > > - from = __vmx_find_uret_msr(vmx, msr); > - if (from < 0) > + uret_msr = vmx_find_uret_msr(vmx, msr); > + if (!uret_msr) > return; > - to = vmx->nr_active_uret_msrs++; > > - tmp = vmx->guest_uret_msrs[to]; > - vmx->guest_uret_msrs[to] = vmx->guest_uret_msrs[from]; > - vmx->guest_uret_msrs[from] = tmp; > + uret_msr->load_into_hardware = load_into_hardware; > } > > /* > @@ -1785,30 +1781,36 @@ static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr) > */ > static void setup_msrs(struct vcpu_vmx *vmx) > { > - vmx->guest_uret_msrs_loaded = false; > - vmx->nr_active_uret_msrs = 0; > #ifdef CONFIG_X86_64 > + bool load_syscall_msrs; > + > /* > * The SYSCALL MSRs are only needed on long mode guests, and only > * when EFER.SCE is set. > */ > - if (is_long_mode(&vmx->vcpu) && (vmx->vcpu.arch.efer & EFER_SCE)) { > - vmx_setup_uret_msr(vmx, MSR_STAR); > - vmx_setup_uret_msr(vmx, MSR_LSTAR); > - vmx_setup_uret_msr(vmx, MSR_SYSCALL_MASK); > - } > + load_syscall_msrs = is_long_mode(&vmx->vcpu) && > + (vmx->vcpu.arch.efer & EFER_SCE); > + > + vmx_setup_uret_msr(vmx, MSR_STAR, load_syscall_msrs); > + vmx_setup_uret_msr(vmx, MSR_LSTAR, load_syscall_msrs); > + vmx_setup_uret_msr(vmx, MSR_SYSCALL_MASK, load_syscall_msrs); > #endif > - if (update_transition_efer(vmx)) > - vmx_setup_uret_msr(vmx, MSR_EFER); > + vmx_setup_uret_msr(vmx, MSR_EFER, update_transition_efer(vmx)); > > - if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP) || > - guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDPID)) > - vmx_setup_uret_msr(vmx, MSR_TSC_AUX); > + vmx_setup_uret_msr(vmx, MSR_TSC_AUX, > + guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP) || > + guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDPID)); > > - vmx_setup_uret_msr(vmx, MSR_IA32_TSX_CTRL); > + vmx_setup_uret_msr(vmx, MSR_IA32_TSX_CTRL, true); > > if (cpu_has_vmx_msr_bitmap()) > vmx_update_msr_bitmap(&vmx->vcpu); > + > + /* > + * The set of MSRs to load may have changed, reload MSRs before the > + * next VM-Enter. > + */ > + vmx->guest_uret_msrs_loaded = false; > } > > static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset) > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h > index d71ed8b425c5..16e4e457ba23 100644 > --- a/arch/x86/kvm/vmx/vmx.h > +++ b/arch/x86/kvm/vmx/vmx.h > @@ -36,7 +36,7 @@ struct vmx_msrs { > }; > > struct vmx_uret_msr { > - unsigned int slot; /* The MSR's slot in kvm_user_return_msrs. */ > + bool load_into_hardware; > u64 data; > u64 mask; > }; This is a very welcomed change, the old code was very complicated to understand. However I still feel that it would be nice to have a comment explaining that vmx->guest_uret_msrs follow the same order now as the (eventually common) uret msr list, and basically is a parallel array that extends the percpu 'user_return_msrs' and the global kvm_uret_msrs_list arrays. In fact why not to fold the vmx->guest_uret_msrs into the x86 common uret msr list? There is nothing VMX specific in this list IMHO and SVM can use it as well, in fact it has 'svm->tsc_aux' which is the 'data' field of a 'struct vmx_uret_msr' Reviewed-by: Maxim Levitsky Best regards, Maxim Levitsky