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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31D15C433FE for ; Fri, 15 Apr 2022 14:02:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354242AbiDOOFH (ORCPT ); Fri, 15 Apr 2022 10:05:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40100 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354233AbiDOOFE (ORCPT ); Fri, 15 Apr 2022 10:05:04 -0400 Received: from mail-ed1-x52b.google.com (mail-ed1-x52b.google.com [IPv6:2a00:1450:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B039DBA306; Fri, 15 Apr 2022 07:02:35 -0700 (PDT) Received: by mail-ed1-x52b.google.com with SMTP id v15so9990069edb.12; Fri, 15 Apr 2022 07:02:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=B4NLxiEMn45fm7ZP4Wwd+hPT7xASfT/B5aQNlTl+H7A=; b=ZiW/IZTB1xy4IkU2FwMIBsjW5AF48i2mw5+IHYG/77iBzkTE5vqG5zni7CYEqfzG9g UMrQSFDdOoFhPt/MUXqcvlT6H1B1HFk3rGNRgmlNZmXl3ovUjAXebcZjBB8BRvyWJ5Sj K53U/szymK7RpOmSw65Hav9uieSfYOs+P+63y+3OLIlQry7tXbploGVcOAiPHChc28SZ U92wwEGAr4OmB7GhXAnBtrkTav1XnAaGyhLWlNZuVeXhjq/49ruabgW/gzUcGpfZawVm kRo9Ck90YF2T+ZGBtLNIjRNAP+GQTe/MiOlwzw5Dn5x4iCZZpnctzYAZsDJ4qENm+p+5 lhKg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:message-id:date:mime-version:user-agent :subject:content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=B4NLxiEMn45fm7ZP4Wwd+hPT7xASfT/B5aQNlTl+H7A=; b=DC9MNHdWhbRCUTwvpLw/EWaeys2iE/DO1fafFoc0KnIVyPWT5cNJNc+Jnso2z77BK1 Fn/OYevvPHeUvmNI7JXKmB3l0Ng3f7eopK6rGglk2U4oOZ8MLzDmX2lQQvjm/GrEckvw Ta13e9OgconyhOxfzYSRPq0mPmxmiMf5I5Zu1V8xpECQ5vEXvQ7th8dFdRKGbRojn/cu sCD8ba1jwszRmp5r735viuI0QXMwQ+69CUDDijlnU2YB2GcmvbRMYC/kv6TCqoCLK3JC PjDB0zfytW+wzj1CQ1IQfFBfTUxJx7wQEB6QteNnuT+oTQSR91kKe78FSlawgj+0/VGp 5QyA== X-Gm-Message-State: AOAM533Z/HhRAjDQhdJ7VQe08/JDeHHMIlV/nVkAuk/sTDqqpnOVTPZW 1mzHBCD6mM7Xq7mY0bBSgtw= X-Google-Smtp-Source: ABdhPJyfOJPcLez5/oODtByHWW20dnzZY19n9GVD3PszbXFfK9sYlpav3gVzNtkzqezlSG+tQd/TIw== X-Received: by 2002:a05:6402:50d0:b0:419:7df9:55c8 with SMTP id h16-20020a05640250d000b004197df955c8mr8245720edb.79.1650031354111; Fri, 15 Apr 2022 07:02:34 -0700 (PDT) Received: from ?IPV6:2001:b07:add:ec09:c399:bc87:7b6c:fb2a? ([2001:b07:add:ec09:c399:bc87:7b6c:fb2a]) by smtp.googlemail.com with ESMTPSA id dn7-20020a17090794c700b006e8b176143bsm1715171ejc.155.2022.04.15.07.02.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 Apr 2022 07:02:33 -0700 (PDT) Sender: Paolo Bonzini Message-ID: <42931581-24f3-d995-4971-5cdf3041d53f@redhat.com> Date: Fri, 15 Apr 2022 16:02:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [RFC PATCH v5 067/104] KVM: x86: Allow to update cached values in kvm_user_return_msrs w/o wrmsr Content-Language: en-US To: isaku.yamahata@intel.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: isaku.yamahata@gmail.com, Jim Mattson , erdemaktas@google.com, Connor Kuehl , Sean Christopherson References: <07b46b34aa86658fe8409926c3b8474dd6ff0d8c.1646422845.git.isaku.yamahata@intel.com> From: Paolo Bonzini In-Reply-To: <07b46b34aa86658fe8409926c3b8474dd6ff0d8c.1646422845.git.isaku.yamahata@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/4/22 20:49, isaku.yamahata@intel.com wrote: > From: Chao Gao > > Several MSRs are constant and only used in userspace(ring 3). But VMs may > have different values. KVM uses kvm_set_user_return_msr() to switch to > guest's values and leverages user return notifier to restore them when the > kernel is to return to userspace. To eliminate unnecessary wrmsr, KVM also > caches the value it wrote to an MSR last time. > > TDX module unconditionally resets some of these MSRs to architectural INIT > state on TD exit. It makes the cached values in kvm_user_return_msrs are > inconsistent with values in hardware. This inconsistency needs to be > fixed. Otherwise, it may mislead kvm_on_user_return() to skip restoring > some MSRs to the host's values. kvm_set_user_return_msr() can help correct > this case, but it is not optimal as it always does a wrmsr. So, introduce > a variation of kvm_set_user_return_msr() to update cached values and skip > that wrmsr. > > Signed-off-by: Chao Gao > Signed-off-by: Isaku Yamahata > --- > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/x86.c | 25 ++++++++++++++++++++----- > 2 files changed, 21 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 8406f8b5ab74..b6396d11139e 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1894,6 +1894,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, > int kvm_add_user_return_msr(u32 msr); > int kvm_find_user_return_msr(u32 msr); > int kvm_set_user_return_msr(unsigned index, u64 val, u64 mask); > +void kvm_user_return_update_cache(unsigned int index, u64 val); > > static inline bool kvm_is_supported_user_return_msr(u32 msr) > { > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 66400810d54f..45e8a02e99bf 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -427,6 +427,15 @@ static void kvm_user_return_msr_cpu_online(void) > } > } > > +static void kvm_user_return_register_notifier(struct kvm_user_return_msrs *msrs) > +{ > + if (!msrs->registered) { > + msrs->urn.on_user_return = kvm_on_user_return; > + user_return_notifier_register(&msrs->urn); > + msrs->registered = true; > + } > +} > + > int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask) > { > unsigned int cpu = smp_processor_id(); > @@ -441,15 +450,21 @@ int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask) > return 1; > > msrs->values[slot].curr = value; > - if (!msrs->registered) { > - msrs->urn.on_user_return = kvm_on_user_return; > - user_return_notifier_register(&msrs->urn); > - msrs->registered = true; > - } > + kvm_user_return_register_notifier(msrs); > return 0; > } > EXPORT_SYMBOL_GPL(kvm_set_user_return_msr); > > +/* Update the cache, "curr", and register the notifier */ > +void kvm_user_return_update_cache(unsigned int slot, u64 value) > +{ > + struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs); > + > + msrs->values[slot].curr = value; > + kvm_user_return_register_notifier(msrs); > +} > +EXPORT_SYMBOL_GPL(kvm_user_return_update_cache); > + > static void drop_user_return_notifiers(void) > { > unsigned int cpu = smp_processor_id(); Reviewed-by: Paolo Bonzini