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 BB420C433EF for ; Thu, 26 May 2022 21:29:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239372AbiEZV3A (ORCPT ); Thu, 26 May 2022 17:29:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49112 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229485AbiEZV25 (ORCPT ); Thu, 26 May 2022 17:28:57 -0400 Received: from mail-pg1-x536.google.com (mail-pg1-x536.google.com [IPv6:2607:f8b0:4864:20::536]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4875DA88A5 for ; Thu, 26 May 2022 14:28:56 -0700 (PDT) Received: by mail-pg1-x536.google.com with SMTP id v15so2311482pgk.11 for ; Thu, 26 May 2022 14:28:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=n/dQumpwP7TjnB5SFXHOsq0ojlkNiebJVgxbXnsVWEw=; b=UORJmqEl1ZcTStO8P44GY6cM5VBCI4XXU11RYFlagzJPjwgLYfR9fWKFey4MYWSAtR v6ZMhIP8kBUlqH+CMgZgxU5WofSdJGzn19kuixH59EZk9g2tEAr7gbO8gPRgedJPOzMA mPef4VS8XoKCVT/bJiD31KTs7du7pbYzTMDguk0MpNBwU9sfSBZr54e/ZpZaCcLHI/Rc tzWGa3K74/Y+4F5nT3uc0RoUahIwXQMYu2QsQVtvXeOZEHl64ToezAaklWdfbsGv2fJT nD6b3CuKWQnXjRwEDb878ABVSl5/lYkaTSRriEltMT5Pnw0eiJT1doQ4WE5HWlR72QnD 9fIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=n/dQumpwP7TjnB5SFXHOsq0ojlkNiebJVgxbXnsVWEw=; b=W7RLjPi1MU32MaAhZ2wIGiak7zzsV+90YMJOCJ6Y+W25HdEE8yJzyBVPPqom2v4yh2 IrKSYA4HVkJHe1ZZ55RsKdHz6zL89vI8cSpE04sbdmOBnjgDtQfTRNM8wsoWtuIu59vV YKGGPl8mQNcBppZNK1F0f6M/lp9R+EWwZyFRpBHsYnxGalq6r8Lj32PT8QHifNfsE6iD fIytpV+AO7on2fByclVj5w3SI+ULc02EZ6jApv3iEiZFKKL4CTukn4PtZ2yReIQvAHBw auCRolhD3zdF9dPpdpxAL6kEB4gmFJPYvZsWHrOS9htLKINI92H/XtKDTiJe0JmtAvGv YpBA== X-Gm-Message-State: AOAM530ugw9IXhSr8NnLSQx3UZhcL+mzK91HqKkQ6Tdt5cvpW60nc7cR PzYDAGJsAA/80cQT6orW/UvphA== X-Google-Smtp-Source: ABdhPJzlDei3c5LPTtjJF4767PxFoKhAc+XnedidW9jrARRoSw5p5T61izwk+1esqhopcAZjZotTBw== X-Received: by 2002:a63:7d3:0:b0:3f6:885:cd22 with SMTP id 202-20020a6307d3000000b003f60885cd22mr35097498pgh.143.1653600535500; Thu, 26 May 2022 14:28:55 -0700 (PDT) Received: from google.com (254.80.82.34.bc.googleusercontent.com. [34.82.80.254]) by smtp.gmail.com with ESMTPSA id n24-20020a17090ac69800b001e26c391d28sm83742pjt.54.2022.05.26.14.28.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 May 2022 14:28:54 -0700 (PDT) Date: Thu, 26 May 2022 21:28:50 +0000 From: David Matlack To: Lai Jiangshan Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Maxim Levitsky , Lai Jiangshan Subject: Re: [PATCH V3 02/12] KVM: X86/MMU: Add using_local_root_page() Message-ID: References: <20220521131700.3661-1-jiangshanlai@gmail.com> <20220521131700.3661-3-jiangshanlai@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220521131700.3661-3-jiangshanlai@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 21, 2022 at 09:16:50PM +0800, Lai Jiangshan wrote: > From: Lai Jiangshan > > In some cases, local root pages are used for MMU. It is often using > to_shadow_page(mmu->root.hpa) to check if local root pages are used. > > Add using_local_root_page() to directly check if local root pages are > used or needed to be used even mmu->root.hpa is not set. > > Prepare for making to_shadow_page(mmu->root.hpa) returns non-NULL via > using local shadow [root] pages. > > Signed-off-by: Lai Jiangshan > --- > arch/x86/kvm/mmu/mmu.c | 40 +++++++++++++++++++++++++++++++++++++--- > 1 file changed, 37 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index efe5a3dca1e0..624b6d2473f7 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -1690,6 +1690,39 @@ static void drop_parent_pte(struct kvm_mmu_page *sp, > mmu_spte_clear_no_track(parent_pte); > } > > +/* > + * KVM uses the VCPU's local root page (vcpu->mmu->pae_root) when either the > + * shadow pagetable is using PAE paging or the host is shadowing nested NPT for > + * 32bit L1 hypervisor. How about using the terms "private" and "shared" instead of "local" and "non-local"? I think that more accurately conveys what is special about these pages: they are private to the vCPU using them. And then "shared" is more intuitive to understand than "non-local" (which is used elsewhere in this series). > + * > + * It includes cases: > + * nonpaging when !tdp_enabled (direct paging) > + * shadow paging for 32 bit guest when !tdp_enabled (shadow paging) > + * NPT in 32bit host (not shadowing nested NPT) (direct paging) > + * shadow nested NPT for 32bit L1 hypervisor in 32bit host (shadow paging) > + * shadow nested NPT for 32bit L1 hypervisor in 64bit host (shadow paging) > + * > + * For the first four cases, mmu->root_role.level is PT32E_ROOT_LEVEL and the > + * shadow pagetable is using PAE paging. > + * > + * For the last case, it is > + * mmu->root_role.level > PT32E_ROOT_LEVEL && > + * !mmu->root_role.direct && mmu->cpu_role.base.level <= PT32E_ROOT_LEVEL > + * And if this condition is true, it must be the last case. > + * > + * With the two conditions combined, the checking condition is: > + * mmu->root_role.level == PT32E_ROOT_LEVEL || > + * (!mmu->root_role.direct && mmu->cpu_role.base.level <= PT32E_ROOT_LEVEL) > + * > + * (There is no "mmu->root_role.level > PT32E_ROOT_LEVEL" here, because it is > + * already ensured that mmu->root_role.level >= PT32E_ROOT_LEVEL) > + */ > +static bool using_local_root_page(struct kvm_mmu *mmu) > +{ > + return mmu->root_role.level == PT32E_ROOT_LEVEL || > + (!mmu->root_role.direct && mmu->cpu_role.base.level <= PT32E_ROOT_LEVEL); > +} > + > static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu, int direct) > { > struct kvm_mmu_page *sp; > @@ -4252,10 +4285,11 @@ static bool fast_pgd_switch(struct kvm *kvm, struct kvm_mmu *mmu, > { > /* > * For now, limit the caching to 64-bit hosts+VMs in order to avoid > - * having to deal with PDPTEs. We may add support for 32-bit hosts/VMs > - * later if necessary. > + * having to deal with PDPTEs. Local roots can not be put into > + * mmu->prev_roots[] because mmu->pae_root can not be shared for > + * different roots at the same time. This comment ends up being a little confusing by the end of this series because using_local_root_page() does not necessarily imply pae_root is in use. i.e. case 5 (shadow nested NPT for 32bit L1 hypervisor in 64bit host) does not use pae_root. How about rewording this commit to say something like: If the vCPU is using a private root, it might be using pae_root, which cannot be shared for different roots at the same time. > */ > - if (VALID_PAGE(mmu->root.hpa) && !to_shadow_page(mmu->root.hpa)) > + if (unlikely(using_local_root_page(mmu))) > kvm_mmu_free_roots(kvm, mmu, KVM_MMU_ROOT_CURRENT); > > if (VALID_PAGE(mmu->root.hpa)) > -- > 2.19.1.6.gb485710b >