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[34.82.80.254]) by smtp.gmail.com with ESMTPSA id b10-20020a170902650a00b0015e8d4eb269sm2289156plk.179.2022.05.13.15.53.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 May 2022 15:53:09 -0700 (PDT) Date: Fri, 13 May 2022 22:53:05 +0000 From: David Matlack To: Lai Jiangshan Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Lai Jiangshan , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" Subject: Re: [PATCH V2 1/7] KVM: X86/MMU: Add using_special_root_page() Message-ID: References: <20220503150735.32723-1-jiangshanlai@gmail.com> <20220503150735.32723-2-jiangshanlai@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220503150735.32723-2-jiangshanlai@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 03, 2022 at 11:07:29PM +0800, Lai Jiangshan wrote: > From: Lai Jiangshan > > In some case, special roots are used in mmu. It is often using > to_shadow_page(mmu->root.hpa) to check if special roots are used. > > Add using_special_root_page() to directly check if special roots are > used or needed to be used even mmu->root.hpa is not set. > > Prepare for making to_shadow_page(mmu->root.hpa) return non-NULL via > using special shadow pages. > > Signed-off-by: Lai Jiangshan > --- > arch/x86/kvm/mmu/mmu.c | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 909372762363..7f20796af351 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -1711,6 +1711,14 @@ static void drop_parent_pte(struct kvm_mmu_page *sp, > mmu_spte_clear_no_track(parent_pte); > } > > +static bool using_special_root_page(struct kvm_mmu *mmu) Could you enumerate all the scenarios that use special roots and which roots are the special ones? I think that would help a lot with reviewing this series and would be useful to encode in a comment, probably above this function here, for future readers. Also the term "special" is really vague. Maybe once you enumerate all the scenarios a common theme will arise and we can pick a better name, unless you have any ideas off the top of your head. > +{ > + if (mmu->root_role.direct) > + return mmu->root_role.level == PT32E_ROOT_LEVEL; > + else > + return 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; > @@ -4241,10 +4249,10 @@ 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. Special roots can not be put into > + * mmu->prev_roots[]. > */ > - if (VALID_PAGE(mmu->root.hpa) && !to_shadow_page(mmu->root.hpa)) > + if (VALID_PAGE(mmu->root.hpa) && using_special_root_page(mmu)) > kvm_mmu_free_roots(kvm, mmu, KVM_MMU_ROOT_CURRENT); > > if (VALID_PAGE(mmu->root.hpa)) > -- > 2.19.1.6.gb485710b >