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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id eo22sm14566576ejc.0.2021.04.08.08.57.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Apr 2021 08:57:55 -0700 (PDT) Subject: Re: [PATCH v2 07/17] KVM: x86/mmu: Check PDPTRs before allocating PAE roots To: Sean Christopherson Cc: Wanpeng Li , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm , LKML , Ben Gardon , Brijesh Singh , Tom Lendacky References: <20210305011101.3597423-1-seanjc@google.com> <20210305011101.3597423-8-seanjc@google.com> From: Paolo Bonzini Message-ID: <8b7129ed-0377-7b91-c741-44ac2202081a@redhat.com> Date: Thu, 8 Apr 2021 17:57:54 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/04/21 17:48, Sean Christopherson wrote: > Freaking PDPTRs. I was really hoping we could keep the lock and pages_available() > logic outside of the helpers. What if kvm_mmu_load() reads the PDPTRs and > passes them into mmu_alloc_shadow_roots()? Or is that too ugly? The patch I have posted (though untested) tries to do that in a slightly less ugly way by pushing make_mmu_pages_available down to mmu_alloc_*_roots. Paolo > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index efb41f31e80a..e3c4938cd665 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3275,11 +3275,11 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu) > return 0; > } > > -static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) > +static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu, u64 pdptrs[4]) > { > struct kvm_mmu *mmu = vcpu->arch.mmu; > - u64 pdptrs[4], pm_mask; > gfn_t root_gfn, root_pgd; > + u64 pm_mask; > hpa_t root; > int i; > > @@ -3291,11 +3291,8 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) > > if (mmu->root_level == PT32E_ROOT_LEVEL) { > for (i = 0; i < 4; ++i) { > - pdptrs[i] = mmu->get_pdptr(vcpu, i); > - if (!(pdptrs[i] & PT_PRESENT_MASK)) > - continue; > - > - if (mmu_check_root(vcpu, pdptrs[i] >> PAGE_SHIFT)) > + if ((pdptrs[i] & PT_PRESENT_MASK) && > + mmu_check_root(vcpu, pdptrs[i] >> PAGE_SHIFT)) > return 1; > } > } > @@ -4844,21 +4841,33 @@ EXPORT_SYMBOL_GPL(kvm_mmu_reset_context); > > int kvm_mmu_load(struct kvm_vcpu *vcpu) > { > - int r; > + struct kvm_mmu *mmu = vcpu->arch.mmu; > + u64 pdptrs[4]; > + int r, i; > > - r = mmu_topup_memory_caches(vcpu, !vcpu->arch.mmu->direct_map); > + r = mmu_topup_memory_caches(vcpu, !mmu->direct_map); > if (r) > goto out; > r = mmu_alloc_special_roots(vcpu); > if (r) > goto out; > + > + /* > + * On SVM, reading PDPTRs might access guest memory, which might fault > + * and thus might sleep. Grab the PDPTRs before acquiring mmu_lock. > + */ > + if (!mmu->direct_map && mmu->root_level == PT32E_ROOT_LEVEL) { > + for (i = 0; i < 4; ++i) > + pdptrs[i] = mmu->get_pdptr(vcpu, i); > + } > + > write_lock(&vcpu->kvm->mmu_lock); > if (make_mmu_pages_available(vcpu)) > r = -ENOSPC; > else if (vcpu->arch.mmu->direct_map) > r = mmu_alloc_direct_roots(vcpu); > else > - r = mmu_alloc_shadow_roots(vcpu); > + r = mmu_alloc_shadow_roots(vcpu, pdptrs); > write_unlock(&vcpu->kvm->mmu_lock); > if (r) > goto out; >