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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id i4sm25236470wrm.32.2020.03.23.09.57.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2020 09:57:17 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson Cc: Paolo Bonzini , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon , Junaid Shahid , Liran Alon , Boris Ostrovsky , John Haxby , Miaohe Lin , Tom Lendacky Subject: Re: [PATCH v3 04/37] KVM: nVMX: Invalidate all roots when emulating INVVPID without EPT In-Reply-To: <20200323165001.GR28711@linux.intel.com> References: <20200320212833.3507-1-sean.j.christopherson@intel.com> <20200320212833.3507-5-sean.j.christopherson@intel.com> <87v9mv84qu.fsf@vitty.brq.redhat.com> <20200323160432.GJ28711@linux.intel.com> <87lfnr820r.fsf@vitty.brq.redhat.com> <20200323165001.GR28711@linux.intel.com> Date: Mon, 23 Mar 2020 17:57:16 +0100 Message-ID: <87imiv80wj.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sean Christopherson writes: > On Mon, Mar 23, 2020 at 05:33:08PM +0100, Vitaly Kuznetsov wrote: >> Sean Christopherson writes: >> >> > On Mon, Mar 23, 2020 at 04:34:17PM +0100, Vitaly Kuznetsov wrote: >> >> Sean Christopherson writes: >> >> >> >> > From: Junaid Shahid >> >> > >> >> > Free all roots when emulating INVVPID for L1 and EPT is disabled, as >> >> > outstanding changes to the page tables managed by L1 need to be >> >> > recognized. Because L1 and L2 share an MMU when EPT is disabled, and >> >> > because VPID is not tracked by the MMU role, all roots in the current >> >> > MMU (root_mmu) need to be freed, otherwise a future nested VM-Enter or >> >> > VM-Exit could do a fast CR3 switch (without a flush/sync) and consume >> >> > stale SPTEs. >> >> > >> >> > Fixes: 5c614b3583e7b ("KVM: nVMX: nested VPID emulation") >> >> > Signed-off-by: Junaid Shahid >> >> > [sean: ported to upstream KVM, reworded the comment and changelog] >> >> > Signed-off-by: Sean Christopherson >> >> > --- >> >> > arch/x86/kvm/vmx/nested.c | 14 ++++++++++++++ >> >> > 1 file changed, 14 insertions(+) >> >> > >> >> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c >> >> > index 9624cea4ed9f..bc74fbbf33c6 100644 >> >> > --- a/arch/x86/kvm/vmx/nested.c >> >> > +++ b/arch/x86/kvm/vmx/nested.c >> >> > @@ -5250,6 +5250,20 @@ static int handle_invvpid(struct kvm_vcpu *vcpu) >> >> > return kvm_skip_emulated_instruction(vcpu); >> >> > } >> >> > >> >> > + /* >> >> > + * Sync the shadow page tables if EPT is disabled, L1 is invalidating >> >> > + * linear mappings for L2 (tagged with L2's VPID). Free all roots as >> >> > + * VPIDs are not tracked in the MMU role. >> >> > + * >> >> > + * Note, this operates on root_mmu, not guest_mmu, as L1 and L2 share >> >> > + * an MMU when EPT is disabled. >> >> > + * >> >> > + * TODO: sync only the affected SPTEs for INVDIVIDUAL_ADDR. >> >> > + */ >> >> > + if (!enable_ept) >> >> > + kvm_mmu_free_roots(vcpu, &vcpu->arch.root_mmu, >> >> > + KVM_MMU_ROOTS_ALL); >> >> > + >> >> >> >> This is related to my remark on the previous patch; the comment above >> >> makes me think I'm missing something obvious, enlighten me please) >> >> >> >> My understanding is that L1 and L2 will share arch.root_mmu not only >> >> when EPT is globally disabled, we seem to switch between >> >> root_mmu/guest_mmu only when nested_cpu_has_ept(vmcs12) but different L2 >> >> guests may be different on this. Do we need to handle this somehow? >> > >> > guest_mmu is used iff nested EPT is enabled, which requires enable_ept=1. >> > enable_ept is global and cannot be changed without reloading kvm_intel. >> > >> > This most definitely over-invalidates, e.g. it blasts away L1's page >> > tables. But, fixing that requires tracking VPID in mmu_role and/or adding >> > support for using guest_mmu when L1 isn't using TDP, i.e. nested EPT is >> > disabled. Assuming the vast majority of nested deployments enable EPT in >> > L0, the cost of both options likely outweighs the benefits. >> > >> >> Yes but my question rather was: what if global 'enable_ept' is true but >> nested EPT is not being used by L1, don't we still need to do >> kvm_mmu_free_roots(&vcpu->arch.root_mmu) here? > > No, because L0 isn't shadowing the L1->L2 page tables, i.e. there can't be > unsync'd SPTEs for L2. The vpid_sync_*() above flushes the TLB for L2's > effective VPID, which is all that's required. Ah, stupid me, it's actually EPT and not nested EPT which we care about here. Thank you for the clarification! Reviewed-by: Vitaly Kuznetsov -- Vitaly