From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH] KVM: s390: force bp isolation for VSIE Date: Wed, 14 Feb 2018 11:06:57 +0100 Message-ID: <16458103-a499-ce6d-4160-682cd9e8f926@redhat.com> References: <20180214083422.44175-1-borntraeger@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20180214083422.44175-1-borntraeger@de.ibm.com> Content-Language: en-US Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: Christian Borntraeger , Janosch Frank Cc: KVM , Cornelia Huck , linux-s390 List-ID: On 14.02.2018 09:34, Christian Borntraeger wrote: > If the guest runs with bp isolation when doing a SIE instruction, > we must also run the nested guest with bp isolation when emulating > that SIE instruction. > > Signed-off-by: Christian Borntraeger > --- > arch/s390/kvm/vsie.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c > index ec772700ff96..b8e7660d7207 100644 > --- a/arch/s390/kvm/vsie.c > +++ b/arch/s390/kvm/vsie.c > @@ -821,6 +821,7 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) > { > struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s; > struct kvm_s390_sie_block *scb_o = vsie_page->scb_o; > + int guest_bp_isolation; > int rc; > > handle_last_fault(vcpu, vsie_page); > @@ -831,6 +832,15 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) > s390_handle_mcck(); > > srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx); > + > + /* save current guest state of bp isolation override */ > + guest_bp_isolation = test_thread_flag(TIF_ISOLATE_BP_GUEST); If I am not wrong, this is not "guest state". The guest state is vcpu->arch.sie_block->fpf . This is host state of a thread. > + > + /* if guest runs with bp isolation force it on nested guest */ > + if (test_kvm_facility(vcpu->kvm, 82) && > + vcpu->arch.sie_block->fpf & FPF_BPBC) > + set_thread_flag(TIF_ISOLATE_BP_GUEST); > + > local_irq_disable(); > guest_enter_irqoff(); > local_irq_enable(); > @@ -840,6 +850,11 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) > local_irq_disable(); > guest_exit_irqoff(); > local_irq_enable(); > + > + /* restore guest state for bp isolation override */ > + if (!guest_bp_isolation) > + clear_thread_flag(TIF_ISOLATE_BP_GUEST); > + > vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu); > > if (rc == -EINTR) { > You are trying to optimize the following case here: 1. TIF_ISOLATE_BP_GUEST is not set 2. The guest has facility 82 and enabled FPF_BPBC As the vSIE guest can change its FPF_BPBC, there is basically no guarantee to that. So, when entering/leaving the nested guest, you act like the hardware would be doing FPF_BPBC - as it could be disabled for the nested guest / the nested guest can change the state itself. However I wonder what the semantics of FPF_BPBC should be. Shouldn't it be the case that if the guest has enabled FPF_BPBC, that it is forced on for the nested guest? (HW is missing a control to force it on). Unfortunately, I don't have access to documentation, can you clarify? -- Thanks, David / dhildenb