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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5AB70C433F5 for ; Tue, 5 Oct 2021 08:48:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3988A6137C for ; Tue, 5 Oct 2021 08:48:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232511AbhJEIt4 (ORCPT ); Tue, 5 Oct 2021 04:49:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:54136 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230526AbhJEItz (ORCPT ); Tue, 5 Oct 2021 04:49:55 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 91C806120F; Tue, 5 Oct 2021 08:48:05 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mXg7H-00EpOY-I9; Tue, 05 Oct 2021 09:48:03 +0100 Date: Tue, 05 Oct 2021 09:48:03 +0100 Message-ID: <87sfxfrh6k.wl-maz@kernel.org> From: Marc Zyngier To: Fuad Tabba Cc: kvmarm@lists.cs.columbia.edu, will@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, mark.rutland@arm.com, christoffer.dall@arm.com, pbonzini@redhat.com, drjones@redhat.com, oupton@google.com, qperret@google.com, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel-team@android.com Subject: Re: [PATCH v6 12/12] KVM: arm64: Handle protected guests at 32 bits In-Reply-To: <20210922124704.600087-13-tabba@google.com> References: <20210922124704.600087-1-tabba@google.com> <20210922124704.600087-13-tabba@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: tabba@google.com, kvmarm@lists.cs.columbia.edu, will@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, mark.rutland@arm.com, christoffer.dall@arm.com, pbonzini@redhat.com, drjones@redhat.com, oupton@google.com, qperret@google.com, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, 22 Sep 2021 13:47:04 +0100, Fuad Tabba wrote: > > Protected KVM does not support protected AArch32 guests. However, > it is possible for the guest to force run AArch32, potentially > causing problems. Add an extra check so that if the hypervisor > catches the guest doing that, it can prevent the guest from > running again by resetting vcpu->arch.target and returning > ARM_EXCEPTION_IL. > > If this were to happen, The VMM can try and fix it by re- > initializing the vcpu with KVM_ARM_VCPU_INIT, however, this is > likely not possible for protected VMs. > > Adapted from commit 22f553842b14 ("KVM: arm64: Handle Asymmetric > AArch32 systems") > > Signed-off-by: Fuad Tabba > --- > arch/arm64/kvm/hyp/nvhe/switch.c | 40 ++++++++++++++++++++++++++++++++ > 1 file changed, 40 insertions(+) > > diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c > index 2bf5952f651b..d66226e49013 100644 > --- a/arch/arm64/kvm/hyp/nvhe/switch.c > +++ b/arch/arm64/kvm/hyp/nvhe/switch.c > @@ -235,6 +235,43 @@ static const exit_handler_fn *kvm_get_exit_handler_array(struct kvm *kvm) > return hyp_exit_handlers; > } > > +/* > + * Some guests (e.g., protected VMs) might not be allowed to run in AArch32. > + * The ARMv8 architecture does not give the hypervisor a mechanism to prevent a > + * guest from dropping to AArch32 EL0 if implemented by the CPU. If the > + * hypervisor spots a guest in such a state ensure it is handled, and don't > + * trust the host to spot or fix it. The check below is based on the one in > + * kvm_arch_vcpu_ioctl_run(). > + * > + * Returns false if the guest ran in AArch32 when it shouldn't have, and > + * thus should exit to the host, or true if a the guest run loop can continue. > + */ > +static bool handle_aarch32_guest(struct kvm_vcpu *vcpu, u64 *exit_code) > +{ > + struct kvm *kvm = (struct kvm *) kern_hyp_va(vcpu->kvm); There is no need for an extra cast. kern_hyp_va() already provides a cast to the type of the parameter. > + bool is_aarch32_allowed = > + FIELD_GET(ARM64_FEATURE_MASK(ID_AA64PFR0_EL0), > + get_pvm_id_aa64pfr0(vcpu)) >= > + ID_AA64PFR0_ELx_32BIT_64BIT; > + > + > + if (kvm_vm_is_protected(kvm) && > + vcpu_mode_is_32bit(vcpu) && > + !is_aarch32_allowed) { Do we really need to go through this is_aarch32_allowed check? Protected VMs don't have AArch32, and we don't have the infrastructure to handle 32bit at all. For non-protected VMs, we already have what we need at EL1. So the extra check only adds complexity. > + /* > + * As we have caught the guest red-handed, decide that it isn't > + * fit for purpose anymore by making the vcpu invalid. The VMM > + * can try and fix it by re-initializing the vcpu with > + * KVM_ARM_VCPU_INIT, however, this is likely not possible for > + * protected VMs. > + */ > + vcpu->arch.target = -1; > + *exit_code = ARM_EXCEPTION_IL; > + return false; > + } > + > + return true; > +} > + > /* Switch to the guest for legacy non-VHE systems */ > int __kvm_vcpu_run(struct kvm_vcpu *vcpu) > { > @@ -297,6 +334,9 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu) > /* Jump in the fire! */ > exit_code = __guest_enter(vcpu); > > + if (unlikely(!handle_aarch32_guest(vcpu, &exit_code))) > + break; > + > /* And we're baaack! */ > } while (fixup_guest_exit(vcpu, &exit_code)); > Thanks, M. -- Without deviation from the norm, progress is not possible.