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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1C6E5C433EF for ; Fri, 4 Feb 2022 15:40:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1359778AbiBDPkK (ORCPT ); Fri, 4 Feb 2022 10:40:10 -0500 Received: from foss.arm.com ([217.140.110.172]:52386 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1359680AbiBDPkJ (ORCPT ); Fri, 4 Feb 2022 10:40:09 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 207641396; Fri, 4 Feb 2022 07:40:09 -0800 (PST) Received: from monolith.localdoman (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E2DA13F774; Fri, 4 Feb 2022 07:40:05 -0800 (PST) Date: Fri, 4 Feb 2022 15:40:15 +0000 From: Alexandru Elisei To: Marc Zyngier Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Andre Przywara , Christoffer Dall , Jintack Lim , Haibo Xu , Ganapatrao Kulkarni , Chase Conklin , "Russell King (Oracle)" , James Morse , Suzuki K Poulose , karl.heubaum@oracle.com, mihai.carabas@oracle.com, miguel.luis@oracle.com, kernel-team@android.com Subject: Re: [PATCH v6 22/64] KVM: arm64: nv: Respect virtual HCR_EL2.TWX setting Message-ID: References: <20220128121912.509006-1-maz@kernel.org> <20220128121912.509006-23-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220128121912.509006-23-maz@kernel.org> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi Marc, On Fri, Jan 28, 2022 at 12:18:30PM +0000, Marc Zyngier wrote: > From: Jintack Lim > > Forward exceptions due to WFI or WFE instructions to the virtual EL2 if > they are not coming from the virtual EL2 and virtual HCR_EL2.TWX is set. > > Signed-off-by: Jintack Lim > Signed-off-by: Marc Zyngier > --- > arch/arm64/include/asm/kvm_nested.h | 2 ++ > arch/arm64/kvm/Makefile | 2 +- > arch/arm64/kvm/handle_exit.c | 11 ++++++++++- > arch/arm64/kvm/nested.c | 28 ++++++++++++++++++++++++++++ > 4 files changed, 41 insertions(+), 2 deletions(-) > create mode 100644 arch/arm64/kvm/nested.c > > diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h > index 5a85be6d8eb3..79d382fa02ea 100644 > --- a/arch/arm64/include/asm/kvm_nested.h > +++ b/arch/arm64/include/asm/kvm_nested.h > @@ -65,4 +65,6 @@ static inline u64 translate_cnthctl_el2_to_cntkctl_el1(u64 cnthctl) > (cnthctl & (CNTHCTL_EVNTI | CNTHCTL_EVNTDIR | CNTHCTL_EVNTEN))); > } > > +int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe); > + > #endif /* __ARM64_KVM_NESTED_H */ > diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile > index b67c4ebd72b1..dbaf42ff65f1 100644 > --- a/arch/arm64/kvm/Makefile > +++ b/arch/arm64/kvm/Makefile > @@ -14,7 +14,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \ > inject_fault.o va_layout.o handle_exit.o \ > guest.o debug.o reset.o sys_regs.o \ > vgic-sys-reg-v3.o fpsimd.o pmu.o pkvm.o \ > - arch_timer.o trng.o emulate-nested.o \ > + arch_timer.o trng.o emulate-nested.o nested.o \ > vgic/vgic.o vgic/vgic-init.o \ > vgic/vgic-irqfd.o vgic/vgic-v2.o \ > vgic/vgic-v3.o vgic/vgic-v4.o \ > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > index 0cedef6e0d80..a1b1bbf3d598 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -119,7 +119,16 @@ static int handle_no_fpsimd(struct kvm_vcpu *vcpu) > */ > static int kvm_handle_wfx(struct kvm_vcpu *vcpu) > { > - if (kvm_vcpu_get_esr(vcpu) & ESR_ELx_WFx_ISS_WFE) { > + bool is_wfe = !!(kvm_vcpu_get_esr(vcpu) & ESR_ELx_WFx_ISS_WFE); > + > + if (vcpu_has_nv(vcpu)) { > + int ret = handle_wfx_nested(vcpu, is_wfe); > + > + if (ret != -EINVAL) > + return ret; I find this rather clunky. The common pattern is that a function returns early when it encounters an error, but here this pattern is reversed: -EINVAL means that handle_wfx_nested() failed in handling the WFx, so proceed as usual; conversly, anything but -EINVAL means handle_wfx_nested() was successful in handling WFx, so exit early from kvm_handle_wfx(). That would be ok by itself, but if we dig deeper, handle_wfx_nested() ends up calling kvm_inject_nested(), where -EINVAL is actually an error code. Granted, that should never happen, because kvm_handle_wfx() first checks vcpu_has_nv(), but still feels like something that could be improved. Maybe changing handle_wfx_nested() like this would be better: --- a/arch/arm64/kvm/nested.c +++ b/arch/arm64/kvm/nested.c @@ -14,15 +14,18 @@ * the virtual HCR_EL2.TWX is set. Otherwise, let the host hypervisor * handle this. */ -int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe) +bool handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe, int *error) { u64 hcr_el2 = __vcpu_sys_reg(vcpu, HCR_EL2); + *error = 0; if (vcpu_is_el2(vcpu)) - return -EINVAL; + return false; - if ((is_wfe && (hcr_el2 & HCR_TWE)) || (!is_wfe && (hcr_el2 & HCR_TWI))) - return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu)); + if ((is_wfe && (hcr_el2 & HCR_TWE)) || (!is_wfe && (hcr_el2 & HCR_TWI))) { + *error = kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu)); + return true; + } - return -EINVAL; + return false; } Now the return value means one thing only (did handle_wfx_nested() handle the trap?) and we still capture the error code. Or perhaps folding handle_wfx_nested() into kvm_handle_wfx() would be preferable. What do you think? Thanks, Alex > + } > + > + if (is_wfe) { > trace_kvm_wfx_arm64(*vcpu_pc(vcpu), true); > vcpu->stat.wfe_exit_stat++; > kvm_vcpu_on_spin(vcpu, vcpu_mode_priv(vcpu)); > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c > new file mode 100644 > index 000000000000..5e1104f8e765 > --- /dev/null > +++ b/arch/arm64/kvm/nested.c > @@ -0,0 +1,28 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Copyright (C) 2017 - Columbia University and Linaro Ltd. > + * Author: Jintack Lim > + */ > + > +#include > +#include > + > +#include > + > +/* > + * Inject wfx to the virtual EL2 if this is not from the virtual EL2 and > + * the virtual HCR_EL2.TWX is set. Otherwise, let the host hypervisor > + * handle this. > + */ > +int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe) > +{ > + u64 hcr_el2 = __vcpu_sys_reg(vcpu, HCR_EL2); > + > + if (vcpu_is_el2(vcpu)) > + return -EINVAL; > + > + if ((is_wfe && (hcr_el2 & HCR_TWE)) || (!is_wfe && (hcr_el2 & HCR_TWI))) > + return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu)); > + > + return -EINVAL; > +} > -- > 2.30.2 >