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[209.51.188.17]) by mx.google.com with ESMTPS id x77si22573138ybe.284.2021.03.09.13.36.30 for (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Tue, 09 Mar 2021 13:36:30 -0800 (PST) Received-SPF: pass (google.com: domain of qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; Authentication-Results: mx.google.com; spf=pass (google.com: domain of qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom="qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org"; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from localhost ([::1]:32970 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lJk1m-0004XH-2p for alex.bennee@linaro.org; Tue, 09 Mar 2021 16:36:30 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:35256) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lJk0v-0004VD-G0; Tue, 09 Mar 2021 16:35:37 -0500 Received: from mail.kernel.org ([198.145.29.99]:45012) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lJk0h-0005cm-C7; Tue, 09 Mar 2021 16:35:34 -0500 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 915AC64F78; Tue, 9 Mar 2021 21:35:17 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1lJk0Z-000dZe-IM; Tue, 09 Mar 2021 21:35:15 +0000 Date: Tue, 09 Mar 2021 21:35:14 +0000 Message-ID: <87y2ewqact.wl-maz@kernel.org> From: Marc Zyngier To: Andrew Jones Subject: Re: [PATCH] hw/arm/virt: KVM: The IPA lower bound is 32 In-Reply-To: <20210309200606.kjjbxyyzijv2qsd4@kamzik.brq.redhat.com> References: <20210309185939.188431-1-drjones@redhat.com> <87eegoxhd5.wl-maz@kernel.org> <20210309200606.kjjbxyyzijv2qsd4@kamzik.brq.redhat.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: 62.31.163.78 X-SA-Exim-Rcpt-To: drjones@redhat.com, qemu-devel@nongnu.org, qemu-arm@nongnu.org, peter.maydell@linaro.org, eric.auger@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Received-SPF: pass client-ip=198.145.29.99; envelope-from=maz@kernel.org; helo=mail.kernel.org X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org, qemu-arm@nongnu.org, qemu-devel@nongnu.org, eric.auger@redhat.com Errors-To: qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org Sender: "Qemu-devel" X-TUID: TyvpA8rOz4Mz On Tue, 09 Mar 2021 20:06:06 +0000, Andrew Jones wrote: > > On Tue, Mar 09, 2021 at 07:21:58PM +0000, Marc Zyngier wrote: > > Hi Andrew, > > > > On Tue, 09 Mar 2021 18:59:39 +0000, > > Andrew Jones wrote: > > > > > > The virt machine already checks KVM_CAP_ARM_VM_IPA_SIZE to get the > > > upper bound of the IPA size. If that bound is lower than the highest > > > possible GPA for the machine, then QEMU will error out. However, the > > > IPA is set to 40 when the highest GPA is less than or equal to 40, > > > even when KVM may only support an IPA limit as low as 32. This means > > > KVM may fail the VM creation unnecessarily. Additionally, 40 is > > > selected with the value 0, which means use the default, and that gets > > > around a check in some versions of KVM, causing a difficult to debug > > > fail. Always use the IPA size that corresponds to the highest possible > > > GPA, unless it's lower than 32, in which case use 32. > > > > > > Signed-off-by: Andrew Jones > > > --- > > > hw/arm/virt.c | 9 ++++----- > > > 1 file changed, 4 insertions(+), 5 deletions(-) > > > > > > diff --git a/hw/arm/virt.c b/hw/arm/virt.c > > > index 371147f3ae9c..7bf563715b4e 100644 > > > --- a/hw/arm/virt.c > > > +++ b/hw/arm/virt.c > > > @@ -2547,14 +2547,13 @@ static int virt_kvm_type(MachineState *ms, const char *type_str) > > > "require an IPA range (%d bits) larger than " > > > "the one supported by the host (%d bits)", > > > requested_pa_size, max_vm_pa_size); > > > - exit(1); > > > + exit(1); > > > } > > > + > > > /* > > > - * By default we return 0 which corresponds to an implicit legacy > > > - * 40b IPA setting. Otherwise we return the actual requested PA > > > - * logsize > > > + * KVM requires the IPA size to be at least 32 bits. > > > */ > > > - return requested_pa_size > 40 ? requested_pa_size : 0; > > > + return requested_pa_size < 32 ? 32 : requested_pa_size; > > > > Doesn't this break on older kernels (pre 233a7cb23531, which is > > anything up 4.19), where the 'type' parameter passed at VM creation > > time was expected to be 0 and nothing else? > > Doh, of course! > > > > > I had a quick go at qemu a couple of weeks back and came up with the > > following hack, but never actually tested it (there is no way qemu can > > fit in the initramfs I am feeding to this damn machine...). > > > > Thanks, > > > > M. > > > > diff --git a/hw/arm/virt.c b/hw/arm/virt.c > > index 371147f3ae..3301bb8dba 100644 > > --- a/hw/arm/virt.c > > +++ b/hw/arm/virt.c > > @@ -2534,8 +2534,11 @@ static HotplugHandler *virt_machine_get_hotplug_handler(MachineState *machine, > > static int virt_kvm_type(MachineState *ms, const char *type_str) > > { > > VirtMachineState *vms = VIRT_MACHINE(ms); > > - int max_vm_pa_size = kvm_arm_get_max_vm_ipa_size(ms); > > + int max_vm_pa_size; > > int requested_pa_size; > > + bool fixed_ipa; > > + > > + max_vm_pa_size = kvm_arm_get_max_vm_ipa_size(ms, &fixed_ipa); > > > > /* we freeze the memory map to compute the highest gpa */ > > virt_set_memmap(vms); > > @@ -2550,11 +2553,12 @@ static int virt_kvm_type(MachineState *ms, const char *type_str) > > exit(1); > > } > > /* > > - * By default we return 0 which corresponds to an implicit legacy > > - * 40b IPA setting. Otherwise we return the actual requested PA > > - * logsize > > + * We return the requested PA log size, unless KVM only supports > > + * the implicit legacy 40b IPA setting, in which case we return 0. > > */ > > - return requested_pa_size > 40 ? requested_pa_size : 0; > > + if (fixed_ipa) > > + return 0; > > + return requested_pa_size; > > Looks good to me. I think we should still ensure requested_pa_size is at > least 32 though. Yes, absolutely. > I can add that and test this tomorrow. Should I post it with your > authorship? No, please keep it with yours (add a Suggested-by: tag if you really want to). If you can give it a good shake, that'd be great. I'll try and repost the kernel fixes tomorrow. Thanks, M. -- Without deviation from the norm, progress is not possible.