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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 75BC0C79FB6 for ; Wed, 9 Sep 2026 11:52:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=fw55BCT+Axacwui+FpoaafStt22fYXHK/NEwxTxZQBQ=; b=YOIFk30qRLpy4OAeEEsQDPOiLL 85hLYhC1Lqm8ITxGJkFX+2C9dKdMwQPcjb31Un9MMHaGK8Yv7kRn91+mKacdHjlDmzuaKxWIspy2d KEAT8dP1nJL3WJMPFYFlA4uQKtnrwF6US7SOs51NUZQJa0YOzvIAduEi0fz4l/95C6GcRYSGppxwL TgbNGajzuTsa+35up5BW5Mj8SPO5odi+xjICcjhNm6d0fnlm+KMsKRbHPKbVxFdQa9+HgBseqPdLe mSC4icCKDL9gsVCqBBeIO4eXPwLEtFleK79f4M3RRaQquzpTehlTbXxLZRbu80oXFBGSCSijkZUwG 9DbFU5Tg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x4Gqc-0000000Bd0n-2WfI; Wed, 09 Sep 2026 11:52:14 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x4GqZ-0000000Bd0S-1Vs1 for linux-arm-kernel@lists.infradead.org; Wed, 09 Sep 2026 11:52:12 +0000 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 43E221477; Wed, 9 Sep 2026 04:52:04 -0700 (PDT) Received: from [10.2.197.99] (ewhatever.cambridge.arm.com [10.2.197.99]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D1C1B3F528; Wed, 9 Sep 2026 04:52:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1788954727; bh=2vyi1ZM3AtA2rx0F5ICpxmrqDzaZPmSJCKlrDhxuxaI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=LMahlmWr+Jeo63JcaLXAkkURJxGLjmJfNWrb8zwoRFFLoK/h5UsOWMaBdZU0SO25i vpPIG/pGA4VOt4wjXeY1ZDuVeyB5w2+UPEOCPZU5uxNym4pNc8LwxX6LY5R1i/6rwx i7iT7eFwrbeBj8Ohl7pAWkvgLDWOJAY9P/HsUp/o= Message-ID: <6152fc41-65f0-460f-90b4-1454c11bcba6@arm.com> Date: Wed, 9 Sep 2026 12:52:03 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v17 10/20] KVM: arm64: coco: Disable Steal time accounting for coco guests To: Fuad Tabba Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, maz@kernel.org, will@kernel.org, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, steven.price@arm.com, aneesh.kumar@kernel.org, oupton@kernel.org, gshan@redhat.com, joey.gouly@arm.com, yuzenghui@huawei.com, linux-coco@lists.linux.dev, gankulkarni@os.amperecomputing.com, sdonthineni@nvidia.com, alpergun@google.com, fj0570is@fujitsu.com, WeiLin.Chang@arm.com, lpieralisi@kernel.org, enju.kohei@fujitsu.com References: <20260908162223.1683432-1-suzuki.poulose@arm.com> <20260908162223.1683432-11-suzuki.poulose@arm.com> Content-Language: en-US From: Suzuki K Poulose In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260909_045211_524846_D99CECC1 X-CRM114-Status: GOOD ( 20.22 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 09/09/2026 12:45, Fuad Tabba wrote: > Hi Suzuki, > > On Tue, 8 Sept 2026 at 17:23, Suzuki K Poulose wrote: >> >> PVTIME support is advertised by KVM_CAP_STEAL_TIME, which doesn't take into >> account the kvm instance. Even with that, a VMM could skip the CAP check and >> proceed to configure the PVTIME as we don't do further check on the DEVICE_CTRL. >> Tighten this up by passing the KVM instance around wherever possible and >> catch things early >> >> Signed-off-by: Suzuki K Poulose > > ... > >> -bool kvm_arm_pvtime_supported(void) >> +bool kvm_arm_pvtime_supported(struct kvm *kvm) >> { >> - return !!sched_info_on(); >> + return !!sched_info_on() && (!kvm || !kvm_vm_is_confidential(kvm)); >> } > > I think it would be better to leave KVM_CAP_STEAL_TIME reported and > instead reject the configuration for these VMs, returning -EPERM from > the KVM_ARM_VCPU_PVTIME_CTRL attr. A capability query should report > what the kernel supports, not whether a given VM may use it; gating it > per-VM here is also inconsistent, since the !kvm clause leaves the > system-fd cap at 1 while the VM-fd cap reads 0. And -EPERM says that But isn't that we want from a VMM perspective ? i.e., enable PVTIME if it is supported for the given VM (type). Rather than PVTIME is supported by the KVM, so I can go enable it by default. But, we endup getting a failure while we enable it. I encountered this with kvmtool, where CAP_STEAL_TIME is reported true and even the HAS_DEVICE_ATTR goes through fine, but SET_DEVICE_ATTR seemed to fail. Isn't it better to allow the VM to decide if the capability is supported for the given VM type, like we are doing for other capabilities ? > steal-time exists but isn't permitted for a confidential VM, whereas > -ENXIO reads as "no such feature". Cheers Suzuki > > Cheers, > /fuad > >> >> int kvm_arm_pvtime_set_attr(struct kvm_vcpu *vcpu, >> @@ -81,7 +81,7 @@ int kvm_arm_pvtime_set_attr(struct kvm_vcpu *vcpu, >> int ret = 0; >> int idx; >> >> - if (!kvm_arm_pvtime_supported() || >> + if (!kvm_arm_pvtime_supported(kvm) || >> attr->attr != KVM_ARM_VCPU_PVTIME_IPA) >> return -ENXIO; >> >> @@ -110,7 +110,7 @@ int kvm_arm_pvtime_get_attr(struct kvm_vcpu *vcpu, >> u64 __user *user = (u64 __user *)attr->addr; >> u64 ipa; >> >> - if (!kvm_arm_pvtime_supported() || >> + if (!kvm_arm_pvtime_supported(vcpu->kvm) || >> attr->attr != KVM_ARM_VCPU_PVTIME_IPA) >> return -ENXIO; >> >> @@ -126,7 +126,7 @@ int kvm_arm_pvtime_has_attr(struct kvm_vcpu *vcpu, >> { >> switch (attr->attr) { >> case KVM_ARM_VCPU_PVTIME_IPA: >> - if (kvm_arm_pvtime_supported()) >> + if (kvm_arm_pvtime_supported(vcpu->kvm)) >> return 0; >> } >> return -ENXIO; >> -- >> 2.43.0 >>