From patchwork Fri Jul 26 18:51:44 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Bonzini X-Patchwork-Id: 13743049 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7B0763032A for ; Fri, 26 Jul 2024 18:52:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722019927; cv=none; b=dbGNO2VLXt7Jwe5gTUKDzYN6MS8bQqneR+qsdevyMuW8lF2iMcdwL/hWsE5WGFbK1StHK1+B3Drj83CRdnRRnHESBrKwGWX//tdwotceSGHxarUSdHYvK9+8kq72CCjBmspTb9Ekt61nZOvDhuF9sI3DhfsDQNaaLnIvPzc3/Mo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722019927; c=relaxed/simple; bh=O26rJ7Gcfv4ARMLR28jWxqFOljVbUnxyI2aeb/KHyHI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=O/8FG7PqYXv8ZBlcOMJPMNotJFlB0/n6/Of4IZ/vatZn0Dtc6VewwbSf/0ogrHBrxsnLK/4KQKTDRCIDdpD8lLKqlQ3UmYRgTJu15qszulbMXL1R095QIA2lrBI8SAL2I7aM3G7ofc51+WKhfLTVXpxPgtRAggs9A1YBVBTAbjw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ItBUkJfa; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ItBUkJfa" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722019924; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Nzd3Ramz8UsVExhcniTAeg+8/OlVGantjS5vCPA9244=; b=ItBUkJfah1i9WtgxHQ5z2U6QIgEqaJWi7DIfYtUz6uX7iaNdBTGYnawHefIVPV0rX/q86T YeNZJDsQ66BZQrcIntplYeksHqkI2o7+G0/43/dVfomRRrYEyHZFsO0J6sNWC0EhMzOsSA +d3YCyrJTxBmI09octibXscEjFUQBpQ= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-12-8IdCqyXBOUWxMALqfQablw-1; Fri, 26 Jul 2024 14:52:00 -0400 X-MC-Unique: 8IdCqyXBOUWxMALqfQablw-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AFFD419560AD; Fri, 26 Jul 2024 18:51:59 +0000 (UTC) Received: from virtlab1023.lab.eng.rdu2.redhat.com (virtlab1023.lab.eng.rdu2.redhat.com [10.8.1.187]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 0048E3000194; Fri, 26 Jul 2024 18:51:58 +0000 (UTC) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: seanjc@google.com, michael.roth@amd.com Subject: [PATCH v2 01/14] KVM: x86: disallow pre-fault for SNP VMs before initialization Date: Fri, 26 Jul 2024 14:51:44 -0400 Message-ID: <20240726185157.72821-2-pbonzini@redhat.com> In-Reply-To: <20240726185157.72821-1-pbonzini@redhat.com> References: <20240726185157.72821-1-pbonzini@redhat.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 KVM_PRE_FAULT_MEMORY for an SNP guest can race with sev_gmem_post_populate() in bad ways. The following sequence for instance can potentially trigger an RMP fault: thread A, sev_gmem_post_populate: called thread B, sev_gmem_prepare: places below 'pfn' in a private state in RMP thread A, sev_gmem_post_populate: *vaddr = kmap_local_pfn(pfn + i); thread A, sev_gmem_post_populate: copy_from_user(vaddr, src + i * PAGE_SIZE, PAGE_SIZE); RMP #PF Fix this by only allowing KVM_PRE_FAULT_MEMORY to run after a guest's initial private memory contents have been finalized via KVM_SEV_SNP_LAUNCH_FINISH. Beyond fixing this issue, it just sort of makes sense to enforce this, since the KVM_PRE_FAULT_MEMORY documentation states: "KVM maps memory as if the vCPU generated a stage-2 read page fault" which sort of implies we should be acting on the same guest state that a vCPU would see post-launch after the initial guest memory is all set up. Co-developed-by: Michael Roth Signed-off-by: Michael Roth Signed-off-by: Paolo Bonzini --- Documentation/virt/kvm/api.rst | 6 ++++++ arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/mmu/mmu.c | 3 +++ arch/x86/kvm/svm/sev.c | 8 ++++++++ arch/x86/kvm/svm/svm.c | 1 + arch/x86/kvm/x86.c | 3 +++ 6 files changed, 22 insertions(+) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index ec1cd8aa1d56..7b512286f8d2 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6402,6 +6402,12 @@ for the current vCPU state. KVM maps memory as if the vCPU generated a stage-2 read page fault, e.g. faults in memory as needed, but doesn't break CoW. However, KVM does not mark any newly created stage-2 PTE as Accessed. +In the case of confidential VM types where there is an initial set up of +private guest memory before the guest is 'finalized'/measured, this ioctl +should only be issued after completing all the necessary setup to put the +guest into a 'finalized' state so that the above semantics can be reliably +ensured. + In some cases, multiple vCPUs might share the page tables. In this case, the ioctl can be called in parallel. diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 950a03e0181e..94e7b5a4fafe 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1305,6 +1305,7 @@ struct kvm_arch { u8 vm_type; bool has_private_mem; bool has_protected_state; + bool pre_fault_allowed; struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES]; struct list_head active_mmu_pages; struct list_head zapped_obsolete_pages; diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 901be9e420a4..26ef5b6ac3c1 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4743,6 +4743,9 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, u64 end; int r; + if (!vcpu->kvm->arch.pre_fault_allowed) + return -EOPNOTSUPP; + /* * reload is efficient when called repeatedly, so we can do it on * every iteration. diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index a16c873b3232..6589091e8ce0 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2549,6 +2549,14 @@ static int snp_launch_finish(struct kvm *kvm, struct kvm_sev_cmd *argp) data->gctx_paddr = __psp_pa(sev->snp_context); ret = sev_issue_cmd(kvm, SEV_CMD_SNP_LAUNCH_FINISH, data, &argp->error); + /* + * Now that there will be no more SNP_LAUNCH_UPDATE ioctls, private pages + * can be given to the guest simply by marking the RMP entry as private. + * This can happen on first access and also with KVM_PRE_FAULT_MEMORY. + */ + if (!ret) + kvm->arch.pre_fault_allowed = true; + kfree(id_auth); e_free_id_block: diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index c115d26844f7..d6f252555ab3 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -4949,6 +4949,7 @@ static int svm_vm_init(struct kvm *kvm) to_kvm_sev_info(kvm)->need_init = true; kvm->arch.has_private_mem = (type == KVM_X86_SNP_VM); + kvm->arch.pre_fault_allowed = !kvm->arch.has_private_mem; } if (!pause_filter_count || !pause_filter_thresh) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index af6c8cf6a37a..52778689cef4 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12646,6 +12646,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) kvm->arch.vm_type = type; kvm->arch.has_private_mem = (type == KVM_X86_SW_PROTECTED_VM); + /* Decided by the vendor code for other VM types. */ + kvm->arch.pre_fault_allowed = + type == KVM_X86_DEFAULT_VM || type == KVM_X86_SW_PROTECTED_VM; ret = kvm_page_track_init(kvm); if (ret)