From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 AF26C2264A7 for ; Fri, 27 Mar 2026 14:02:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774620156; cv=none; b=o9vhOc8zOK/egHjIKRfr4KbdNnDEbWjI0dlq2OZuUl/MYoVDcA5cNhIdKeB5+x0YCypx9b4tDIyTMmsLw4TdRC9xx4iM+d9UQWI2pzr6fWaP3OAWb/BtJAjEiW8inaJllzvCwAFO/O6AbaOdhA866lpRFI7D8VPPsdss0HzBCjE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774620156; c=relaxed/simple; bh=Qd4MhpMUzrMOwnMUgYIjNZ0YuQ9N3zBVyO7g4Wa1/uk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tuChsZyqD671Qjaq4agEy7xVaF000f9Xpqr7vd0KJjA9l8LtzzhGjcLMIzJy3VtXSg2zmn15NIAkRMwV9HDDUyFtJ4tAYS6QISUjdbjOy0GSkw/LdqAV9b2/MTcs9XFX2zGkl+Og9dCBrb66D3esy7nU72WI9XyBZDQiwBS3Gpk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dQQT60ak; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dQQT60ak" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9C62EC2BCB2; Fri, 27 Mar 2026 14:02:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774620156; bh=Qd4MhpMUzrMOwnMUgYIjNZ0YuQ9N3zBVyO7g4Wa1/uk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dQQT60akpNd7YdQt0HEhNFOyM9GUbsUQHE0EbA5Ze/rIbxuqieyu9W4aU0v+OJwO+ XdAoA9VHhpdl9bx4pq1ur8Ms80VSM4hEsTzdU/EMXjCJ1bkG6EjaApqJ6QwkxuMOzS U0+nM1cQAgLUiahVBZpIvdeAhg8Ctx9XIQxWDXgRNJonP3GfYFwI2/hIUzwU1xoUj0 xL2kYJijjPi5PFXXxyGLoVP3mw6Kuenfwkggb8YHwqvDq94LSIjzOphoPTEcfc0RlO trojG3ZvPOOzS8MAL0bhf17GTpIfD+fe/YUs3xWAbdu4dCvaFGdxsQ1xKYe2IEPzql KHZExorLYQTrg== From: Will Deacon To: kvmarm@lists.linux.dev Cc: linux-arm-kernel@lists.infradead.org, Will Deacon , Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Quentin Perret , Fuad Tabba , Vincent Donnefort , Mostafa Saleh , Alexandru Elisei Subject: [PATCH v4 32/38] KVM: arm64: Add some initial documentation for pKVM Date: Fri, 27 Mar 2026 14:00:31 +0000 Message-ID: <20260327140039.21228-33-will@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260327140039.21228-1-will@kernel.org> References: <20260327140039.21228-1-will@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add some initial documentation for pKVM to help people understand what is supported, the limitations of protected VMs when compared to non-protected VMs and also what is left to do. Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Tested-by: Mostafa Saleh Signed-off-by: Will Deacon --- .../admin-guide/kernel-parameters.txt | 4 +- Documentation/virt/kvm/arm/index.rst | 1 + Documentation/virt/kvm/arm/pkvm.rst | 106 ++++++++++++++++++ 3 files changed, 109 insertions(+), 2 deletions(-) create mode 100644 Documentation/virt/kvm/arm/pkvm.rst diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 03a550630644..44854a67bc63 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3247,8 +3247,8 @@ Kernel parameters for the host. To force nVHE on VHE hardware, add "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the command-line. - "nested" is experimental and should be used with - extreme caution. + "nested" and "protected" are experimental and should be + used with extreme caution. kvm-arm.vgic_v3_group0_trap= [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 diff --git a/Documentation/virt/kvm/arm/index.rst b/Documentation/virt/kvm/arm/index.rst index ec09881de4cf..0856b4942e05 100644 --- a/Documentation/virt/kvm/arm/index.rst +++ b/Documentation/virt/kvm/arm/index.rst @@ -10,6 +10,7 @@ ARM fw-pseudo-registers hyp-abi hypercalls + pkvm pvtime ptp_kvm vcpu-features diff --git a/Documentation/virt/kvm/arm/pkvm.rst b/Documentation/virt/kvm/arm/pkvm.rst new file mode 100644 index 000000000000..514992a79a83 --- /dev/null +++ b/Documentation/virt/kvm/arm/pkvm.rst @@ -0,0 +1,106 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +Protected KVM (pKVM) +==================== + +**NOTE**: pKVM is currently an experimental, development feature and +subject to breaking changes as new isolation features are implemented. +Please reach out to the developers at kvmarm@lists.linux.dev if you have +any questions. + +Overview +======== + +Booting a host kernel with '``kvm-arm.mode=protected``' enables +"Protected KVM" (pKVM). During boot, pKVM installs a stage-2 identity +map page-table for the host and uses it to isolate the hypervisor +running at EL2 from the rest of the host running at EL1/0. + +pKVM permits creation of protected virtual machines (pVMs) by passing +the ``KVM_VM_TYPE_ARM_PROTECTED`` machine type identifier to the +``KVM_CREATE_VM`` ioctl(). The hypervisor isolates pVMs from the host by +unmapping pages from the stage-2 identity map as they are accessed by a +pVM. Hypercalls are provided for a pVM to share specific regions of its +IPA space back with the host, allowing for communication with the VMM. +A Linux guest must be configured with ``CONFIG_ARM_PKVM_GUEST=y`` in +order to issue these hypercalls. + +See hypercalls.rst for more details. + +Isolation mechanisms +==================== + +pKVM relies on a number of mechanisms to isolate PVMs from the host: + +CPU memory isolation +-------------------- + +Status: Isolation of anonymous memory and metadata pages. + +Metadata pages (e.g. page-table pages and '``struct kvm_vcpu``' pages) +are donated from the host to the hypervisor during pVM creation and +are consequently unmapped from the stage-2 identity map until the pVM is +destroyed. + +Similarly to regular KVM, pages are lazily mapped into the guest in +response to stage-2 page faults handled by the host. However, when +running a pVM, these pages are first pinned and then unmapped from the +stage-2 identity map as part of the donation procedure. This gives rise +to some user-visible differences when compared to non-protected VMs, +largely due to the lack of MMU notifiers: + +* Memslots cannot be moved or deleted once the pVM has started running. +* Read-only memslots and dirty logging are not supported. +* With the exception of swap, file-backed pages cannot be mapped into a + pVM. +* Donated pages are accounted against ``RLIMIT_MLOCK`` and so the VMM + must have a sufficient resource limit or be granted ``CAP_IPC_LOCK``. + The lack of a runtime reclaim mechanism means that memory locked for + a pVM will remain locked until the pVM is destroyed. +* Changes to the VMM address space (e.g. a ``MAP_FIXED`` mmap() over a + mapping associated with a memslot) are not reflected in the guest and + may lead to loss of coherency. +* Accessing pVM memory that has not been shared back will result in the + delivery of a SIGSEGV. +* If a system call accesses pVM memory that has not been shared back + then it will either return ``-EFAULT`` or forcefully reclaim the + memory pages. Reclaimed memory is zeroed by the hypervisor and a + subsequent attempt to access it in the pVM will return ``-EFAULT`` + from the ``VCPU_RUN`` ioctl(). + +CPU state isolation +------------------- + +Status: **Unimplemented.** + +DMA isolation using an IOMMU +---------------------------- + +Status: **Unimplemented.** + +Proxying of Trustzone services +------------------------------ + +Status: FF-A and PSCI calls from the host are proxied by the pKVM +hypervisor. + +The FF-A proxy ensures that the host cannot share pVM or hypervisor +memory with Trustzone as part of a "confused deputy" attack. + +The PSCI proxy ensures that CPUs always have the stage-2 identity map +installed when they are executing in the host. + +Protected VM firmware (pvmfw) +----------------------------- + +Status: **Unimplemented.** + +Resources +========= + +Quentin Perret's KVM Forum 2022 talk entitled "Protected KVM on arm64: A +technical deep dive" remains a good resource for learning more about +pKVM, despite some of the details having changed in the meantime: + +https://www.youtube.com/watch?v=9npebeVFbFw -- 2.53.0.1018.g2bb0e51243-goog