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 E913735E555 for ; Mon, 19 Jan 2026 12:48:28 +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=1768826909; cv=none; b=Ca09V027Ja/HZrhiJhPWZ83UWfq0j5Qeij+RurwCi6+yXX5UJ+p490i/HHDX/DlvUbV1m0wJaIo85/DFYeqf1wvEhGIhPSJlKEwa+JeJ5a82tHh2BF1iRX6z6cowaD3GPzR4l2WAFpb8ce7OvDYwNBdgUMOP4dTtXL3X2+E5Ols= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768826909; c=relaxed/simple; bh=F9yw5vRr7Fmcg+1tg9VmxWqRbBfYixh3CsApvUh2BIs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jy0hLZbeCtCxnLjWHXL3k89AdX3N0cPr+sGG/Bro8FLBpRRPRuDXaHsiS8kBnAfFh6Mg7r8hPHgNnbdYcNtKoPBJ5siGN1YMeCOfguDx8ZxpOc9CqlaNjr5Vk3QcKDhPpHIcBpHW770b6a8JBsO0Fjp0iqQoP7fNN2VW+YQMRpM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UXA90RTD; 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="UXA90RTD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 15651C116C6; Mon, 19 Jan 2026 12:48:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768826908; bh=F9yw5vRr7Fmcg+1tg9VmxWqRbBfYixh3CsApvUh2BIs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UXA90RTDMNLVJrsedO8ygJPuHGg8ZjN/kwtU8uir4Zcb1go23ofg62GuMlxVvO1pm xdwSI/krLHt1V14B2QhWT7MZIGt0kzrbsbnG6g6rTbJqITd503IZAWEqw4EGTDapaM JOQrgvnyIzVJM7L+TtLmhKchmizRPW1iB7NIy6YaflHVYTz4s8GE2B+16BGBdneRzD I62LLf/b0dpru9gu3wnLDCHb1degq3oR3VKW3zyV7al8nRI8OKLkWHDbgXIPAWKzRE gqjiAcbIvC3CxSB+x2s7/GeRJH4xXNmguUADwlyTasPzPPFIj1s2Bh/of4lxPqVPBo DFqC/kcMzmjOg== 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 Subject: [PATCH v2 31/35] KVM: arm64: Add some initial documentation for pKVM Date: Mon, 19 Jan 2026 12:46:24 +0000 Message-ID: <20260119124629.2563-32-will@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260119124629.2563-1-will@kernel.org> References: <20260119124629.2563-1-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. Signed-off-by: Will Deacon --- .../admin-guide/kernel-parameters.txt | 4 +- Documentation/virt/kvm/arm/index.rst | 1 + Documentation/virt/kvm/arm/pkvm.rst | 103 ++++++++++++++++++ 3 files changed, 106 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 a8d0afde7f85..9939dc5654d2 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3141,8 +3141,8 @@ 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..8258c93bed6e --- /dev/null +++ b/Documentation/virt/kvm/arm/pkvm.rst @@ -0,0 +1,103 @@ +.. 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. + +If ``CONFIG_PROTECTED_VM_UAPI=y``, 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. 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 -- 2.52.0.457.g6b5491de43-goog