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[34.34.145.44]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432bd5ff0b2sm5090628f8f.42.2026.01.06.07.59.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Jan 2026 07:59:40 -0800 (PST) Date: Tue, 6 Jan 2026 15:59:37 +0000 From: Vincent Donnefort To: Will Deacon Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Quentin Perret , Fuad Tabba , Mostafa Saleh Subject: Re: [PATCH 27/30] KVM: arm64: Add some initial documentation for pKVM Message-ID: References: <20260105154939.11041-1-will@kernel.org> <20260105154939.11041-28-will@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260105154939.11041-28-will@kernel.org> On Mon, Jan 05, 2026 at 03:49:35PM +0000, Will Deacon wrote: > 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 | 101 ++++++++++++++++++ > 3 files changed, 104 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..1882bde8cc0b > --- /dev/null > +++ b/Documentation/virt/kvm/arm/pkvm.rst > @@ -0,0 +1,101 @@ > +.. 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``. Perhaps worth to add that there's no runtime reclaim either so the accounting will only grow until the VM 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 > -- > 2.52.0.351.gbe84eed79e-goog >