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Sun, 27 Sep 2026 04:49:47 -0700 (PDT) From: =?UTF-8?q?Jo=C3=A3o=20Peixoto?= To: gregkh@linuxfoundation.org, will@kernel.org Cc: catalin.marinas@arm.com, andrew.jones@oss.qualcomm.com, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, krzk+dt@kernel.org, robh@kernel.org, conor+dt@kernel.org, corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, jose@osyx.tech, davidmcerdeira@osyx.tech, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, linux-doc@vger.kernel.org, devicetree@vger.kernel.org Subject: [PATCH v4 0/3] virt: bao: add Bao hypervisor IPC and I/O dispatcher drivers Date: Sun, 27 Sep 2026 12:49:21 +0100 Message-ID: X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This series adds guest-side drivers for the Bao static-partitioning hypervisor: an IPC shared-memory driver, an I/O dispatcher that lets a backend guest service VirtIO I/O for frontend guests, their UAPI and a MAINTAINERS entry. Bao is a lightweight static-partitioning hypervisor for embedded and safety-critical systems (https://github.com/bao-project). - The IPC shared-memory driver lets Bao guests exchange data through a shared-memory region split into a read and a write channel, exposed as a misc character device (read(), write(), mmap()). - The I/O dispatcher bridges Bao's Remote I/O mechanism to a userspace VMM: the VMM creates each device model from /dev/bao, receives the frontend's MMIO accesses and completes them, with ioeventfd/irqfd support for the fast paths. Changes since v3 ---------------- The two design comments on v3 changed the shape of the series, which went from six patches to three. - No device tree (Krzysztof Kozlowski): both bindings and the "bao" vendor prefix are dropped. The IPC channels are a software contract between the hypervisor and the guest and are now declared on the kernel command line (bao_ipcshmem.channels=...). The set of device models a backend serves is a contract between the hypervisor and the VMM, so, following drivers/virt/acrn, the I/O dispatcher exposes a single /dev/bao control device and the VMM creates each device model with BAO_IOCTL_CREATE_DM (shared-memory region + notification line), which returns a per-DM file descriptor; the DM lives as long as the descriptor. The notification line is resolved against the device tree's root interrupt parent, like any device's interrupt. - No architecture code (Will Deacon): the hypercall helpers moved to drivers/virt/bao/bao_hypercall.h and use arm_smccc_hvc() for the IPC hypercall and, because the Remote I/O hypercall returns the request in x1-x6, the SMCCC v1.2 arm_smccc_1_2_hvc(). RISC-V uses sbi_ecall() for IPC and a local ecall for Remote I/O (see open items). 32-bit Arm has no SMCCC v1.2 helper, so the I/O dispatcher is limited to arm64 and RISC-V for now; the IPC driver still supports 32-bit Arm through SMCCC v1.1 (HAVE_ARM_SMCCC). - The standalone "consolidate the IPC hypercall ID" patch is folded into the driver patches (Andrew Jones). - All findings of the Sashiko review of v3 are addressed, among them: the DM id is taken from the file descriptor instead of userspace; the irqfd/ioeventfd teardown races and the ioeventfd deassign fall-through are fixed; the interrupt handler is per DM and the request_irq() name is persistent; queued requests are capped and requests that cannot be delivered are completed back to the hypervisor; the UAPI structures have no implicit padding; signals return -ERESTARTSYS; the IPC driver orders the shared-memory writes before the notify hypercall, refuses writable mappings of the read region, validates page-aligned regions and has an llseek. Details are in the per-patch changelogs. - The ioctl type is now 0xA7: 7.3-rc1 registered 0xA6 for memory allocation profiling. - Found while testing: the two modules were both named bao.ko (now bao_ipcshmem and bao_io_dispatcher), the ioeventfd kernel thread could exit before kthread_stop(), per-DM dispatcher state was kept in static arrays, a list walk used the wrong structure type, the UAPI header did not include linux/ioctl.h, and the dispatcher workqueue now passes WQ_PERCPU as required since 7.x. Testing ------- Built on v7.3-rc1 with GCC (W=1, sparse) for arm64, arm and riscv, as modules and built-in, and with clang for arm64 and riscv. Run-time tested under Bao v2.0.0 on QEMU aarch64 virt and QEMU riscv64 virt with the bao-demos demos: the IPC driver exchanging messages in both directions between a Linux 7.3-rc1 guest and a FreeRTOS guest (linux+freertos demo), and the I/O dispatcher with a Linux backend serving console, network and block device models to a FreeRTOS guest and two Linux guests (virtio demo). 32-bit Arm is compile-tested only. Open items ---------- - RISC-V: the Bao SBI extension still uses the experimental extension space (0x08000ba0), and the Remote I/O hypercall returns the request in a2-a7, which does not follow the SBI calling convention (Andrew Jones, v2). Changing that means a hypervisor ABI change (status in a0/a1, request through shared memory); the RISC-V support is marked experimental until then, or it can be split out of this series if preferred. - Bao does not implement the SMCCC vendor-hypervisor UID call, so the drivers cannot detect the hypervisor yet; adding it is planned on the hypervisor side. v3: https://lore.kernel.org/all/cover.1786010512.git.jpeixoto@osyx.tech/ João Peixoto (3): virt: bao: add IPC shared-memory driver virt: bao: add I/O dispatcher driver MAINTAINERS: add Bao hypervisor entry .../userspace-api/ioctl/ioctl-number.rst | 2 + MAINTAINERS | 8 + drivers/virt/Kconfig | 2 + drivers/virt/Makefile | 1 + drivers/virt/bao/Kconfig | 5 + drivers/virt/bao/Makefile | 4 + drivers/virt/bao/bao_hypercall.h | 190 ++++++++ drivers/virt/bao/io-dispatcher/Kconfig | 20 + drivers/virt/bao/io-dispatcher/Makefile | 4 + drivers/virt/bao/io-dispatcher/bao_drv.h | 389 ++++++++++++++++ drivers/virt/bao/io-dispatcher/dm.c | 334 ++++++++++++++ drivers/virt/bao/io-dispatcher/driver.c | 70 +++ drivers/virt/bao/io-dispatcher/intc.c | 150 +++++++ drivers/virt/bao/io-dispatcher/io_client.c | 423 ++++++++++++++++++ .../virt/bao/io-dispatcher/io_dispatcher.c | 159 +++++++ drivers/virt/bao/io-dispatcher/ioeventfd.c | 326 ++++++++++++++ drivers/virt/bao/io-dispatcher/irqfd.c | 315 +++++++++++++ drivers/virt/bao/ipcshmem/Kconfig | 16 + drivers/virt/bao/ipcshmem/Makefile | 3 + drivers/virt/bao/ipcshmem/ipcshmem.c | 358 +++++++++++++++ include/uapi/linux/bao.h | 116 +++++ 21 files changed, 2895 insertions(+) create mode 100644 drivers/virt/bao/Kconfig create mode 100644 drivers/virt/bao/Makefile create mode 100644 drivers/virt/bao/bao_hypercall.h create mode 100644 drivers/virt/bao/io-dispatcher/Kconfig create mode 100644 drivers/virt/bao/io-dispatcher/Makefile create mode 100644 drivers/virt/bao/io-dispatcher/bao_drv.h create mode 100644 drivers/virt/bao/io-dispatcher/dm.c create mode 100644 drivers/virt/bao/io-dispatcher/driver.c create mode 100644 drivers/virt/bao/io-dispatcher/intc.c create mode 100644 drivers/virt/bao/io-dispatcher/io_client.c create mode 100644 drivers/virt/bao/io-dispatcher/io_dispatcher.c create mode 100644 drivers/virt/bao/io-dispatcher/ioeventfd.c create mode 100644 drivers/virt/bao/io-dispatcher/irqfd.c create mode 100644 drivers/virt/bao/ipcshmem/Kconfig create mode 100644 drivers/virt/bao/ipcshmem/Makefile create mode 100644 drivers/virt/bao/ipcshmem/ipcshmem.c create mode 100644 include/uapi/linux/bao.h base-commit: cee9395acd8043be0644b25c34bfa86623f2b935 -- 2.43.0