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Fri, 13 Nov 2026 09:12:59 -0800 (PST) Received: from jp-linux.Home ([2001:8a0:f59c:a900:b5a2:ed52:66a7:3ac7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-49c69406640sm6001643f8f.12.2026.11.13.09.12.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Nov 2026 09:12:58 -0800 (PST) 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 v6 0/3] virt: bao: add Bao hypervisor IPC and I/O dispatcher drivers Date: Fri, 13 Nov 2026 17:12:52 +0000 Message-ID: X-Mailer: git-send-email 2.53.0 X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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 channels are declared on the kernel command line. - 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 v5 ---------------- All findings of the Sashiko review of v5 are addressed. They are all in the I/O dispatcher; patches 1 and 3 are unchanged. - A device model is torn down in order: dispatching stops first, every I/O client is stopped before any is destroyed (the ioeventfds are released only once their thread is gone), then the queued, in-flight and still pending requests are completed. The dispatcher is no longer paused and resumed per client, which re-queued dispatch work during teardown and issued hypercalls when BAO_IOCTL_CREATE_DM failed. - IO_CLIENT_ATTACH publishes a request only once it has been copied to userspace, so a concurrent IO_REQUEST_COMPLETE cannot complete it twice. - ioeventfds follow KVM: two of them conflict when a write could match both, whatever eventfd they use; a request matches only the exact length; reads, and writes that no ioeventfd matches, are handed to the VMM instead of being answered or dropped by the kernel. - Matching a request against an I/O range rejects zero or oversized access widths and wrap-around. - An irqfd consumes the eventfd counter when signaled, and deassigning an unknown irqfd fails with -ENOENT. - The I/O dispatcher is 64-bit only: the Remote I/O fields did not fit the RV32 hypercall registers. Also, requests already pending when a device model is created (a frontend that started first, a VMM that restarted) are picked up at creation instead of waiting for a notification that does not come again. Changes since v4 ---------------- - BAO_IOCTL_CREATE_DM requires CAP_SYS_RAWIO, is refused under lockdown and claims a non-RAM region with request_mem_region(), mirroring /dev/mem. The notification line is checked against the interrupt controller and requested exclusively, and its mapping is never disposed, since it may be shared with whoever owns the line. - Requests that cannot be delivered are completed instead of stranded. The requests handed to the VMM are tracked: a completion only provides the value, and a VMM that exits leaves nothing behind. - ioeventfds and irqfds are bounded per device model, and a device model id is bound to one file descriptor at a time. - RISC-V: the hypercall status is the SBI value (a1), and both drivers depend on RISCV_SBI. - mmap goes through .mmap_prepare and only allows shared mappings; .compat_ioctl is set; the IPC driver never unwinds a registered device; bao_ipcshmem.channels= is documented in kernel-parameters.txt; rebased on v7.4-rc1. Changes since v3 ---------------- - No device tree (Krzysztof Kozlowski): the IPC channels are declared on the kernel command line and, following drivers/virt/acrn, the VMM creates each device model through /dev/bao (BAO_IOCTL_CREATE_DM), which returns a per-device-model file descriptor. - No architecture code (Will Deacon): the hypercalls use arm_smccc_hvc()/arm_smccc_1_2_hvc() and sbi_ecall() from a driver-private header. - The "consolidate the IPC hypercall ID" patch is folded in (Andrew Jones), and the ioctl type is 0xA7. Testing ------- Built on v7.4-rc1 with GCC 15 (W=1) for arm64, arm and riscv (RV64 and RV32), at every commit, and with clang 21 (W=1) 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 guest and a FreeRTOS guest, and the I/O dispatcher with a Linux backend serving console, network and block device models to a FreeRTOS guest and to Linux guests, including killing and restarting the VMMs, plus a userspace test of the /dev/bao error paths (privilege, region and line checks, duplicate ids, limits, completions, ioeventfd and irqfd rules) run next to the live VMMs. 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 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. - The notification line is a line of the interrupt controller the device tree's root node points at through interrupt-parent; a guest whose root node has none cannot use the I/O dispatcher yet. v5: https://lore.kernel.org/all/cover.1794038390.git.jpeixoto@osyx.tech/ v4: https://lore.kernel.org/all/cover.1790357735.git.jpeixoto@osyx.tech/ 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 .../admin-guide/kernel-parameters.txt | 15 + .../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 | 210 ++++++++ drivers/virt/bao/io-dispatcher/Kconfig | 20 + drivers/virt/bao/io-dispatcher/Makefile | 4 + drivers/virt/bao/io-dispatcher/bao_drv.h | 421 ++++++++++++++++ drivers/virt/bao/io-dispatcher/dm.c | 460 +++++++++++++++++ drivers/virt/bao/io-dispatcher/driver.c | 71 +++ drivers/virt/bao/io-dispatcher/intc.c | 186 +++++++ drivers/virt/bao/io-dispatcher/io_client.c | 475 ++++++++++++++++++ .../virt/bao/io-dispatcher/io_dispatcher.c | 184 +++++++ drivers/virt/bao/io-dispatcher/ioeventfd.c | 359 +++++++++++++ drivers/virt/bao/io-dispatcher/irqfd.c | 330 ++++++++++++ drivers/virt/bao/ipcshmem/Kconfig | 16 + drivers/virt/bao/ipcshmem/Makefile | 3 + drivers/virt/bao/ipcshmem/ipcshmem.c | 421 ++++++++++++++++ include/uapi/linux/bao.h | 126 +++++ 22 files changed, 3323 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: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4 -- 2.53.0