[RFC PATCH v3 2/6] virt: bao: add IPC shared-memory driver
João Peixoto
jpeixoto at osyx.tech
Fri Aug 7 00:39:29 PDT 2026
Add a driver that lets guests running on the Bao static-partitioning
hypervisor communicate through shared memory. Each guest is assigned a
read and a write region within a shared-memory area described in the
device tree.
Userspace accesses the regions through a misc character device using
read(), write() and mmap(). A write() notifies the peer guest through an
architecture-specific hypercall (HVC on arm/arm64, SBI ecall on RISC-V).
Co-developed-by: José Martins <jose at osyx.tech>
Signed-off-by: José Martins <jose at osyx.tech>
Co-developed-by: David Cerdeira <davidmcerdeira at osyx.tech>
Signed-off-by: David Cerdeira <davidmcerdeira at osyx.tech>
Signed-off-by: João Peixoto <jpeixoto at osyx.tech>
---
v3:
- Map the read and write regions from the two reg entries (by reg-name)
instead of parsing read-channel/write-channel offsets; read the channel id
from "bao,id"; mmap() now maps per region.
- Drop the noisy dev_info() on successful probe.
- Do the shared-memory range arithmetic in u64 to avoid a u32 overflow.
- Fix the Kconfig help-text indentation (Randy Dunlap).
- Add José's and David's Co-developed-by/Signed-off-by.
arch/arm/include/asm/bao.h | 31 ++++
arch/arm64/include/asm/bao.h | 31 ++++
arch/riscv/include/asm/bao.h | 31 ++++
drivers/virt/Kconfig | 2 +
drivers/virt/Makefile | 1 +
drivers/virt/bao/Kconfig | 3 +
drivers/virt/bao/Makefile | 3 +
drivers/virt/bao/ipcshmem/Kconfig | 10 ++
drivers/virt/bao/ipcshmem/Makefile | 3 +
drivers/virt/bao/ipcshmem/ipcshmem.c | 231 +++++++++++++++++++++++++++
10 files changed, 346 insertions(+)
create mode 100644 arch/arm/include/asm/bao.h
create mode 100644 arch/arm64/include/asm/bao.h
create mode 100644 arch/riscv/include/asm/bao.h
create mode 100644 drivers/virt/bao/Kconfig
create mode 100644 drivers/virt/bao/Makefile
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
diff --git a/arch/arm/include/asm/bao.h b/arch/arm/include/asm/bao.h
new file mode 100644
index 000000000000..ba64d1a18f91
--- /dev/null
+++ b/arch/arm/include/asm/bao.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Bao Hypervisor Hypercall Interface
+ *
+ * Copyright (c) Bao Project and Contributors. All rights reserved.
+ *
+ * Authors:
+ * João Peixoto <jpeixoto at osyx.tech>
+ * José Martins <jose at osyx.tech>
+ * David Cerdeira <davidmcerdeira at osyx.tech>
+ */
+
+#ifndef __ASM_ARM_BAO_H
+#define __ASM_ARM_BAO_H
+
+#include <linux/arm-smccc.h>
+
+static inline unsigned long bao_ipcshmem_hypercall(unsigned long hypercall_id,
+ unsigned long ipcshmem_id)
+{
+ struct arm_smccc_res res;
+
+ arm_smccc_hvc(ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, ARM_SMCCC_SMC_32,
+ ARM_SMCCC_OWNER_VENDOR_HYP,
+ hypercall_id),
+ ipcshmem_id, 0, 0, 0, 0, 0, 0, &res);
+
+ return res.a0;
+}
+
+#endif /* __ASM_ARM_BAO_H */
diff --git a/arch/arm64/include/asm/bao.h b/arch/arm64/include/asm/bao.h
new file mode 100644
index 000000000000..ab9b283168e3
--- /dev/null
+++ b/arch/arm64/include/asm/bao.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Bao Hypervisor Hypercall Interface
+ *
+ * Copyright (c) Bao Project and Contributors. All rights reserved.
+ *
+ * Authors:
+ * João Peixoto <jpeixoto at osyx.tech>
+ * José Martins <jose at osyx.tech>
+ * David Cerdeira <davidmcerdeira at osyx.tech>
+ */
+
+#ifndef __ASM_ARM64_BAO_H
+#define __ASM_ARM64_BAO_H
+
+#include <linux/arm-smccc.h>
+
+static inline unsigned long bao_ipcshmem_hypercall(unsigned long hypercall_id,
+ unsigned long ipcshmem_id)
+{
+ struct arm_smccc_res res;
+
+ arm_smccc_hvc(ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, ARM_SMCCC_SMC_64,
+ ARM_SMCCC_OWNER_VENDOR_HYP,
+ hypercall_id),
+ ipcshmem_id, 0, 0, 0, 0, 0, 0, &res);
+
+ return res.a0;
+}
+
+#endif /* __ASM_ARM64_BAO_H */
diff --git a/arch/riscv/include/asm/bao.h b/arch/riscv/include/asm/bao.h
new file mode 100644
index 000000000000..d2c79a6a4ade
--- /dev/null
+++ b/arch/riscv/include/asm/bao.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Bao Hypervisor Hypercall Interface
+ *
+ * Copyright (c) Bao Project and Contributors. All rights reserved.
+ *
+ * Authors:
+ * João Peixoto <jpeixoto at osyx.tech>
+ * José Martins <jose at osyx.tech>
+ * David Cerdeira <davidmcerdeira at osyx.tech>
+ */
+
+#ifndef __ASM_RISCV_BAO_H
+#define __ASM_RISCV_BAO_H
+
+#include <asm/sbi.h>
+
+#define BAO_SBI_EXT_ID 0x08000ba0
+
+static inline unsigned long bao_ipcshmem_hypercall(unsigned long hypercall_id,
+ unsigned long ipcshmem_id)
+{
+ struct sbiret ret;
+
+ ret = sbi_ecall(BAO_SBI_EXT_ID, hypercall_id, ipcshmem_id, 0, 0, 0, 0,
+ 0);
+
+ return ret.error;
+}
+
+#endif /* __ASM_RISCV_BAO_H */
diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
index 52eb7e4ba71f..cb98c4c52fd1 100644
--- a/drivers/virt/Kconfig
+++ b/drivers/virt/Kconfig
@@ -47,6 +47,8 @@ source "drivers/virt/nitro_enclaves/Kconfig"
source "drivers/virt/acrn/Kconfig"
+source "drivers/virt/bao/Kconfig"
+
endif
source "drivers/virt/coco/Kconfig"
diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
index f29901bd7820..623a671f8711 100644
--- a/drivers/virt/Makefile
+++ b/drivers/virt/Makefile
@@ -10,3 +10,4 @@ obj-y += vboxguest/
obj-$(CONFIG_NITRO_ENCLAVES) += nitro_enclaves/
obj-$(CONFIG_ACRN_HSM) += acrn/
obj-y += coco/
+obj-$(CONFIG_BAO_SHMEM) += bao/
diff --git a/drivers/virt/bao/Kconfig b/drivers/virt/bao/Kconfig
new file mode 100644
index 000000000000..4f7929d57475
--- /dev/null
+++ b/drivers/virt/bao/Kconfig
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+source "drivers/virt/bao/ipcshmem/Kconfig"
diff --git a/drivers/virt/bao/Makefile b/drivers/virt/bao/Makefile
new file mode 100644
index 000000000000..68f5d3f282c4
--- /dev/null
+++ b/drivers/virt/bao/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_BAO_SHMEM) += ipcshmem/
diff --git a/drivers/virt/bao/ipcshmem/Kconfig b/drivers/virt/bao/ipcshmem/Kconfig
new file mode 100644
index 000000000000..b789e5ea1264
--- /dev/null
+++ b/drivers/virt/bao/ipcshmem/Kconfig
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+config BAO_SHMEM
+ tristate "Bao hypervisor shared memory support"
+ help
+ This enables support for Bao shared memory communication.
+ It allows the kernel to interface with guests running under
+ the Bao hypervisor, providing a character device interface
+ for exchanging data through dedicated shared-memory regions.
+
+ If unsure, say N.
diff --git a/drivers/virt/bao/ipcshmem/Makefile b/drivers/virt/bao/ipcshmem/Makefile
new file mode 100644
index 000000000000..e027dcdb06aa
--- /dev/null
+++ b/drivers/virt/bao/ipcshmem/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_BAO_SHMEM) += bao.o
+bao-objs += ipcshmem.o
diff --git a/drivers/virt/bao/ipcshmem/ipcshmem.c b/drivers/virt/bao/ipcshmem/ipcshmem.c
new file mode 100644
index 000000000000..0d46d89ee788
--- /dev/null
+++ b/drivers/virt/bao/ipcshmem/ipcshmem.c
@@ -0,0 +1,231 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Bao Hypervisor IPC Through Shared-memory Driver
+ *
+ * Copyright (c) Bao Project and Contributors. All rights reserved.
+ */
+
+#include <linux/platform_device.h>
+#include <linux/miscdevice.h>
+#include <linux/of.h>
+#include <linux/mm.h>
+#include <linux/io.h>
+#include <asm/bao.h>
+
+#define BAO_IPCSHMEM_NAME_LEN 16
+
+/* IPC through shared-memory hypercall ID */
+#define BAO_IPCSHMEM_HYPERCALL_ID 0x1
+
+struct bao_ipcshmem {
+ struct miscdevice miscdev;
+ u32 id;
+ char label[BAO_IPCSHMEM_NAME_LEN];
+ void *read_base;
+ phys_addr_t read_phys;
+ size_t read_size;
+ void *write_base;
+ phys_addr_t write_phys;
+ size_t write_size;
+};
+
+static int bao_ipcshmem_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+ struct bao_ipcshmem *bao = filp->private_data;
+ unsigned long vsize = vma->vm_end - vma->vm_start;
+ unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
+ phys_addr_t region_phys;
+ size_t region_size;
+
+ if (!vsize)
+ return -EINVAL;
+
+ /*
+ * The read region is exposed at offset 0 and the write region right
+ * after it. A single mapping cannot span both regions, since they are
+ * not guaranteed to be physically contiguous.
+ */
+ if (offset < bao->read_size) {
+ region_phys = bao->read_phys;
+ region_size = bao->read_size;
+ } else if (offset < bao->read_size + bao->write_size) {
+ offset -= bao->read_size;
+ region_phys = bao->write_phys;
+ region_size = bao->write_size;
+ } else {
+ return -EINVAL;
+ }
+
+ if (vsize > region_size - offset)
+ return -EINVAL;
+
+ region_phys += offset;
+ if (!PAGE_ALIGNED(region_phys))
+ return -EINVAL;
+
+ return remap_pfn_range(vma, vma->vm_start, region_phys >> PAGE_SHIFT,
+ vsize, vma->vm_page_prot);
+}
+
+static ssize_t bao_ipcshmem_read(struct file *filp, char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct bao_ipcshmem *bao = filp->private_data;
+ size_t available;
+
+ if (*ppos >= bao->read_size)
+ return 0;
+
+ available = bao->read_size - *ppos;
+ count = min(count, available);
+
+ if (copy_to_user(buf, bao->read_base + *ppos, count))
+ return -EFAULT;
+
+ *ppos += count;
+ return count;
+}
+
+static ssize_t bao_ipcshmem_write(struct file *filp, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct bao_ipcshmem *bao = filp->private_data;
+ size_t available;
+
+ if (*ppos >= bao->write_size)
+ return 0;
+
+ available = bao->write_size - *ppos;
+ count = min(count, available);
+
+ if (copy_from_user(bao->write_base + *ppos, buf, count))
+ return -EFAULT;
+
+ *ppos += count;
+
+ /* Notify Bao hypervisor */
+ bao_ipcshmem_hypercall(BAO_IPCSHMEM_HYPERCALL_ID, bao->id);
+
+ return count;
+}
+
+static int bao_ipcshmem_open(struct inode *inode, struct file *filp)
+{
+ struct bao_ipcshmem *bao;
+
+ bao = container_of(filp->private_data, struct bao_ipcshmem, miscdev);
+ filp->private_data = bao;
+
+ return 0;
+}
+
+static int bao_ipcshmem_release(struct inode *inode, struct file *filp)
+{
+ filp->private_data = NULL;
+ return 0;
+}
+
+static const struct file_operations bao_ipcshmem_fops = {
+ .owner = THIS_MODULE,
+ .read = bao_ipcshmem_read,
+ .write = bao_ipcshmem_write,
+ .mmap = bao_ipcshmem_mmap,
+ .open = bao_ipcshmem_open,
+ .release = bao_ipcshmem_release,
+};
+
+static int bao_ipcshmem_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct device_node *np = dev->of_node;
+ struct resource *read_res;
+ struct resource *write_res;
+ struct bao_ipcshmem *bao;
+ u32 id;
+ int ret;
+
+ read_res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "read");
+ if (!read_res) {
+ dev_err(dev, "missing 'read' shared memory region\n");
+ return -ENODEV;
+ }
+
+ write_res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "write");
+ if (!write_res) {
+ dev_err(dev, "missing 'write' shared memory region\n");
+ return -ENODEV;
+ }
+
+ ret = of_property_read_u32(np, "bao,id", &id);
+ if (ret) {
+ dev_err(dev, "missing or invalid 'bao,id' property\n");
+ return ret;
+ }
+
+ bao = devm_kzalloc(dev, sizeof(*bao), GFP_KERNEL);
+ if (!bao)
+ return -ENOMEM;
+
+ bao->read_base = devm_memremap(dev, read_res->start,
+ resource_size(read_res), MEMREMAP_WB);
+ if (IS_ERR(bao->read_base))
+ return PTR_ERR(bao->read_base);
+
+ bao->write_base = devm_memremap(dev, write_res->start,
+ resource_size(write_res), MEMREMAP_WB);
+ if (IS_ERR(bao->write_base))
+ return PTR_ERR(bao->write_base);
+
+ bao->id = id;
+ bao->read_phys = read_res->start;
+ bao->read_size = resource_size(read_res);
+ bao->write_phys = write_res->start;
+ bao->write_size = resource_size(write_res);
+
+ scnprintf(bao->label, BAO_IPCSHMEM_NAME_LEN, "baoipc%u", id);
+
+ bao->miscdev.minor = MISC_DYNAMIC_MINOR;
+ bao->miscdev.name = bao->label;
+ bao->miscdev.fops = &bao_ipcshmem_fops;
+ bao->miscdev.parent = dev;
+
+ ret = misc_register(&bao->miscdev);
+ if (ret) {
+ dev_err(dev, "failed to register misc device: %d\n", ret);
+ return ret;
+ }
+
+ platform_set_drvdata(pdev, bao);
+
+ return 0;
+}
+
+static void bao_ipcshmem_remove(struct platform_device *pdev)
+{
+ struct bao_ipcshmem *bao = platform_get_drvdata(pdev);
+
+ misc_deregister(&bao->miscdev);
+}
+
+static const struct of_device_id of_bao_ipcshmem_match[] = {
+ { .compatible = "bao,ipcshmem" },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, of_bao_ipcshmem_match);
+
+static struct platform_driver bao_ipcshmem_driver = {
+ .probe = bao_ipcshmem_probe,
+ .remove = bao_ipcshmem_remove,
+ .driver = {
+ .name = "baoipc",
+ .of_match_table = of_bao_ipcshmem_match,
+ },
+};
+
+module_platform_driver(bao_ipcshmem_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("David Cerdeira <davidmcerdeira at osyx.tech>");
+MODULE_AUTHOR("José Martins <jose at osyx.tech>");
+MODULE_AUTHOR("João Peixoto <jpeixoto at osyx.tech>");
+MODULE_DESCRIPTION("Bao Hypervisor IPC Through Shared-memory Driver");
--
2.43.0
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