[PATCH 09/16] KVM: device: Add test device
From: Charlie Jenkins via B4 Relay
Date: Wed Apr 08 2026 - 00:48:32 EST
From: Charlie Jenkins <thecharlesjenkins@xxxxxxxxx>
Create a KVM test device to help verify mmio reads and write emulation.
This is a simple device that will store the data in a buffer on writes
and echo back that stored data on a read.
Signed-off-by: Charlie Jenkins <thecharlesjenkins@xxxxxxxxx>
---
include/uapi/linux/kvm.h | 2 +
lib/Kconfig.debug | 6 +++
virt/kvm/Kconfig.debug | 16 ++++++++
virt/kvm/Makefile.kvm | 1 +
virt/kvm/kvm_main.c | 8 ++++
virt/kvm/mmio_test.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++
virt/kvm/mmio_test.h | 18 +++++++++
7 files changed, 146 insertions(+)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index dddb781b0507..9e2918614246 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1209,6 +1209,8 @@ enum kvm_device_type {
#define KVM_DEV_TYPE_LOONGARCH_EIOINTC KVM_DEV_TYPE_LOONGARCH_EIOINTC
KVM_DEV_TYPE_LOONGARCH_PCHPIC,
#define KVM_DEV_TYPE_LOONGARCH_PCHPIC KVM_DEV_TYPE_LOONGARCH_PCHPIC
+ KVM_DEV_TYPE_TEST,
+#define KVM_DEV_TYPE_TEST KVM_DEV_TYPE_TEST
KVM_DEV_TYPE_MAX,
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ba36939fda79..7a4a23d1fc9e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -717,6 +717,12 @@ source "net/Kconfig.debug"
endmenu # "Networking Debugging"
+menu "KVM Debugging"
+
+source "virt/kvm/Kconfig.debug"
+
+endmenu # "KVM Debugging"
+
menu "Memory Debugging"
source "mm/Kconfig.debug"
diff --git a/virt/kvm/Kconfig.debug b/virt/kvm/Kconfig.debug
new file mode 100644
index 000000000000..d24709f5bcbf
--- /dev/null
+++ b/virt/kvm/Kconfig.debug
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+config KVM_MMIO_TEST
+ bool "Enable kvm mmio testing"
+ depends on KVM
+ depends on KVM_MMIO
+ default n
+ help
+ Enable testing for kvm mmio. This is a test-only mmio device that
+ stores writes in a buffer and returns the buffered data on a read.
+
+ This is useful for testing the kvm mmio emulation code. Enabling
+ this does not run any tests, just builds in the support for the test
+ device into the kernel.
+
+ If unsure, say N.
diff --git a/virt/kvm/Makefile.kvm b/virt/kvm/Makefile.kvm
index d047d4cf58c9..bd4da8c23923 100644
--- a/virt/kvm/Makefile.kvm
+++ b/virt/kvm/Makefile.kvm
@@ -8,6 +8,7 @@ KVM ?= ../../../virt/kvm
kvm-y := $(KVM)/kvm_main.o $(KVM)/eventfd.o $(KVM)/binary_stats.o
kvm-$(CONFIG_KVM_VFIO) += $(KVM)/vfio.o
kvm-$(CONFIG_KVM_MMIO) += $(KVM)/coalesced_mmio.o
+kvm-$(CONFIG_KVM_MMIO_TEST) += $(KVM)/mmio_test.o
kvm-$(CONFIG_KVM_ASYNC_PF) += $(KVM)/async_pf.o
kvm-$(CONFIG_HAVE_KVM_IRQ_ROUTING) += $(KVM)/irqchip.o
kvm-$(CONFIG_HAVE_KVM_DIRTY_RING) += $(KVM)/dirty_ring.o
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5fcd401a5897..a0b143e71560 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -59,6 +59,7 @@
#include "async_pf.h"
#include "kvm_mm.h"
#include "vfio.h"
+#include "mmio_test.h"
#include <trace/events/ipi.h>
@@ -6528,6 +6529,10 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
if (WARN_ON_ONCE(r))
goto err_vfio;
+ r = kvm_mmio_test_ops_init();
+ if (WARN_ON_ONCE(r))
+ goto err_mmio_test;
+
r = kvm_gmem_init(module);
if (r)
goto err_gmem;
@@ -6555,6 +6560,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
err_gmem:
kvm_vfio_ops_exit();
err_vfio:
+ kvm_mmio_test_ops_exit();
+err_mmio_test:
kvm_async_pf_deinit();
err_async_pf:
kvm_irqfd_exit();
@@ -6585,6 +6592,7 @@ void kvm_exit(void)
free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
kmem_cache_destroy(kvm_vcpu_cache);
kvm_gmem_exit();
+ kvm_mmio_test_ops_exit();
kvm_vfio_ops_exit();
kvm_async_pf_deinit();
kvm_irqfd_exit();
diff --git a/virt/kvm/mmio_test.c b/virt/kvm/mmio_test.c
new file mode 100644
index 000000000000..fa84c2b4c5fc
--- /dev/null
+++ b/virt/kvm/mmio_test.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * mmio_test.c - Kernel module side for testing the KVM riscv mmio functionality.
+ */
+
+#include <linux/kvm_host.h>
+
+#include <kvm/iodev.h>
+#include "mmio_test.h"
+
+struct mmio_test {
+ struct kvm *kvm;
+ struct kvm_io_device dev;
+ unsigned long start;
+ unsigned long size;
+ char cache[16];
+};
+
+static struct mmio_test *kvm_to_mmio_test_dev(const struct kvm_io_device *dev)
+{
+ return container_of(dev, struct mmio_test, dev);
+}
+
+static int mmio_read(struct kvm_vcpu *vcpu, struct kvm_io_device *dev,
+ gpa_t addr, int len, void *val)
+{
+ struct mmio_test *mmio_test = kvm_to_mmio_test_dev(dev);
+
+ if ((addr - mmio_test->start) >= mmio_test->size)
+ return -1;
+
+ /* Write back cached value */
+ memcpy(val, &mmio_test->cache[(addr - mmio_test->start)], len);
+ return 0;
+}
+
+static int mmio_write(struct kvm_vcpu *vcpu, struct kvm_io_device *dev,
+ gpa_t addr, int len, const void *val)
+{
+ struct mmio_test *mmio_test = kvm_to_mmio_test_dev(dev);
+
+ if ((addr - mmio_test->start) >= mmio_test->size)
+ return -1;
+
+ /* Cache value */
+ memcpy(&mmio_test->cache[(addr - mmio_test->start)], val, len);
+ return 0;
+}
+
+static const struct kvm_io_device_ops mmio_ops = {
+ .read = mmio_read,
+ .write = mmio_write,
+};
+
+static int mmio_test_create(struct kvm_device *dev, u32 type)
+{
+ struct mmio_test *mmio_test;
+
+ mmio_test = kzalloc(sizeof(*mmio_test), GFP_KERNEL);
+ if (!mmio_test)
+ return -ENOMEM;
+
+ mmio_test->start = 0x20000000;
+ mmio_test->size = 0x16;
+
+ dev->private = mmio_test;
+
+ kvm_iodevice_init(&mmio_test->dev, &mmio_ops);
+ kvm_io_bus_register_dev(dev->kvm, KVM_MMIO_BUS, mmio_test->start,
+ mmio_test->size, &mmio_test->dev);
+
+ return 0;
+}
+
+static void mmio_test_release(struct kvm_device *dev)
+{
+ kfree(dev->private);
+}
+
+struct kvm_device_ops kvm_riscv_mmio_test_device_ops = {
+ .name = "kvm-riscv-mmio_test",
+ .create = mmio_test_create,
+ .release = mmio_test_release,
+};
+
+int kvm_mmio_test_ops_init(void)
+{
+ return kvm_register_device_ops(&kvm_riscv_mmio_test_device_ops,
+ KVM_DEV_TYPE_TEST);
+}
+
+void kvm_mmio_test_ops_exit(void)
+{
+ kvm_unregister_device_ops(KVM_DEV_TYPE_TEST);
+}
diff --git a/virt/kvm/mmio_test.h b/virt/kvm/mmio_test.h
new file mode 100644
index 000000000000..49a6e900eec9
--- /dev/null
+++ b/virt/kvm/mmio_test.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __KVM_MMIO_TEST_H
+#define __KVM_MMIO_TEST_H
+
+#ifdef CONFIG_KVM_MMIO_TEST
+int kvm_mmio_test_ops_init(void);
+void kvm_mmio_test_ops_exit(void);
+#else
+static inline int kvm_mmio_test_ops_init(void)
+{
+ return 0;
+}
+static inline void kvm_mmio_test_ops_exit(void)
+{
+}
+#endif
+
+#endif
--
2.52.0