Using the KVM API Arm64
Port code on using the KVM API (https://lwn.net/Articles/658511/) to
Arm64.
This uses the API to go through the whole life cycle of a VM in a
couple of screens.
Signed-off-by: Fuad Tabba <tabba@google.com>
diff --git a/kvmtest/kvmtest-arm64.c b/kvmtest/kvmtest-arm64.c
index dd4c714..4363ff5 100644
--- a/kvmtest/kvmtest-arm64.c
+++ b/kvmtest/kvmtest-arm64.c
@@ -1,3 +1,14 @@
+/*
+ *
+ * This is an Arm64 port of the x86 code accompanying "Using the KVM API"
+ * (https://lwn.net/Articles/658511/).
+ *
+ * Original x86 code in the file kvmtest.c and https://lwn.net/Articles/658512/.
+ *
+ * Copyright (C) 2020 Google LLC
+ * Author: Fuad Tabba <tabba@google.com>
+ */
+
/* Sample code for /dev/kvm API
*
* Copyright (c) 2015 Intel Corporation
@@ -36,59 +47,69 @@
int main(void)
{
int kvm, vmfd, vcpufd, ret;
+
+ /* Add x0 to x1 and outputs the result to MMIO at address in x2. */
const uint8_t code[] = {
- 0xba, 0xf8, 0x03, /* mov $0x3f8, %dx */
- 0x00, 0xd8, /* add %bl, %al */
- 0x04, '0', /* add $'0', %al */
- 0xee, /* out %al, (%dx) */
- 0xb0, '\n', /* mov $'\n', %al */
- 0xee, /* out %al, (%dx) */
- 0xf4, /* hlt */
+ 0x20, 0x00, 0x00, 0x8b, /* add x0, x1, x0 */
+ 0x40, 0x00, 0x00, 0xf9, /* str x0, [x2]*/
+ 0x00, 0x00, 0x20, 0xd4, /* brk */
};
- uint8_t *mem;
- struct kvm_sregs sregs;
+ const uint64_t code_address = 0x1000;
+ const uint64_t mmio_address = 0x2000;
+ uint8_t *mem_code = NULL;
size_t mmap_size;
- struct kvm_run *run;
+ struct kvm_run *run = NULL;
kvm = open("/dev/kvm", O_RDWR | O_CLOEXEC);
- if (kvm == -1)
+ if (kvm < 0)
err(1, "/dev/kvm");
- /* Make sure we have the stable version of the API */
+ /* Ensure this is the stable version of the KVM API (defined as 12) */
ret = ioctl(kvm, KVM_GET_API_VERSION, NULL);
- if (ret == -1)
+ if (ret < 0)
err(1, "KVM_GET_API_VERSION");
if (ret != 12)
errx(1, "KVM_GET_API_VERSION %d, expected 12", ret);
vmfd = ioctl(kvm, KVM_CREATE_VM, (unsigned long)0);
- if (vmfd == -1)
+ if (vmfd < 0)
err(1, "KVM_CREATE_VM");
/* Allocate one aligned page of guest memory to hold the code. */
- mem = mmap(NULL, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
- if (!mem)
+ mem_code = mmap(NULL, 0x1000,
+ PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+ if (!mem_code)
err(1, "allocating guest memory");
- memcpy(mem, code, sizeof(code));
+ memcpy(mem_code, code, sizeof(code));
- /* Map it to the second page frame (to avoid the real-mode IDT at 0). */
+ /* Map code memory to the second page frame. */
struct kvm_userspace_memory_region region = {
.slot = 0,
- .guest_phys_addr = 0x1000,
+ .guest_phys_addr = code_address,
.memory_size = 0x1000,
- .userspace_addr = (uint64_t)mem,
+ .userspace_addr = (uint64_t)mem_code,
};
ret = ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, ®ion);
- if (ret == -1)
+ if (ret < 0)
err(1, "KVM_SET_USER_MEMORY_REGION");
+ /* Use third page frame of guest memory to simulate MMIO. */
+ region.flags = KVM_MEM_READONLY; /* triggers KVM_EXIT_MEMIO on write */
+ region.slot = 1;
+ region.guest_phys_addr = mmio_address;
+ region.userspace_addr = 0ULL;
+ ret = ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, ®ion);
+ if (ret < 0)
+ err(1, "KVM_SET_USER_MEMORY_REGION");
+
+ /* Create one CPU to run in the VM. */
vcpufd = ioctl(vmfd, KVM_CREATE_VCPU, (unsigned long)0);
- if (vcpufd == -1)
+ if (vcpufd < 0)
err(1, "KVM_CREATE_VCPU");
/* Map the shared kvm_run structure and following data. */
ret = ioctl(kvm, KVM_GET_VCPU_MMAP_SIZE, NULL);
- if (ret == -1)
+ if (ret < 0)
err(1, "KVM_GET_VCPU_MMAP_SIZE");
mmap_size = ret;
if (mmap_size < sizeof(*run))
@@ -97,48 +118,78 @@
if (!run)
err(1, "mmap vcpu");
- /* Initialize CS to point at 0, via a read-modify-write of sregs. */
- ret = ioctl(vcpufd, KVM_GET_SREGS, &sregs);
- if (ret == -1)
- err(1, "KVM_GET_SREGS");
- sregs.cs.base = 0;
- sregs.cs.selector = 0;
- ret = ioctl(vcpufd, KVM_SET_SREGS, &sregs);
- if (ret == -1)
- err(1, "KVM_SET_SREGS");
+ /* Query KVM for preferred CPU target type that can be emulated. */
+ struct kvm_vcpu_init vcpu_init;
+ ret = ioctl(vmfd, KVM_ARM_PREFERRED_TARGET, &vcpu_init);
+ if (ret < 0)
+ err(1, "KVM_PREFERRED_TARGET");
- /* Initialize registers: instruction pointer for our code, addends, and
- * initial flags required by x86 architecture. */
- struct kvm_regs regs = {
- .rip = 0x1000,
- .rax = 2,
- .rbx = 2,
- .rflags = 0x2,
+ /* Initialize VCPU with the preferred type obtained above. */
+ ret = ioctl(vcpufd, KVM_ARM_VCPU_INIT, &vcpu_init);
+ if (ret < 0)
+ err(1, "KVM_ARM_VCPU_INIT");
+
+ /* Prepare the kvm_one_reg structure to use for populating registers. */
+ uint64_t reg_data;
+ struct kvm_one_reg reg;
+ reg.addr = (__u64) ®_data;
+
+ // Initialize input registers (x0 and x1) to 2.
+ reg_data = 2;
+ reg.id = 0x6030000000100000; // x0 id
+ ret = ioctl(vcpufd, KVM_SET_ONE_REG, ®);
+ if (ret != 0)
+ err(1, "KVM_SET_ONE_REG");
+ reg.id = 0x6030000000100002; // x1 id
+ ret = ioctl(vcpufd, KVM_SET_ONE_REG, ®);
+ if (ret != 0)
+ err(1, "KVM_SET_ONE_REG");
+
+ // Initialize x3 to point to the simulated MMIO region.
+ reg.id = 0x6030000000100004; // x3 id
+ reg_data = mmio_address;
+ ret = ioctl(vcpufd, KVM_SET_ONE_REG, ®);
+ if (ret != 0)
+ err(1, "KVM_SET_ONE_REG");
+
+ // Initialize the PC to point to the start of the code.
+ reg.id = 0x6030000000100040; // pc id
+ reg_data = code_address;
+ ret = ioctl(vcpufd, KVM_SET_ONE_REG, ®);
+ if (ret != 0)
+ err(1, "KVM_SET_ONE_REG");
+
+ // Enable debug so that brk instruction would exit KVM_RUN (KVM_EXIT_DEBUG).
+ struct kvm_guest_debug debug = {
+ .control = KVM_GUESTDBG_ENABLE,
};
- ret = ioctl(vcpufd, KVM_SET_REGS, ®s);
- if (ret == -1)
- err(1, "KVM_SET_REGS");
+ ret = ioctl(vcpufd, KVM_SET_GUEST_DEBUG, &debug);
+ if (ret < 0)
+ err(1, "KVM_SET_GUEST_DEBUG");
/* Repeatedly run code and handle VM exits. */
- while (1) {
+ for (;;) {
ret = ioctl(vcpufd, KVM_RUN, NULL);
- if (ret == -1)
+ if (ret < 0)
err(1, "KVM_RUN");
switch (run->exit_reason) {
- case KVM_EXIT_HLT:
- puts("KVM_EXIT_HLT");
+ case KVM_EXIT_DEBUG:
+ puts("KVM_EXIT_DEBUG");
return 0;
- case KVM_EXIT_IO:
- if (run->io.direction == KVM_EXIT_IO_OUT && run->io.size == 1 && run->io.port == 0x3f8 && run->io.count == 1)
- putchar(*(((char *)run) + run->io.data_offset));
- else
- errx(1, "unhandled KVM_EXIT_IO");
+ case KVM_EXIT_MMIO:
+ {
+ uint64_t payload = *(uint64_t*)(run->mmio.data); /* sorry */
+ printf("KVM_EXIT_MMIO: addr = 0x%llx, len = %u, is_write = %u, data = 0x%08llx\n",
+ run->mmio.phys_addr, run->mmio.len, run->mmio.is_write,
+ payload);
break;
+ }
case KVM_EXIT_FAIL_ENTRY:
errx(1, "KVM_EXIT_FAIL_ENTRY: hardware_entry_failure_reason = 0x%llx",
(unsigned long long)run->fail_entry.hardware_entry_failure_reason);
case KVM_EXIT_INTERNAL_ERROR:
- errx(1, "KVM_EXIT_INTERNAL_ERROR: suberror = 0x%x", run->internal.suberror);
+ errx(1, "KVM_EXIT_INTERNAL_ERROR: suberror = 0x%x",
+ run->internal.suberror);
default:
errx(1, "exit_reason = 0x%x", run->exit_reason);
}
