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Commit d6d9ef6b authored by Florent Gluck's avatar Florent Gluck
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Added new slide about err vs errx, minor improvements throughout the slides

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course/02-KVM.md
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......@@ -168,20 +168,30 @@ pandoc-latex-fontsize:
\vspace{.3cm}
```{.c .verysmall}
int kvmfd = open("/dev/kvm", O_RDWR | O_CLOEXEC);
if (kvmfd < 0) err(1, "%s", "/dev/kvm");
if (kvmfd < 0) err(1, "Failed opening kvm device: ");
int version = ioctl(kvmfd, KVM_GET_API_VERSION, NULL);
if (version < 0) err(1, "KVM_GET_API_VERSION");
if (version != KVM_API_VERSION) err(1, "Unsupported version of the KVM API");
if (version < 0) err(1, "KVM_GET_API_VERSION failed: ");
if (version != KVM_API_VERSION) errx(1, "Error: KVM_GET_API_VERSION %d, expected %d!", version, KVM_API_VERSION);
```
[//]: # ----------------------------------------------------------------
## Abort handling: err vs errx
- Both `err` and `errx` functions print an error message to `stderr` and abort the current process
- `err` must be used when the function that fails sets `errno` (typically a system call)
- `err` appends an error message (based on `errno`) to the text passed in argument
- `errx` must be used when the function that fails does not set `errno`
- Both functions accept variable parameters (like `printf`)
[//]: # ----------------------------------------------------------------
## (2) Create a VM
- To obtain a file descriptor (here, `vmfd`) on a newly created VM:
```{.c .verysmall}
int vmfd = ioctl(kvmfd, KVM_CREATE_VM, 0);
if (vmfd < 0) err(1, "KVM_CREATE_VM");
#define MACHINE_TYPE 0
int vmfd = ioctl(kvmfd, KVM_CREATE_VM, MACHINE_TYPE);
if (vmfd < 0) err(1, "Error: KVM_CREATE_VM failed: ");
```
- This file descriptor allows us to:
- defines the VM's memory address space
......@@ -206,7 +216,7 @@ pandoc-latex-fontsize:
// Alloc 4KB for the guest
u_int ram_size = 4096;
uint8_t *mem = mmap(NULL, ram_size, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
if (!mem) err(1, "Allocating guest memory");
if (!mem) err(1, "Error: failed allocating guest memory: ");
```
[//]: # ----------------------------------------------------------------
......@@ -224,7 +234,7 @@ pandoc-latex-fontsize:
.userspace_addr = (uint64_t)mem,
.flags = 0
};
if (ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, &memreg) < 0) err(1, "KVM_SET_USER_MEMORY_REGION");
if (ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, &memreg) < 0) err(1, "Error: KVM_SET_USER_MEMORY_REGION: ");
```
<!--
......@@ -245,7 +255,7 @@ pandoc-latex-fontsize:
.userspace_addr = (uint64_t)mmio,
.flags = KVM_MEM_READONLY // Mandatory for MMIO!
};
if (ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, &memreg) < 0) err(1, "KVM_SET_USER_MEMORY_REGION");
if (ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, &memreg) < 0) err(1, "Error: KVM_SET_USER_MEMORY_REGION: ");
```
-->
......@@ -269,14 +279,14 @@ pandoc-latex-fontsize:
\vspace{.3cm}
```{.c .tiny}
int vcpufd = ioctl(vmfd, KVM_CREATE_VCPU, 0);
if (vcpufd < 0) err(1, "KVM_CREATE_VCPU");
if (vcpufd < 0) err(1, "Error: KVM_CREATE_VCPU: ");
int vcpu_mmap_sz = ioctl(kvmfd, KVM_GET_VCPU_MMAP_SIZE, NULL);
if (vcpu_mmap_sz < 0) err(1, "KVM_GET_VCPU_MMAP_SIZE");
if (vcpu_mmap_sz < sizeof(struct kvm_run)) err(1, "KVM_GET_VCPU_MMAP_SIZE unexpectedly small");
if (vcpu_mmap_sz < 0) err(1, "Error: KVM_GET_VCPU_MMAP_SIZE: ");
if (vcpu_mmap_sz < sizeof(struct kvm_run)) err(1, "Error: KVM_GET_VCPU_MMAP_SIZE unexpectedly small: ");
struct kvm_run *run = mmap(NULL, vcpu_mmap_sz, PROT_READ | PROT_WRITE, MAP_SHARED, vcpufd, 0);
if (!run) err(1, "mmap vcpu");
if (!run) err(1, "Error: Failed to mmap vCPU: ");
```
[//]: # ----------------------------------------------------------------
......@@ -286,12 +296,12 @@ pandoc-latex-fontsize:
\vspace{.3cm}
```{.c .verysmall}
struct kvm_sregs sregs;
if (ioctl(vcpufd, KVM_GET_SREGS, &sregs) < 0) err(1, "KVM_GET_SREGS");
if (ioctl(vcpufd, KVM_GET_SREGS, &sregs) < 0) err(1, "Error: KVM_GET_SREGS: ");
sregs.cs.base = 0; sregs.cs.selector = 0;
sregs.ds.base = 0; sregs.ds.selector = 0;
sregs.es.base = 0; sregs.es.selector = 0;
sregs.ss.base = 0; sregs.ss.selector = 0;
if (ioctl(vcpufd, KVM_SET_SREGS, &sregs) < 0) err(1, "KVM_SET_SREGS");
if (ioctl(vcpufd, KVM_SET_SREGS, &sregs) < 0) err(1, "Error: KVM_SET_SREGS: ");
```
[//]: # ----------------------------------------------------------------
......@@ -307,7 +317,7 @@ pandoc-latex-fontsize:
regs.rip = 0;
regs.rsp = ram_size;
regs.rflags = 0x2;
if (ioctl(vcpufd, KVM_SET_REGS, &regs) < 0) err(1, "KVM_SET_REGS");
if (ioctl(vcpufd, KVM_SET_REGS, &regs) < 0) err(1, "Error: KVM_SET_REGS: ");
```
[//]: # ----------------------------------------------------------------
......@@ -322,7 +332,7 @@ pandoc-latex-fontsize:
bool done = false;
while (!done) {
// Runs the vCPU until encoutering a VM_EXIT (blocking call)
if (ioctl(vcpufd, KVM_RUN, NULL) < 0) err(1, "KVM_RUN");
if (ioctl(vcpufd, KVM_RUN, NULL) < 0) err(1, "Error: KVM_RUN: ");
switch (run->exit_reason) { // See struct kvm_run in "(6) Create a vCPU"
case KVM_EXIT_IO: // Encountered a PMIO VMexit
break; // This VMexit should be handled here...
......@@ -1097,11 +1107,12 @@ outb(0x3C5, 0x0F);
## Why hardware interrupts?
- To avoid constantly polling devices
- Polling must be avoided:
- Polling should be avoided:
- polling frequently: low latency, but high CPU usage
- polling infrequently: low CPU usage, but high latency
- To handle timers
- A timer offers a time base independent of the CPU frequency
- necessary to mesure time accurately
- necessary to implement `sleep` or similar functionalities
[//]: # ----------------------------------------------------------------
......@@ -1158,11 +1169,13 @@ A Programmable Interrupt Controller (PIC) is created by using the following `ioc
\vspace{.3cm}
```{.verysmall .c}
if (ioctl(vmfd, KVM_CREATE_IRQCHIP, 0) < 0) {
if (ioctl(vmfd, KVM_CREATE_IRQCHIP, NULL) < 0) {
// Error...
}
```
Make sure to create it **\textcolor{myred}{before}** creating any vCPU!
[//]: # ----------------------------------------------------------------
## Injection VMM side: (2) configure virtual PIC
......@@ -1231,7 +1244,7 @@ Create a file descriptor for event notification by using the `eventfd` function:
// Create a file descriptor for event (hardware interrupts) notification
int fd = eventfd(0, 0);
if (fd == -1) {
err(1, "eventfd failed");
err(1, "eventfd failed: ");
}
```
......@@ -1250,7 +1263,7 @@ if (fd == -1) {
};
if (ioctl(vm->vmfd, KVM_IRQFD, &irqfd) < 0) {
err(1, "KVM_IRQFD error");
err(1, "KVM_IRQFD error: ");
}
```
......@@ -1276,7 +1289,7 @@ Perform the same steps as on a real physical system[^4]:
- implement ISRs for all potential hardware interrupts that may be triggered
1. Unmask hardware interrupts so that they will be received
\textcolor{myred}{Receiving a hardware interrupts for which there is no properly initialized IVT entry will result in a shutdown/reboot of the guest (as it would on a physical machine)}
\textcolor{myred}{Receiving a hardware interrupts for which there is no properly initialized IVT entry will result in a reboot of the guest (as it would on a physical machine)}
[^4]: \scriptsize With one exception: in the ISR, no need to send an EOI command to the PIC
......
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