Re: [Qemu-devel] Re: [PATCH] qemu-kvm: fix segfault when running kvm without /dev/kvm, falling back to non-accelerated mode

Marcelo Tosatti
2009-09-04T21:47:00Z

On Fri, Sep 04, 2009 at 06:39:25PM -0300, Luiz Capitulino wrote:
> > Sure, Marcelo. It's attached.
> >
> > I tested it, and it still does avoid the segfault.
> >
> > Luiz, could you re-test this patch on your side too?
>
> I'm getting rejections, are you sure it's against upstream?

Its againts 0.11-stable branch. Try this against master:

qemu-kvm segfaults on systems without access to /dev/kvm.
The global kvm_allowed is being set too late in vl.c.

This patch moves the kvm initialization a bit higher in the
vl.c main, just after the daemonize fork.

This fix is intended to be a short term solution, solving the
segfaults.

In the longer term, the suggested approach requires a bit more
development and testing:
* If no arg given => try kvm, try kqemu, try tcg
* If --accelmode arg given => try $arg, and fail if unavailable

Signed-off-by: Dustin Kirkland <kirkland@canonical.com>

diff --git a/vl.c b/vl.c
index 9f03d85..3485ce6 100644
--- a/vl.c
+++ b/vl.c
@@ -5823,6 +5823,20 @@ int main(int argc, char **argv, char **envp)
signal(SIGTTIN, SIG_IGN);
}

+ if (kvm_enabled()) {
+ int ret;
+
+ ret = kvm_init(smp_cpus);
+ if (ret < 0) {
+#if defined(KVM_UPSTREAM) || defined(NO_CPU_EMULATION)
+ fprintf(stderr, "failed to initialize KVM\n");
+ exit(1);
+#endif
+ fprintf(stderr, "Could not initialize KVM, will disable KVM support\n");
+ kvm_allowed = 0;
+ }
+ }
+
if (pid_file && qemu_create_pidfile(pid_file) != 0) {
if (daemonize) {
uint8_t status = 1;
@@ -5983,20 +5997,6 @@ int main(int argc, char **argv, char **envp)
}
}

- if (kvm_enabled()) {
- int ret;
-
- ret = kvm_init(smp_cpus);
- if (ret < 0) {
-#if defined(KVM_UPSTREAM) || defined(NO_CPU_EMULATION)
- fprintf(stderr, "failed to initialize KVM\n");
- exit(1);
-#endif
- fprintf(stderr, "Could not initialize KVM, will disable KVM support\n");
- kvm_allowed = 0;
- }
- }
-
if (monitor_device) {
monitor_hd = qemu_chr_open("monitor", monitor_device, NULL);
if (!monitor_hd) {