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

From: Marcelo Tosatti <mtosatti@redhat.com>
To: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Dustin Kirkland <kirkland@canonical.com>,
	Mark McLoughlin <markmc@redhat.com>,
	qemu-devel@nongnu.org, kvm@vger.kernel.org,
	Glauber Costa <glommer@gmail.com>
Subject: Re: [Qemu-devel] Re: [PATCH] qemu-kvm: fix segfault when running kvm without /dev/kvm, falling back to non-accelerated mode
Date: Fri, 4 Sep 2009 18:46:23 -0300	[thread overview]
Message-ID: <20090904214623.GA10196@amt.cnet> (raw)
In-Reply-To: <20090904183925.63b0b5f7@doriath>

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) {
