Re: [PATCH] KVM: Fix kvm_irqfd_init initialization

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, May 07, 2013 at 05:54:20PM +0200, Cornelia Huck wrote:
> On Tue,  7 May 2013 22:54:16 +0800
> Asias He <asias@redhat.com> wrote:
> 
> > In commit a0f155e96 'KVM: Initialize irqfd from kvm_init()', when
> > kvm_init() is called the second time (e.g kvm-amd.ko and kvm-intel.ko),
> > kvm_arch_init() will fail with -EEXIST, then kvm_irqfd_exit() will be
> > called on the error handling path. This way, the kvm_irqfd system will
> > not be ready.
> 
> Since we can't have the initialization as kvm module init function
> without forcing everyone to split modules, this is probably the best
> way to handle this.
> 
> Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>

Right. And please add a comment. Something like
/*
 * kvm_arch_init makes sure there's at most one caller
 * for architectures that support multiple implementations,
 * like intel and amd on x86.
 * Must be called first to avoid creating conflicts
 * in case kvm is already setup for another implementation.
*/

> > 
> > This patch fix the following:
> > 
> > BUG: unable to handle kernel NULL pointer dereference at           (null)
> > IP: [<ffffffff81c0721e>] _raw_spin_lock+0xe/0x30
> > PGD 0
> > Oops: 0002 [#1] SMP
> > Modules linked in: vhost_net
> > CPU 6
> > Pid: 4257, comm: qemu-system-x86 Not tainted 3.9.0-rc3+ #757 Dell Inc. OptiPlex 790/0V5HMK
> > RIP: 0010:[<ffffffff81c0721e>]  [<ffffffff81c0721e>] _raw_spin_lock+0xe/0x30
> > RSP: 0018:ffff880221721cc8  EFLAGS: 00010046
> > RAX: 0000000000000100 RBX: ffff88022dcc003f RCX: ffff880221734950
> > RDX: ffff8802208f6ca8 RSI: 000000007fffffff RDI: 0000000000000000
> > RBP: ffff880221721cc8 R08: 0000000000000002 R09: 0000000000000002
> > R10: 00007f7fd01087e0 R11: 0000000000000246 R12: ffff8802208f6ca8
> > R13: 0000000000000080 R14: ffff880223e2a900 R15: 0000000000000000
> > FS:  00007f7fd38488e0(0000) GS:ffff88022dcc0000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000000000000 CR3: 000000022309f000 CR4: 00000000000427e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > Process qemu-system-x86 (pid: 4257, threadinfo ffff880221720000, task ffff880222bd5640)
> > Stack:
> >  ffff880221721d08 ffffffff810ac5c5 ffff88022431dc00 0000000000000086
> >  0000000000000080 ffff880223e2a900 ffff8802208f6ca8 0000000000000000
> >  ffff880221721d48 ffffffff810ac8fe 0000000000000000 ffff880221734000
> > Call Trace:
> >  [<ffffffff810ac5c5>] __queue_work+0x45/0x2d0
> >  [<ffffffff810ac8fe>] queue_work_on+0x8e/0xa0
> >  [<ffffffff810ac949>] queue_work+0x19/0x20
> >  [<ffffffff81009b6b>] irqfd_deactivate+0x4b/0x60
> >  [<ffffffff8100a69d>] kvm_irqfd+0x39d/0x580
> >  [<ffffffff81007a27>] kvm_vm_ioctl+0x207/0x5b0
> >  [<ffffffff810c9545>] ? update_curr+0xf5/0x180
> >  [<ffffffff811b66e8>] do_vfs_ioctl+0x98/0x550
> >  [<ffffffff810c1f5e>] ? finish_task_switch+0x4e/0xe0
> >  [<ffffffff81c054aa>] ? __schedule+0x2ea/0x710
> >  [<ffffffff811b6bf7>] sys_ioctl+0x57/0x90
> >  [<ffffffff8140ae9e>] ? trace_hardirqs_on_thunk+0x3a/0x3c
> >  [<ffffffff81c0f602>] system_call_fastpath+0x16/0x1b
> > Code: c1 ea 08 38 c2 74 0f 66 0f 1f 44 00 00 f3 90 0f b6 03 38 c2 75 f7 48 83 c4 08 5b c9 c3 55 48 89 e5 66 66 66 66 90 b8 00 01 00 00 <f0> 66 0f c1 07 89 c2 66 c1 ea 08 38 c2 74 0c 0f 1f 00 f3 90 0f
> > RIP  [<ffffffff81c0721e>] _raw_spin_lock+0xe/0x30
> > RSP <ffff880221721cc8>
> > CR2: 0000000000000000
> > ---[ end trace 13fb1e4b6e5ab21f ]---
> > 
> > Signed-off-by: Asias He <asias@redhat.com>
> > ---
> >  virt/kvm/kvm_main.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 8fd325a..3c8a992 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -3078,13 +3078,14 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
> >  	int r;
> >  	int cpu;
> > 
> > -	r = kvm_irqfd_init();
> > -	if (r)
> > -		goto out_irqfd;
> >  	r = kvm_arch_init(opaque);
> >  	if (r)
> >  		goto out_fail;
> > 
> > +	r = kvm_irqfd_init();
> > +	if (r)
> > +		goto out_irqfd;
> > +
> >  	if (!zalloc_cpumask_var(&cpus_hardware_enabled, GFP_KERNEL)) {
> >  		r = -ENOMEM;
> >  		goto out_free_0;
> > @@ -3159,10 +3160,10 @@ out_free_1:
> >  out_free_0a:
> >  	free_cpumask_var(cpus_hardware_enabled);
> >  out_free_0:
> > -	kvm_arch_exit();
> > -out_fail:
> >  	kvm_irqfd_exit();
> >  out_irqfd:
> > +	kvm_arch_exit();
> > +out_fail:
> >  	return r;
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_init);