On Tue, Aug 16, 2022 at 05:39:35AM +0000, Sean Christopherson wrote: > Properly unwind VM creation if kvm_create_vm_debugfs() fails. A recent > change to invoke kvm_create_vm_debug() in kvm_create_vm() was led astray typo: kvm_create_vm_debugfs() > by buggy try_get_module() handling adding by commit 5f6de5cbebee ("KVM: > Prevent module exit until all VMs are freed"). The debugfs error path > effectively inherits the bad error path of try_module_get(), e.g. KVM > leaves the to-be-free VM on vm_list even though KVM appears to do the > right thing by calling module_put() and falling through. > > Opportunistically hoist kvm_create_vm_debugfs() above the call to > kvm_arch_post_init_vm() so that the "post-init" arch hook is actually > invoked after the VM is initialized (ignoring kvm_coalesced_mmio_init() > for the moment). x86 is the only non-nop implementation of the post-init > hook, and it doesn't allocate/initialize any objects that are reachable > via debugfs code (spawns a kthread worker for the NX huge page mitigation). > > Leave the buggy try_get_module() alone for now, it will be fixed in a > separate commit. > > Fixes: b74ed7a68ec1 ("KVM: Actually create debugfs in kvm_create_vm()") > Reported-by: syzbot+744e173caec2e1627ee0@xxxxxxxxxxxxxxxxxxxxxxxxx > Cc: Oliver Upton <oliver.upton@xxxxxxxxx> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Fun times! Thanks for the fix Sean. Reviewed-by: Oliver Upton <oliver.upton@xxxxxxxxx> -- Best, Oliver