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authorSean Christopherson <seanjc@google.com>2022-08-16 05:39:35 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2022-08-19 04:02:30 -0400
commit4ba4f41942745f1906c06868a4acc6c926463f53 (patch)
tree66bcb913881851097e88ab25b5b4a9f08190161a /virt
parent568035b01cfb107af8d2e4bd2fb9aea22cf5b868 (diff)
downloadlwn-4ba4f41942745f1906c06868a4acc6c926463f53.tar.gz
lwn-4ba4f41942745f1906c06868a4acc6c926463f53.zip
KVM: Properly unwind VM creation if creating debugfs fails
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 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@syzkaller.appspotmail.com Cc: Oliver Upton <oliver.upton@linux.dev> Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Oliver Upton <oliver.upton@linux.dev> Message-Id: <20220816053937.2477106-2-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/kvm_main.c16
1 files changed, 8 insertions, 8 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 515dfe9d3bcf..ee5f48cc100b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1211,9 +1211,13 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
if (r)
goto out_err_no_mmu_notifier;
+ r = kvm_create_vm_debugfs(kvm, fdname);
+ if (r)
+ goto out_err_no_debugfs;
+
r = kvm_arch_post_init_vm(kvm);
if (r)
- goto out_err_mmu_notifier;
+ goto out_err;
mutex_lock(&kvm_lock);
list_add(&kvm->vm_list, &vm_list);
@@ -1229,18 +1233,14 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
*/
if (!try_module_get(kvm_chardev_ops.owner)) {
r = -ENODEV;
- goto out_err_mmu_notifier;
- }
-
- r = kvm_create_vm_debugfs(kvm, fdname);
- if (r)
goto out_err;
+ }
return kvm;
out_err:
- module_put(kvm_chardev_ops.owner);
-out_err_mmu_notifier:
+ kvm_destroy_vm_debugfs(kvm);
+out_err_no_debugfs:
#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
if (kvm->mmu_notifier.ops)
mmu_notifier_unregister(&kvm->mmu_notifier, current->mm);