[PATCH v3 0/6] KVM: Clean up debugfs init/destroy

Oliver Upton
2022-07-20T09:23:30Z

The way that KVM handles debugfs init/destroy is somewhat sloppy. Even
though debugfs is stood up after kvm_create_vm(), it is torn down from
kvm_destroy_vm(). There exists a window where we need to tear down a VM
before debugfs is created, requiring delicate handling.

This series cleans up the debugfs lifecycle by fully tying it to the
VM's init/destroy pattern.

First two patches hoist some unrelated stats initialization to a more
appropriate place for kvm and kvm_vcpu.

The next 3 patches are the meat of the series, changing around the
initialization order to get an FD early and wiring in debugfs
initialization to kvm_create_vm().

Lastly, patch 6 is essentially a revert of Sean's fix [1] for a NULL deref
in debugfs, though I stopped short of an outright revert since that one
went to stable and is still entirely correct.

"Works on my machine", and with luck it will on yours too.

[1] 5c697c367a66 ("KVM: Initialize debugfs_dentry when a VM is created to avoid NULL deref")

v1: http://lore.kernel.org/r/20220415201542.1496582-1-oupton@google.com
v2: https://lore.kernel.org/kvm/20220518175811.2758661-1-oupton@google.com

v1 -> v2:
- Don't conflate debugfs+stats. Initialize stats_id outside of the
context of debugfs (Sean)
- Pass around the FD as a string to avoid subsequent KVM changes
inappropriately using the FD (Sean)

v2 -> v3:
- Spare readers from needing to refer to the title of a commit (Sean)
- Crack fd stringization and move of kvm_create_vm_debugfs() into two
patches (Sean)
- Fix a bug that crops up in the middle of the series. Failed to pass
the fd through to kvm_create_vm_debugfs()

Oliver Upton (6):
KVM: Shove vm stats_id init into kvm_create_vm()
KVM: Shove vcpu stats_id init into kvm_vcpu_init()
KVM: Get an fd before creating the VM
KVM: Pass the name of the VM fd to kvm_create_vm_debugfs()
KVM: Actually create debugfs in kvm_create_vm()
KVM: Hoist debugfs_dentry init to kvm_create_vm_debugfs() (again)

virt/kvm/kvm_main.c | 91 +++++++++++++++++++++++++--------------------
1 file changed, 50 insertions(+), 41 deletions(-)

base-commit: 8031d87aa9953ddeb047a5356ebd0b240c30f233
--
2.37.0.170.g444d1eabd0-goog