Hi Oliver,
On Mon, 04 Apr 2022 19:21:17 +0100,
Oliver Upton <oup...@google.com> wrote:
>
> Unfortunately, there is no guarantee that KVM was able to instantiate a
> debugfs directory for a particular VM. To that end, KVM shouldn't even
> attempt to create new debugfs files in this case. If the specified
> parent dentry is NULL, debugfs_create_file() will instantiate files at
> the root of debugfs.
>
> For arm64, it is possible to create the vgic-state file outside of a
> VM directory, the file is not cleaned up when a VM is destroyed.
> Nonetheless, the corresponding struct kvm is freed when the VM is
> destroyed.
>
> Nip the problem in the bud for all possible errant debugfs file
> creations by initializing kvm->debugfs_dentry to -ENOENT. In so doing,
> debugfs_create_file() will fail instead of creating the file in the root
> directory.
>
> Cc: sta...@kernel.org
> Fixes: 929f45e32499 ("kvm: no need to check return value of debugfs_create
> functions")
> Signed-off-by: Oliver Upton <oup...@google.com>
> ---
> virt/kvm/kvm_main.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 70e05af5ebea..04a426e65cb8 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -932,7 +932,7 @@ static void kvm_destroy_vm_debugfs(struct kvm *kvm)
> int kvm_debugfs_num_entries = kvm_vm_stats_header.num_desc +
> kvm_vcpu_stats_header.num_desc;
>
> - if (!kvm->debugfs_dentry)
> + if (!IS_ERR(kvm->debugfs_dentry))
> return;
Shouldn't this condition be inverted? It certainly looks odd.
>
> debugfs_remove_recursive(kvm->debugfs_dentry);
> @@ -955,6 +955,12 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
> int kvm_debugfs_num_entries = kvm_vm_stats_header.num_desc +
> kvm_vcpu_stats_header.num_desc;
>
> + /*
> + * Force subsequent debugfs file creations to fail if the VM directory
> + * is not created.
> + */
> + kvm->debugfs_dentry = ERR_PTR(-ENOENT);
> +
> if (!debugfs_initialized())
> return 0;
>
> @@ -5479,7 +5485,7 @@ static void kvm_uevent_notify_change(unsigned int type,
> struct kvm *kvm)
> }
> add_uevent_var(env, "PID=%d", kvm->userspace_pid);
>
> - if (kvm->debugfs_dentry) {
> + if (!IS_ERR(kvm->debugfs_dentry)) {
> char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL_ACCOUNT);
>
> if (p) {
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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