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charset="UTF-8" X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 68DF8C0002 X-Stat-Signature: xpzzzqz7j6dwwnj1795q6bawxkxiraqt X-Rspam-User: X-HE-Tag: 1785240707-411930 X-HE-Meta: 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 FoYb9TNR 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: - Add a weak reference 'vm_file' in struct kvm under CONFIG_LIVEUPDATE_GUEST_MEMFD to enable reverse file resolution without circular lifetime dependencies. Signed-off-by: Tarun Sahu --- include/linux/kvm_host.h | 12 ++++++++++++ virt/kvm/kvm_main.c | 26 ++++++++++++++++++++++++++ 2 files changed, 38 insertions(+) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index d9908c19e42f..8da9589425ee 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -874,6 +874,18 @@ struct kvm { #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES /* Protected by slots_lock (for writes) and RCU (for reads) */ struct xarray mem_attr_array; +#endif +#ifdef CONFIG_LIVEUPDATE_GUEST_MEMFD + /* + * Weak reference to the VFS file backing this KVM instance. Stored + * without incrementing the file refcount to prevent a circular lifetime + * dependency (since file->private_data already pins this struct kvm). + * Used exclusively to resolve the file pointer back from struct kvm. + * + * Written/cleared via rcu_assign_pointer() and read locklessly under + * RCU (e.g. via get_file_active() to prevent ABA races). + */ + struct file __rcu *vm_file; #endif char stats_id[KVM_STATS_NAME_SIZE]; }; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 701d4596a91c..14c32541ae34 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1346,6 +1346,19 @@ static int kvm_vm_release(struct inode *inode, struct file *filp) { struct kvm *kvm = filp->private_data; +#ifdef CONFIG_LIVEUPDATE_GUEST_MEMFD + /* + * Clear the weak reference of the vm file. + * In case vm file is closed by userspace, but kvm still has + * other users like vCPUs, clearing this pointer ensures + * that we don't have a dangling pointer to a closed file. + * + * Cleared via rcu_assign_pointer() to ensure proper memory visibility + * for concurrent lockless readers under RCU. + */ + rcu_assign_pointer(kvm->vm_file, NULL); +#endif + kvm_irqfd_release(kvm); kvm_put_kvm(kvm); @@ -5488,6 +5501,19 @@ struct file *kvm_create_vm_file(unsigned long type, const char *fdname) return file; } +#ifdef CONFIG_LIVEUPDATE_GUEST_MEMFD + /* + * Weak reference to the file (without get_file()) to prevent a circular + * dependency. Safe because the file's release path clears this pointer + * and drops its reference to the VM. + * + * Written via rcu_assign_pointer() because the pointer can be read + * locklessly under RCU (e.g., in kvm_gmem_luo_preserve() via + * get_file_active() to prevent lockless ABA races). + */ + rcu_assign_pointer(kvm->vm_file, file); +#endif + /* * Don't call kvm_put_kvm anymore at this point; file->f_op is * already set, with ->release() being kvm_vm_release(). In error -- 2.55.0.229.g6434b31f56-goog