Introduce core infrastructure to support VM preservation with LUO. First two changes are just refactoring, no functional change, third change introduces a new member in struct kvm. - Move ITOA_MAX_LEN to kvm_mm.h for reuse by upcoming kvm_luo code. - Add a public kvm_create_vm_file() helper wrapping kvm_create_vm() and anon_inode_getfile() to provide a unified VM file creation API. - Track a weak reference to the backing file in struct kvm under CONFIG_LIVEUPDATE_GUEST_MEMFD to enable reverse file resolution without circular lifetime dependencies.
Signed-off-by: Tarun Sahu <[email protected]> --- include/linux/kvm_host.h | 14 +++++++ virt/kvm/kvm_main.c | 79 +++++++++++++++++++++++++++++----------- virt/kvm/kvm_mm.h | 3 ++ 3 files changed, 75 insertions(+), 21 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 4c14aee1fb06..9111a28637af 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 *vm_file; #endif char stats_id[KVM_STATS_NAME_SIZE]; }; @@ -1074,7 +1086,9 @@ void kvm_get_kvm(struct kvm *kvm); bool kvm_get_kvm_safe(struct kvm *kvm); void kvm_put_kvm(struct kvm *kvm); bool file_is_kvm(struct file *file); +struct file *kvm_create_vm_file(unsigned long type, const char *fdname); void kvm_put_kvm_no_destroy(struct kvm *kvm); +void kvm_uevent_notify_vm_create(struct kvm *kvm); static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id) { diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 89489996fbc1..65f0c5fb353e 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -67,9 +67,6 @@ #include <linux/kvm_dirty_ring.h> -/* Worst case buffer size needed for holding an integer. */ -#define ITOA_MAX_LEN 12 - MODULE_AUTHOR("Qumranet"); MODULE_DESCRIPTION("Kernel-based Virtual Machine (KVM) Hypervisor"); MODULE_LICENSE("GPL"); @@ -1349,6 +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); @@ -5476,11 +5486,47 @@ bool file_is_kvm(struct file *file) } EXPORT_SYMBOL_FOR_KVM_INTERNAL(file_is_kvm); +struct file *kvm_create_vm_file(unsigned long type, const char *fdname) +{ + struct kvm *kvm = kvm_create_vm(type, fdname); + struct file *file; + + if (IS_ERR(kvm)) + return ERR_CAST(kvm); + + file = anon_inode_getfile("kvm-vm", &kvm_vm_fops, kvm, O_RDWR); + if (IS_ERR(file)) { + kvm_put_kvm(kvm); + 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 + * cases it will be called by the final fput(file) and will take + * care of doing kvm_put_kvm(kvm). + */ + + return file; +} + static int kvm_dev_ioctl_create_vm(unsigned long type) { char fdname[ITOA_MAX_LEN + 1]; int r, fd; - struct kvm *kvm; struct file *file; fd = get_unused_fd_flags(O_CLOEXEC); @@ -5489,31 +5535,17 @@ static int kvm_dev_ioctl_create_vm(unsigned long type) snprintf(fdname, sizeof(fdname), "%d", fd); - kvm = kvm_create_vm(type, fdname); - if (IS_ERR(kvm)) { - r = PTR_ERR(kvm); - goto put_fd; - } - - file = anon_inode_getfile("kvm-vm", &kvm_vm_fops, kvm, O_RDWR); + file = kvm_create_vm_file(type, fdname); if (IS_ERR(file)) { r = PTR_ERR(file); - goto put_kvm; + goto put_fd; } - /* - * Don't call kvm_put_kvm anymore at this point; file->f_op is - * already set, with ->release() being kvm_vm_release(). In error - * cases it will be called by the final fput(file) and will take - * care of doing kvm_put_kvm(kvm). - */ - kvm_uevent_notify_change(KVM_EVENT_CREATE_VM, kvm); + kvm_uevent_notify_change(KVM_EVENT_CREATE_VM, file->private_data); fd_install(fd, file); return fd; -put_kvm: - kvm_put_kvm(kvm); put_fd: put_unused_fd(fd); return r; @@ -6341,6 +6373,11 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm) kfree(env); } +void kvm_uevent_notify_vm_create(struct kvm *kvm) +{ + kvm_uevent_notify_change(KVM_EVENT_CREATE_VM, kvm); +} + static void kvm_init_debug(void) { const struct file_operations *fops; diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h index 9fcc5d5b7f8d..7aa1d65c3d46 100644 --- a/virt/kvm/kvm_mm.h +++ b/virt/kvm/kvm_mm.h @@ -3,6 +3,9 @@ #ifndef __KVM_MM_H__ #define __KVM_MM_H__ 1 +/* Worst case buffer size needed for holding an integer as a string. */ +#define ITOA_MAX_LEN 12 + /* * Architectures can choose whether to use an rwlock or spinlock * for the mmu_lock. These macros, for use in common code -- 2.54.0.563.g4f69b47b94-goog
