| Message ID | 20220310140911.50924-11-chao.p.peng@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: mm: fd-based approach for supporting KVM guest private memory | expand |
On Thu, Mar 10, 2022, Chao Peng wrote: > Add 'notifier' to memslot to make it a memfile_notifier node and then > register it to memory backing store via memfile_register_notifier() when > memslot gets created. When memslot is deleted, do the reverse with > memfile_unregister_notifier(). Note each KVM memslot can be registered > to different memory backing stores (or the same backing store but at > different offset) independently. > > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com> > --- > include/linux/kvm_host.h | 1 + > virt/kvm/kvm_main.c | 75 ++++++++++++++++++++++++++++++++++++---- > 2 files changed, 70 insertions(+), 6 deletions(-) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 6e1d770d6bf8..9b175aeca63f 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -567,6 +567,7 @@ struct kvm_memory_slot { > struct file *private_file; > loff_t private_offset; > struct memfile_pfn_ops *pfn_ops; > + struct memfile_notifier notifier; > }; > > static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot) > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index d11a2628b548..67349421eae3 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -840,6 +840,37 @@ static int kvm_init_mmu_notifier(struct kvm *kvm) > > #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */ > > +#ifdef CONFIG_MEMFILE_NOTIFIER > +static inline int kvm_memfile_register(struct kvm_memory_slot *slot) This is a good oppurtunity to hide away the memfile details a bit. Maybe kvm_private_mem_{,un}register()? > +{ > + return memfile_register_notifier(file_inode(slot->private_file), > + &slot->notifier, > + &slot->pfn_ops); > +} > + > +static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot) > +{ > + if (slot->private_file) { > + memfile_unregister_notifier(file_inode(slot->private_file), > + &slot->notifier); > + fput(slot->private_file); This should not do fput(), it makes the helper imbalanced with respect to the register path and will likely lead to double fput(). Indeed, if preparing the region fails, __kvm_set_memory_region() will double up on fput() due to checking its local "file" for null, not slot->private for null. > + slot->private_file = NULL; > + } > +} > + > +#else /* !CONFIG_MEMFILE_NOTIFIER */ > + > +static inline int kvm_memfile_register(struct kvm_memory_slot *slot) > +{ This should WARN_ON_ONCE(). Ditto for unregister. > + return -EOPNOTSUPP; > +} > + > +static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot) > +{ > +} > + > +#endif /* CONFIG_MEMFILE_NOTIFIER */ > + > #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER > static int kvm_pm_notifier_call(struct notifier_block *bl, > unsigned long state, > @@ -884,6 +915,9 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot) > /* This does not remove the slot from struct kvm_memslots data structures */ > static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot) > { > + if (slot->flags & KVM_MEM_PRIVATE) > + kvm_memfile_unregister(slot); With fput() move out of unregister, this needs to be: if (slot->flags & KVM_MEM_PRIVATE) { kvm_private_mem_unregister(slot); fput(slot->private_file); } > + > kvm_destroy_dirty_bitmap(slot); > > kvm_arch_free_memslot(kvm, slot); > @@ -1738,6 +1772,12 @@ static int kvm_set_memslot(struct kvm *kvm, > kvm_invalidate_memslot(kvm, old, invalid_slot); > } > > + if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) { > + r = kvm_memfile_register(new); > + if (r) > + return r; > + } This belongs in kvm_prepare_memory_region(). The shenanigans for DELETE and MOVE are special. > + > r = kvm_prepare_memory_region(kvm, old, new, change); > if (r) { > /* > @@ -1752,6 +1792,10 @@ static int kvm_set_memslot(struct kvm *kvm, > } else { > mutex_unlock(&kvm->slots_arch_lock); > } > + > + if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) > + kvm_memfile_unregister(new); > + > return r; > } > > @@ -1817,6 +1861,7 @@ int __kvm_set_memory_region(struct kvm *kvm, > enum kvm_mr_change change; > unsigned long npages; > gfn_t base_gfn; > + struct file *file = NULL; Nit, naming this private_file would help understand its use. Though I think it's easier to not have a local variable. More below. > int as_id, id; > int r; > > @@ -1890,14 +1935,24 @@ int __kvm_set_memory_region(struct kvm *kvm, > return 0; > } > > + if (mem->flags & KVM_MEM_PRIVATE) { > + file = fdget(region_ext->private_fd).file; This can use fget() instead of fdget(). > + if (!file) > + return -EINVAL; > + } > + > if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) && > - kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) > - return -EEXIST; > + kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) { > + r = -EEXIST; > + goto out; > + } > > /* Allocate a slot that will persist in the memslot. */ > new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT); > - if (!new) > - return -ENOMEM; > + if (!new) { > + r = -ENOMEM; > + goto out; > + } > > new->as_id = as_id; > new->id = id; > @@ -1905,10 +1960,18 @@ int __kvm_set_memory_region(struct kvm *kvm, > new->npages = npages; > new->flags = mem->flags; > new->userspace_addr = mem->userspace_addr; > + new->private_file = file; > + new->private_offset = mem->flags & KVM_MEM_PRIVATE ? > + region_ext->private_offset : 0; "new" is zero-allocated, so all the private stuff, including the fget(), can be wrapped in a single KVM_MEM_PRIVATE check. Moving fget() eliminates the number of gotos needed (the above -EEXIST and -ENOMEM paths don't need to be modified). > r = kvm_set_memslot(kvm, old, new, change); > - if (r) > - kfree(new); > + if (!r) > + return r; Use goto, e.g. if (r) goto out; return 0; Burying the happy path in a taken if-statement is confusing and error prone, mostly because it breaks well-established kernel patterns. Note, there's no need for a separate out_free since new->private_file will be NULL in either case. I don't have a strong preference, I just find it easier to read code that's more explicit, but I'm a-ok collapsing them into a single label. if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) && kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) return -EEXIST; /* Allocate a slot that will persist in the memslot. */ new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT); if (!new) return -ENOMEM; new->as_id = as_id; new->id = id; new->base_gfn = base_gfn; new->npages = npages; new->flags = mem->flags; new->userspace_addr = mem->userspace_addr; if (mem->flags & KVM_MEM_PRIVATE) { new->private_file = fget(mem->private_fd); if (!new->private_file) { r = -EINVAL; goto out_free; } new->private_offset = mem->private_offset; } r = kvm_set_memslot(kvm, old, new, change); if (r) goto out; return 0; out: if (new->private_file) fput(new->private_file); out_free: kfree(new); return r;
On Tue, Mar 29, 2022 at 07:01:52PM +0000, Sean Christopherson wrote: > On Thu, Mar 10, 2022, Chao Peng wrote: > > Add 'notifier' to memslot to make it a memfile_notifier node and then > > register it to memory backing store via memfile_register_notifier() when > > memslot gets created. When memslot is deleted, do the reverse with > > memfile_unregister_notifier(). Note each KVM memslot can be registered > > to different memory backing stores (or the same backing store but at > > different offset) independently. > > > > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com> > > --- > > include/linux/kvm_host.h | 1 + > > virt/kvm/kvm_main.c | 75 ++++++++++++++++++++++++++++++++++++---- > > 2 files changed, 70 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index 6e1d770d6bf8..9b175aeca63f 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -567,6 +567,7 @@ struct kvm_memory_slot { > > struct file *private_file; > > loff_t private_offset; > > struct memfile_pfn_ops *pfn_ops; > > + struct memfile_notifier notifier; > > }; > > > > static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index d11a2628b548..67349421eae3 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -840,6 +840,37 @@ static int kvm_init_mmu_notifier(struct kvm *kvm) > > > > #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */ > > > > +#ifdef CONFIG_MEMFILE_NOTIFIER > > +static inline int kvm_memfile_register(struct kvm_memory_slot *slot) > > This is a good oppurtunity to hide away the memfile details a bit. Maybe > kvm_private_mem_{,un}register()? Happy to change. > > > +{ > > + return memfile_register_notifier(file_inode(slot->private_file), > > + &slot->notifier, > > + &slot->pfn_ops); > > +} > > + > > +static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot) > > +{ > > + if (slot->private_file) { > > + memfile_unregister_notifier(file_inode(slot->private_file), > > + &slot->notifier); > > + fput(slot->private_file); > > This should not do fput(), it makes the helper imbalanced with respect to the > register path and will likely lead to double fput(). Indeed, if preparing the > region fails, __kvm_set_memory_region() will double up on fput() due to checking > its local "file" for null, not slot->private for null. Right. > > > + slot->private_file = NULL; > > + } > > +} > > + > > +#else /* !CONFIG_MEMFILE_NOTIFIER */ > > + > > +static inline int kvm_memfile_register(struct kvm_memory_slot *slot) > > +{ > > This should WARN_ON_ONCE(). Ditto for unregister. > > > + return -EOPNOTSUPP; > > +} > > + > > +static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot) > > +{ > > +} > > + > > +#endif /* CONFIG_MEMFILE_NOTIFIER */ > > + > > #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER > > static int kvm_pm_notifier_call(struct notifier_block *bl, > > unsigned long state, > > @@ -884,6 +915,9 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot) > > /* This does not remove the slot from struct kvm_memslots data structures */ > > static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot) > > { > > + if (slot->flags & KVM_MEM_PRIVATE) > > + kvm_memfile_unregister(slot); > > With fput() move out of unregister, this needs to be: Agreed. > > if (slot->flags & KVM_MEM_PRIVATE) { > kvm_private_mem_unregister(slot); > fput(slot->private_file); > } > > + > > kvm_destroy_dirty_bitmap(slot); > > > > kvm_arch_free_memslot(kvm, slot); > > @@ -1738,6 +1772,12 @@ static int kvm_set_memslot(struct kvm *kvm, > > kvm_invalidate_memslot(kvm, old, invalid_slot); > > } > > > > + if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) { > > + r = kvm_memfile_register(new); > > + if (r) > > + return r; > > + } > > This belongs in kvm_prepare_memory_region(). The shenanigans for DELETE and MOVE > are special. Sure. > > > + > > r = kvm_prepare_memory_region(kvm, old, new, change); > > if (r) { > > /* > > @@ -1752,6 +1792,10 @@ static int kvm_set_memslot(struct kvm *kvm, > > } else { > > mutex_unlock(&kvm->slots_arch_lock); > > } > > + > > + if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) > > + kvm_memfile_unregister(new); > > + > > return r; > > } > > > > @@ -1817,6 +1861,7 @@ int __kvm_set_memory_region(struct kvm *kvm, > > enum kvm_mr_change change; > > unsigned long npages; > > gfn_t base_gfn; > > + struct file *file = NULL; > > Nit, naming this private_file would help understand its use. Though I think it's > easier to not have a local variable. More below. > > > int as_id, id; > > int r; > > > > @@ -1890,14 +1935,24 @@ int __kvm_set_memory_region(struct kvm *kvm, > > return 0; > > } > > > > + if (mem->flags & KVM_MEM_PRIVATE) { > > + file = fdget(region_ext->private_fd).file; > > This can use fget() instead of fdget(). > > > + if (!file) > > + return -EINVAL; > > + } > > + > > if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) && > > - kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) > > - return -EEXIST; > > + kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) { > > + r = -EEXIST; > > + goto out; > > + } > > > > /* Allocate a slot that will persist in the memslot. */ > > new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT); > > - if (!new) > > - return -ENOMEM; > > + if (!new) { > > + r = -ENOMEM; > > + goto out; > > + } > > > > new->as_id = as_id; > > new->id = id; > > @@ -1905,10 +1960,18 @@ int __kvm_set_memory_region(struct kvm *kvm, > > new->npages = npages; > > new->flags = mem->flags; > > new->userspace_addr = mem->userspace_addr; > > + new->private_file = file; > > + new->private_offset = mem->flags & KVM_MEM_PRIVATE ? > > + region_ext->private_offset : 0; > > "new" is zero-allocated, so all the private stuff, including the fget(), can be > wrapped in a single KVM_MEM_PRIVATE check. Moving fget() eliminates the number > of gotos needed (the above -EEXIST and -ENOMEM paths don't need to be modified). > > > r = kvm_set_memslot(kvm, old, new, change); > > - if (r) > > - kfree(new); > > + if (!r) > > + return r; > > Use goto, e.g. > > if (r) > goto out; > > return 0; > > Burying the happy path in a taken if-statement is confusing and error prone, > mostly because it breaks well-established kernel patterns. Note, there's no need > for a separate out_free since new->private_file will be NULL in either case. I > don't have a strong preference, I just find it easier to read code that's more > explicit, but I'm a-ok collapsing them into a single label. Will follow this, thanks for the detailed suggestion. Chao > > if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) && > kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) > return -EEXIST; > > /* Allocate a slot that will persist in the memslot. */ > new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT); > if (!new) > return -ENOMEM; > > new->as_id = as_id; > new->id = id; > new->base_gfn = base_gfn; > new->npages = npages; > new->flags = mem->flags; > new->userspace_addr = mem->userspace_addr; > > if (mem->flags & KVM_MEM_PRIVATE) { > new->private_file = fget(mem->private_fd); > if (!new->private_file) { > r = -EINVAL; > goto out_free; > } > new->private_offset = mem->private_offset; > } > > r = kvm_set_memslot(kvm, old, new, change); > if (r) > goto out; > > return 0; > > out: > if (new->private_file) > fput(new->private_file); > > out_free: > kfree(new); > return r;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 6e1d770d6bf8..9b175aeca63f 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -567,6 +567,7 @@ struct kvm_memory_slot { struct file *private_file; loff_t private_offset; struct memfile_pfn_ops *pfn_ops; + struct memfile_notifier notifier; }; static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index d11a2628b548..67349421eae3 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -840,6 +840,37 @@ static int kvm_init_mmu_notifier(struct kvm *kvm) #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */ +#ifdef CONFIG_MEMFILE_NOTIFIER +static inline int kvm_memfile_register(struct kvm_memory_slot *slot) +{ + return memfile_register_notifier(file_inode(slot->private_file), + &slot->notifier, + &slot->pfn_ops); +} + +static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot) +{ + if (slot->private_file) { + memfile_unregister_notifier(file_inode(slot->private_file), + &slot->notifier); + fput(slot->private_file); + slot->private_file = NULL; + } +} + +#else /* !CONFIG_MEMFILE_NOTIFIER */ + +static inline int kvm_memfile_register(struct kvm_memory_slot *slot) +{ + return -EOPNOTSUPP; +} + +static inline void kvm_memfile_unregister(struct kvm_memory_slot *slot) +{ +} + +#endif /* CONFIG_MEMFILE_NOTIFIER */ + #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER static int kvm_pm_notifier_call(struct notifier_block *bl, unsigned long state, @@ -884,6 +915,9 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot) /* This does not remove the slot from struct kvm_memslots data structures */ static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot) { + if (slot->flags & KVM_MEM_PRIVATE) + kvm_memfile_unregister(slot); + kvm_destroy_dirty_bitmap(slot); kvm_arch_free_memslot(kvm, slot); @@ -1738,6 +1772,12 @@ static int kvm_set_memslot(struct kvm *kvm, kvm_invalidate_memslot(kvm, old, invalid_slot); } + if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) { + r = kvm_memfile_register(new); + if (r) + return r; + } + r = kvm_prepare_memory_region(kvm, old, new, change); if (r) { /* @@ -1752,6 +1792,10 @@ static int kvm_set_memslot(struct kvm *kvm, } else { mutex_unlock(&kvm->slots_arch_lock); } + + if (new->flags & KVM_MEM_PRIVATE && change == KVM_MR_CREATE) + kvm_memfile_unregister(new); + return r; } @@ -1817,6 +1861,7 @@ int __kvm_set_memory_region(struct kvm *kvm, enum kvm_mr_change change; unsigned long npages; gfn_t base_gfn; + struct file *file = NULL; int as_id, id; int r; @@ -1890,14 +1935,24 @@ int __kvm_set_memory_region(struct kvm *kvm, return 0; } + if (mem->flags & KVM_MEM_PRIVATE) { + file = fdget(region_ext->private_fd).file; + if (!file) + return -EINVAL; + } + if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) && - kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) - return -EEXIST; + kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) { + r = -EEXIST; + goto out; + } /* Allocate a slot that will persist in the memslot. */ new = kzalloc(sizeof(*new), GFP_KERNEL_ACCOUNT); - if (!new) - return -ENOMEM; + if (!new) { + r = -ENOMEM; + goto out; + } new->as_id = as_id; new->id = id; @@ -1905,10 +1960,18 @@ int __kvm_set_memory_region(struct kvm *kvm, new->npages = npages; new->flags = mem->flags; new->userspace_addr = mem->userspace_addr; + new->private_file = file; + new->private_offset = mem->flags & KVM_MEM_PRIVATE ? + region_ext->private_offset : 0; r = kvm_set_memslot(kvm, old, new, change); - if (r) - kfree(new); + if (!r) + return r; + + kfree(new); +out: + if (file) + fput(file); return r; } EXPORT_SYMBOL_GPL(__kvm_set_memory_region);