On Thu, Oct 06, 2022 at 09:55:31AM +0100, Fuad Tabba wrote:
> Hi,
>
> On Thu, Sep 15, 2022 at 3:37 PM Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
> >
> > Expose KVM_MEM_PRIVATE and memslot fields private_fd/offset to
> > userspace. KVM will register/unregister private memslot to fd-based
> > memory backing store and response to invalidation event from
> > inaccessible_notifier to zap the existing memory mappings in the
> > secondary page table.
> >
> > Whether KVM_MEM_PRIVATE is actually exposed to userspace is determined
> > by architecture code which can turn on it by overriding the default
> > kvm_arch_has_private_mem().
> >
> > A 'kvm' reference is added in memslot structure since in
> > inaccessible_notifier callback we can only obtain a memslot reference
> > but 'kvm' is needed to do the zapping.
> >
> > Co-developed-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > ---
> > include/linux/kvm_host.h | 1 +
> > virt/kvm/kvm_main.c | 116 +++++++++++++++++++++++++++++++++++++--
> > 2 files changed, 111 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index b9906cdf468b..cb4eefac709c 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -589,6 +589,7 @@ struct kvm_memory_slot {
> > struct file *private_file;
> > loff_t private_offset;
> > struct inaccessible_notifier notifier;
> > + struct kvm *kvm;
> > };
> >
> > static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 97d893f7482c..87e239d35b96 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -983,6 +983,57 @@ static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> > xa_erase(&kvm->mem_attr_array, index);
> > return r;
> > }
> > +
> > +static void kvm_private_notifier_invalidate(struct inaccessible_notifier *notifier,
> > + pgoff_t start, pgoff_t end)
> > +{
> > + struct kvm_memory_slot *slot = container_of(notifier,
> > + struct kvm_memory_slot,
> > + notifier);
> > + unsigned long base_pgoff = slot->private_offset >> PAGE_SHIFT;
> > + gfn_t start_gfn = slot->base_gfn;
> > + gfn_t end_gfn = slot->base_gfn + slot->npages;
> > +
> > +
> > + if (start > base_pgoff)
> > + start_gfn = slot->base_gfn + start - base_pgoff;
> > +
> > + if (end < base_pgoff + slot->npages)
> > + end_gfn = slot->base_gfn + end - base_pgoff;
> > +
> > + if (start_gfn >= end_gfn)
> > + return;
> > +
> > + kvm_zap_gfn_range(slot->kvm, start_gfn, end_gfn);
> > +}
> > +
> > +static struct inaccessible_notifier_ops kvm_private_notifier_ops = {
> > + .invalidate = kvm_private_notifier_invalidate,
> > +};
> > +
> > +static inline void kvm_private_mem_register(struct kvm_memory_slot *slot)
> > +{
> > + slot->notifier.ops = &kvm_private_notifier_ops;
> > + inaccessible_register_notifier(slot->private_file, &slot->notifier);
> > +}
> > +
> > +static inline void kvm_private_mem_unregister(struct kvm_memory_slot *slot)
> > +{
> > + inaccessible_unregister_notifier(slot->private_file, &slot->notifier);
> > +}
> > +
> > +#else /* !CONFIG_HAVE_KVM_PRIVATE_MEM */
> > +
> > +static inline void kvm_private_mem_register(struct kvm_memory_slot *slot)
> > +{
> > + WARN_ON_ONCE(1);
> > +}
> > +
> > +static inline void kvm_private_mem_unregister(struct kvm_memory_slot *slot)
> > +{
> > + WARN_ON_ONCE(1);
> > +}
> > +
> > #endif /* CONFIG_HAVE_KVM_PRIVATE_MEM */
> >
> > #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
> > @@ -1029,6 +1080,11 @@ 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_private_mem_unregister(slot);
> > + fput(slot->private_file);
> > + }
> > +
> > kvm_destroy_dirty_bitmap(slot);
> >
> > kvm_arch_free_memslot(kvm, slot);
> > @@ -1600,10 +1656,16 @@ bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> > return false;
> > }
> >
> > -static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
> > +static int check_memory_region_flags(struct kvm *kvm,
> > + const struct kvm_user_mem_region *mem)
> > {
> > u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> >
> > +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> > + if (kvm_arch_has_private_mem(kvm))
> > + valid_flags |= KVM_MEM_PRIVATE;
> > +#endif
> > +
> > #ifdef __KVM_HAVE_READONLY_MEM
> > valid_flags |= KVM_MEM_READONLY;
> > #endif
> > @@ -1679,6 +1741,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
> > {
> > int r;
> >
> > + if (change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
> > + kvm_private_mem_register(new);
> > +
>
> >From the discussion I had with Kirill in the first patch *, should
> this check that the private_fd is inaccessible?
Yes I can add a check in KVM code, see below for where I want to add it.
>
> [*] https://lore.kernel.org/all/20221003110129.bbee7kawhw5ed745@xxxxxxxxxxxxxxxxx/
>
> Cheers,
> /fuad
>
> > /*
> > * If dirty logging is disabled, nullify the bitmap; the old bitmap
> > * will be freed on "commit". If logging is enabled in both old and
> > @@ -1707,6 +1772,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
> > if (r && new && new->dirty_bitmap && (!old || !old->dirty_bitmap))
> > kvm_destroy_dirty_bitmap(new);
> >
> > + if (r && change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
> > + kvm_private_mem_unregister(new);
> > +
> > return r;
> > }
> >
> > @@ -2004,7 +2072,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > int as_id, id;
> > int r;
> >
> > - r = check_memory_region_flags(mem);
> > + r = check_memory_region_flags(kvm, mem);
> > if (r)
> > return r;
> >
> > @@ -2023,6 +2091,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > !access_ok((void __user *)(unsigned long)mem->userspace_addr,
> > mem->memory_size))
> > return -EINVAL;
> > + if (mem->flags & KVM_MEM_PRIVATE &&
> > + (mem->private_offset & (PAGE_SIZE - 1) ||
> > + mem->private_offset > U64_MAX - mem->memory_size))
> > + return -EINVAL;
> > if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> > return -EINVAL;
> > if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> > @@ -2061,6 +2133,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
> > return -EINVAL;
> > } else { /* Modify an existing slot. */
> > + /* Private memslots are immutable, they can only be deleted. */
> > + if (mem->flags & KVM_MEM_PRIVATE)
> > + return -EINVAL;
> > if ((mem->userspace_addr != old->userspace_addr) ||
> > (npages != old->npages) ||
> > ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> > @@ -2089,10 +2164,27 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > 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;
The check will go here.
> > + goto out;
> > + }
> > + new->private_offset = mem->private_offset;
> > + }
> > +
> > + new->kvm = kvm;
> >
> > r = kvm_set_memslot(kvm, old, new, change);
> > if (r)
> > - kfree(new);
> > + goto out;
> > +
> > + return 0;
> > +
> > +out:
> > + if (new->private_file)
> > + fput(new->private_file);
> > + kfree(new);
> > return r;
> > }
> > EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> > @@ -4747,16 +4839,28 @@ static long kvm_vm_ioctl(struct file *filp,
> > }
> > case KVM_SET_USER_MEMORY_REGION: {
> > struct kvm_user_mem_region mem;
> > - unsigned long size = sizeof(struct kvm_userspace_memory_region);
> > + unsigned int flags_offset = offsetof(typeof(mem), flags);
> > + unsigned long size;
> > + u32 flags;
> >
> > kvm_sanity_check_user_mem_region_alias();
> >
> > + memset(&mem, 0, sizeof(mem));
> > +
> > r = -EFAULT;
> > - if (copy_from_user(&mem, argp, size);
> > + if (get_user(flags, (u32 __user *)(argp + flags_offset)))
> > + goto out;
> > +
> > + if (flags & KVM_MEM_PRIVATE)
> > + size = sizeof(struct kvm_userspace_memory_region_ext);
> > + else
> > + size = sizeof(struct kvm_userspace_memory_region);
> > +
> > + if (copy_from_user(&mem, argp, size))
> > goto out;
> >
> > r = -EINVAL;
> > - if (mem.flags & KVM_MEM_PRIVATE)
> > + if ((flags ^ mem.flags) & KVM_MEM_PRIVATE)
> > goto out;
> >
> > r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
> > --
> > 2.25.1
> >
