Re: [PATCH v7 13/14] KVM: Enable and expose KVM_MEM_PRIVATE

Gupta, Pankaj
2022-07-19T09:55:33Z

> Register private memslot to fd-based memory backing store and handle the
> memfile notifiers to zap the existing mappings.
>
> Currently the register is happened at memslot creating time and the
> initial support does not include page migration/swap.
>
> KVM_MEM_PRIVATE is not exposed by default, architecture code can turn
> on it by implementing kvm_arch_private_mem_supported().
>
> A 'kvm' reference is added in memslot structure since in
> memfile_notifier callbacks we can only obtain a memslot reference while
> kvm is need to do the zapping.
>
> Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> 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 | 117 ++++++++++++++++++++++++++++++++++++---
> 2 files changed, 109 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 8f56426aa1e3..4e5a0db68799 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -584,6 +584,7 @@ struct kvm_memory_slot {
> struct file *private_file;
> loff_t private_offset;
> struct memfile_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 bb714c2a4b06..d6f7e074cab2 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -941,6 +941,63 @@ static int kvm_vm_ioctl_set_encrypted_region(struct kvm *kvm, unsigned int ioctl
>
> return r;
> }
> +
> +static void kvm_memfile_notifier_invalidate(struct memfile_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 memfile_notifier_ops kvm_memfile_notifier_ops = {
> + .invalidate = kvm_memfile_notifier_invalidate,
> +};
> +
> +#define KVM_MEMFILE_FLAGS (MEMFILE_F_USER_INACCESSIBLE | \
> + MEMFILE_F_UNMOVABLE | \
> + MEMFILE_F_UNRECLAIMABLE)
> +
> +static inline int kvm_private_mem_register(struct kvm_memory_slot *slot)
> +{
> + slot->notifier.ops = &kvm_memfile_notifier_ops;
> + return memfile_register_notifier(slot->private_file, KVM_MEMFILE_FLAGS,
> + &slot->notifier);
> +}
> +
> +static inline void kvm_private_mem_unregister(struct kvm_memory_slot *slot)
> +{
> + memfile_unregister_notifier(&slot->notifier);
> +}
> +
> +#else /* !CONFIG_HAVE_KVM_PRIVATE_MEM */
> +
> +static inline int kvm_private_mem_register(struct kvm_memory_slot *slot)
> +{
> + WARN_ON_ONCE(1);
> + return -EOPNOTSUPP;
> +}
> +
> +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
> @@ -987,6 +1044,11 @@ 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);
> @@ -1548,10 +1610,16 @@ bool __weak kvm_arch_private_mem_supported(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_private_mem_supported(kvm))
> + valid_flags |= KVM_MEM_PRIVATE;
> +#endif
> +
> #ifdef __KVM_HAVE_READONLY_MEM
> valid_flags |= KVM_MEM_READONLY;
> #endif
> @@ -1627,6 +1695,12 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
> {
> int r;
>
> + if (change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE) {
> + r = kvm_private_mem_register(new);
> + if (r)
> + return r;
> + }
> +
> /*
> * If dirty logging is disabled, nullify the bitmap; the old bitmap
> * will be freed on "commit". If logging is enabled in both old and
> @@ -1655,6 +1729,9 @@ 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;
> }
>
> @@ -1952,7 +2029,7 @@ 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;
>
> @@ -1971,6 +2048,10 @@ 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)
> @@ -2009,6 +2090,9 @@ 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))
> @@ -2037,10 +2121,27 @@ 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;
> + 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);
> @@ -4712,12 +4813,10 @@ static long kvm_vm_ioctl(struct file *filp,
> (u32 __user *)(argp + offsetof(typeof(mem), flags))))
> goto out;
>
> - if (flags & KVM_MEM_PRIVATE) {
> - r = -EINVAL;
> - goto out;
> - }
> -
> - size = sizeof(struct kvm_userspace_memory_region);
> + if (flags & KVM_MEM_PRIVATE)
> + size = sizeof(struct kvm_userspace_memory_region_ext);

Not sure if we use kvm_userspace_memory_region_ext or
kvm_user_mem_region, just for readability.

> + else
> + size = sizeof(struct kvm_userspace_memory_region);
>
> if (copy_from_user(&mem, argp, size))
> goto out;