Re: [PATCH v9 8/8] KVM: Enable and expose KVM_MEM_PRIVATE

Fuad Tabba
2022-10-27T10:33:36Z

Hi,

On Tue, Oct 25, 2022 at 4:20 PM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> Expose KVM_MEM_PRIVATE and memslot fields restricted_fd/offset to
> userspace. KVM register/unregister private memslot to fd-based
> memory backing store and responses to invalidation event from
> restrictedmem_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
> restrictedmem_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@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 | 3 +-
> virt/kvm/kvm_main.c | 174 +++++++++++++++++++++++++++++++++++++--
> 2 files changed, 171 insertions(+), 6 deletions(-)

Reviewed-by: Fuad Tabba <tabba@google.com>

Thanks,
/fuad

>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 69300fc6d572..e27d62c30484 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -246,7 +246,7 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> #endif
>
>
> -#if defined(KVM_ARCH_WANT_MMU_NOTIFIER) || defined(CONFIG_KVM_GENERIC_PRIVATE_MEM)
> +#if defined(KVM_ARCH_WANT_MMU_NOTIFIER) || defined(CONFIG_HAVE_KVM_RESTRICTED_MEM)
> struct kvm_gfn_range {
> struct kvm_memory_slot *slot;
> gfn_t start;
> @@ -583,6 +583,7 @@ struct kvm_memory_slot {
> struct file *restricted_file;
> loff_t restricted_offset;
> struct restrictedmem_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 13a37b4d9e97..dae6a2c196ad 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1028,6 +1028,111 @@ static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> }
> #endif /* CONFIG_KVM_GENERIC_PRIVATE_MEM */
>
> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
> + pgoff_t start, pgoff_t end,
> + gfn_t *gfn_start, gfn_t *gfn_end)
> +{
> + unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
> +
> + if (start > base_pgoff)
> + *gfn_start = slot->base_gfn + start - base_pgoff;
> + else
> + *gfn_start = slot->base_gfn;
> +
> + if (end < base_pgoff + slot->npages)
> + *gfn_end = slot->base_gfn + end - base_pgoff;
> + else
> + *gfn_end = slot->base_gfn + slot->npages;
> +
> + if (*gfn_start >= *gfn_end)
> + return false;
> +
> + return true;
> +}
> +
> +static void kvm_restrictedmem_invalidate_begin(struct restrictedmem_notifier *notifier,
> + pgoff_t start, pgoff_t end)
> +{
> + struct kvm_memory_slot *slot = container_of(notifier,
> + struct kvm_memory_slot,
> + notifier);
> + struct kvm *kvm = slot->kvm;
> + gfn_t gfn_start, gfn_end;
> + struct kvm_gfn_range gfn_range;
> + int idx;
> +
> + if (!restrictedmem_range_is_valid(slot, start, end,
> + &gfn_start, &gfn_end))
> + return;
> +
> + idx = srcu_read_lock(&kvm->srcu);
> + KVM_MMU_LOCK(kvm);
> +
> + kvm_mmu_invalidate_begin(kvm, gfn_start, gfn_end);
> +
> + gfn_range.start = gfn_start;
> + gfn_range.end = gfn_end;
> + gfn_range.slot = slot;
> + gfn_range.pte = __pte(0);
> + gfn_range.may_block = true;
> +
> + if (kvm_unmap_gfn_range(kvm, &gfn_range))
> + kvm_flush_remote_tlbs(kvm);
> +
> + KVM_MMU_UNLOCK(kvm);
> + srcu_read_unlock(&kvm->srcu, idx);
> +}
> +
> +static void kvm_restrictedmem_invalidate_end(struct restrictedmem_notifier *notifier,
> + pgoff_t start, pgoff_t end)
> +{
> + struct kvm_memory_slot *slot = container_of(notifier,
> + struct kvm_memory_slot,
> + notifier);
> + struct kvm *kvm = slot->kvm;
> + gfn_t gfn_start, gfn_end;
> +
> + if (!restrictedmem_range_is_valid(slot, start, end,
> + &gfn_start, &gfn_end))
> + return;
> +
> + KVM_MMU_LOCK(kvm);
> + kvm_mmu_invalidate_end(kvm, gfn_start, gfn_end);
> + KVM_MMU_UNLOCK(kvm);
> +}
> +
> +static struct restrictedmem_notifier_ops kvm_restrictedmem_notifier_ops = {
> + .invalidate_start = kvm_restrictedmem_invalidate_begin,
> + .invalidate_end = kvm_restrictedmem_invalidate_end,
> +};
> +
> +static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)
> +{
> + slot->notifier.ops = &kvm_restrictedmem_notifier_ops;
> + restrictedmem_register_notifier(slot->restricted_file, &slot->notifier);
> +}
> +
> +static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
> +{
> + restrictedmem_unregister_notifier(slot->restricted_file,
> + &slot->notifier);
> +}
> +
> +#else /* !CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
> +static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)
> +{
> + WARN_ON_ONCE(1);
> +}
> +
> +static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
> +{
> + WARN_ON_ONCE(1);
> +}
> +
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
> #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
> static int kvm_pm_notifier_call(struct notifier_block *bl,
> unsigned long state,
> @@ -1072,6 +1177,11 @@ 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_restrictedmem_unregister(slot);
> + fput(slot->restricted_file);
> + }
> +
> kvm_destroy_dirty_bitmap(slot);
>
> kvm_arch_free_memslot(kvm, slot);
> @@ -1643,10 +1753,16 @@ 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_KVM_GENERIC_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
> @@ -1722,6 +1838,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
> {
> int r;
>
> + if (change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
> + kvm_restrictedmem_register(new);
> +
> /*
> * If dirty logging is disabled, nullify the bitmap; the old bitmap
> * will be freed on "commit". If logging is enabled in both old and
> @@ -1750,6 +1869,9 @@ 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_restrictedmem_unregister(new);
> +
> return r;
> }
>
> @@ -2047,7 +2169,7 @@ 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;
>
> @@ -2066,6 +2188,10 @@ 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->restricted_offset & (PAGE_SIZE - 1) ||
> + mem->restricted_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)
> @@ -2104,6 +2230,9 @@ 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))
> @@ -2132,10 +2261,28 @@ 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->restricted_file = fget(mem->restricted_fd);
> + if (!new->restricted_file ||
> + !file_is_restrictedmem(new->restricted_file)) {
> + r = -EINVAL;
> + goto out;
> + }
> + new->restricted_offset = mem->restricted_offset;
> + }
> +
> + new->kvm = kvm;
>
> r = kvm_set_memslot(kvm, old, new, change);
> if (r)
> - kfree(new);
> + goto out;
> +
> + return 0;
> +
> +out:
> + if (new->restricted_file)
> + fput(new->restricted_file);
> + kfree(new);
> return r;
> }
> EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> @@ -4604,6 +4751,11 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
> case KVM_CAP_BINARY_STATS_FD:
> case KVM_CAP_SYSTEM_EVENT_DATA:
> return 1;
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> + case KVM_CAP_PRIVATE_MEM:
> + return 1;
> +#endif
> +
> default:
> break;
> }
> @@ -4795,16 +4947,28 @@ 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 (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
>