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


From: Chao Peng
Subject: [PATCH v9 8/8] KVM: Enable and expose KVM_MEM_PRIVATE
Date: Tue, 25 Oct 2022 23:13:44 +0800

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(-)

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




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