Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

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Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> writes:

Register/unregister private memslot to fd-based memory backing store
restrictedmem and implement the callbacks for restrictedmem_notifier:
   - invalidate_start()/invalidate_end() to zap the existing memory
     mappings in the KVM page table.
   - error() to request KVM_REQ_MEMORY_MCE and later exit to userspace
     with KVM_EXIT_SHUTDOWN.

Expose KVM_MEM_PRIVATE for memslot and KVM_MEMORY_ATTRIBUTE_PRIVATE for
KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to userspace but either are
controlled by kvm_arch_has_private_mem() which should be rewritten by
architecture code.

Could we perhaps rename KVM_MEM_PRIVATE to KVM_MEM_PROTECTED, to be in
line with KVM_X86_PROTECTED_VM?

I feel that a memslot that has the KVM_MEM_PRIVATE flag need not always
be private; It can sometimes be providing memory that is shared and
also accessible from the host.

KVM_MEMORY_ATTRIBUTE_PRIVATE is fine as-is because this flag is set when
the guest memory is meant to be backed by private memory.

KVM_MEMORY_EXIT_FLAG_PRIVATE is also okay because the flag is used to
indicate when the memory error is caused by a private access (as opposed
to a shared access).

kvm_slot_can_be_private() could perhaps be renamed kvm_is_protected_slot()?


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>
Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
---
  arch/x86/include/asm/kvm_host.h |   1 +
  arch/x86/kvm/x86.c              |  13 +++
  include/linux/kvm_host.h        |   3 +
  virt/kvm/kvm_main.c             | 179 +++++++++++++++++++++++++++++++-
  4 files changed, 191 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7772ab37ac89..27ef31133352 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -114,6 +114,7 @@
  	KVM_ARCH_REQ_FLAGS(31, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
  #define KVM_REQ_HV_TLB_FLUSH \
  	KVM_ARCH_REQ_FLAGS(32, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_MEMORY_MCE		KVM_ARCH_REQ(33)

  #define CR0_RESERVED_BITS                                               \
  	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5aefcff614d2..c67e22f3e2ee 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6587,6 +6587,13 @@ int kvm_arch_pm_notifier(struct kvm *kvm, unsigned long state)
  }
  #endif /* CONFIG_HAVE_KVM_PM_NOTIFIER */

+#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
+void kvm_arch_memory_mce(struct kvm *kvm)
+{
+	kvm_make_all_cpus_request(kvm, KVM_REQ_MEMORY_MCE);
+}
+#endif
+
  static int kvm_vm_ioctl_get_clock(struct kvm *kvm, void __user *argp)
  {
  	struct kvm_clock_data data = { 0 };
@@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)

  		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
  			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
+
+		if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
+			vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
+			r = 0;
+			goto out;
+		}
  	}

  	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win ||
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 153842bb33df..f032d878e034 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -590,6 +590,7 @@ 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) @@ -2363,6 +2364,8 @@ static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
  	*pfn = page_to_pfn(page);
  	return ret;
  }
+
+void kvm_arch_memory_mce(struct kvm *kvm);
  #endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */

  #endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e107afea32f0..ac835fc77273 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -936,6 +936,121 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)

  #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */

+#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;
+
+	gfn_range.start = gfn_start;
+	gfn_range.end = gfn_end;
+	gfn_range.slot = slot;
+	gfn_range.pte = __pte(0);
+	gfn_range.may_block = true;
+
+	idx = srcu_read_lock(&kvm->srcu);
+	KVM_MMU_LOCK(kvm);
+
+	kvm_mmu_invalidate_begin(kvm);
+	kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
+	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);
+	KVM_MMU_UNLOCK(kvm);
+}
+
+static void kvm_restrictedmem_error(struct restrictedmem_notifier *notifier,
+				    pgoff_t start, pgoff_t end)
+{
+	struct kvm_memory_slot *slot = container_of(notifier,
+						    struct kvm_memory_slot,
+						    notifier);
+	kvm_arch_memory_mce(slot->kvm);
+}
+
+static struct restrictedmem_notifier_ops kvm_restrictedmem_notifier_ops = {
+	.invalidate_start = kvm_restrictedmem_invalidate_begin,
+	.invalidate_end = kvm_restrictedmem_invalidate_end,
+	.error = kvm_restrictedmem_error,
+};
+
+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,
@@ -980,6 +1095,11 @@ 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);
@@ -1551,10 +1671,14 @@ static void kvm_replace_memslot(struct kvm *kvm,
  	}
  }

-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;

+	if (kvm_arch_has_private_mem(kvm))
+		valid_flags |= KVM_MEM_PRIVATE;
+
  #ifdef __KVM_HAVE_READONLY_MEM
  	valid_flags |= KVM_MEM_READONLY;
  #endif
@@ -1630,6 +1754,9 @@ 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
@@ -1658,6 +1785,9 @@ 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;
  }

@@ -1963,7 +2093,7 @@ 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;

@@ -1982,6 +2112,10 @@ 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)
@@ -2020,6 +2154,9 @@ 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))
@@ -2048,10 +2185,28 @@ 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);
@@ -2351,6 +2506,8 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
  #ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
  static u64 kvm_supported_mem_attributes(struct kvm *kvm)
  {
+	if (kvm_arch_has_private_mem(kvm))
+		return KVM_MEMORY_ATTRIBUTE_PRIVATE;
  	return 0;
  }

@@ -4822,16 +4979,28 @@ 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);



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