Re: [PATCH v9 5/8] KVM: Register/unregister the guest private memory regions

[Yuan Yao <yuan.yao@linux.intel.com>]

On Tue, Oct 25, 2022 at 11:13:41PM +0800, Chao Peng wrote:
> Introduce generic private memory register/unregister by reusing existing
> SEV ioctls KVM_MEMORY_ENCRYPT_{UN,}REG_REGION. It differs from SEV case
> by treating address in the region as gpa instead of hva. Which cases
> should these ioctls go is determined by the kvm_arch_has_private_mem().
> Architecture which supports KVM_PRIVATE_MEM should override this function.
>
> KVM internally defaults all guest memory as private memory and maintain
> the shared memory in 'mem_attr_array'. The above ioctls operate on this
> field and unmap existing mappings if any.
>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  Documentation/virt/kvm/api.rst |  17 ++-
>  arch/x86/kvm/Kconfig           |   1 +
>  include/linux/kvm_host.h       |  10 +-
>  virt/kvm/Kconfig               |   4 +
>  virt/kvm/kvm_main.c            | 227 +++++++++++++++++++++++++--------
>  5 files changed, 198 insertions(+), 61 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 975688912b8c..08253cf498d1 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -4717,10 +4717,19 @@ Documentation/virt/kvm/x86/amd-memory-encryption.rst.
>  This ioctl can be used to register a guest memory region which may
>  contain encrypted data (e.g. guest RAM, SMRAM etc).
>
> -It is used in the SEV-enabled guest. When encryption is enabled, a guest
> -memory region may contain encrypted data. The SEV memory encryption
> -engine uses a tweak such that two identical plaintext pages, each at
> -different locations will have differing ciphertexts. So swapping or
> +Currently this ioctl supports registering memory regions for two usages:
> +private memory and SEV-encrypted memory.
> +
> +When private memory is enabled, this ioctl is used to register guest private
> +memory region and the addr/size of kvm_enc_region represents guest physical
> +address (GPA). In this usage, this ioctl zaps the existing guest memory
> +mappings in KVM that fallen into the region.
> +
> +When SEV-encrypted memory is enabled, this ioctl is used to register guest
> +memory region which may contain encrypted data for a SEV-enabled guest. The
> +addr/size of kvm_enc_region represents userspace address (HVA). The SEV
> +memory encryption engine uses a tweak such that two identical plaintext pages,
> +each at different locations will have differing ciphertexts. So swapping or
>  moving ciphertext of those pages will not result in plaintext being
>  swapped. So relocating (or migrating) physical backing pages for the SEV
>  guest will require some additional steps.
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 8d2bd455c0cd..73fdfa429b20 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -51,6 +51,7 @@ config KVM
>  	select HAVE_KVM_PM_NOTIFIER if PM
>  	select HAVE_KVM_RESTRICTED_MEM if X86_64
>  	select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM
> +	select KVM_GENERIC_PRIVATE_MEM if HAVE_KVM_RESTRICTED_MEM
>  	help
>  	  Support hosting fully virtualized guest machines using hardware
>  	  virtualization extensions.  You will need a fairly recent
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 79e5cbc35fcf..4ce98fa0153c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -245,7 +245,8 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
>  #endif
>
> -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> +
> +#if defined(KVM_ARCH_WANT_MMU_NOTIFIER) || defined(CONFIG_KVM_GENERIC_PRIVATE_MEM)
>  struct kvm_gfn_range {
>  	struct kvm_memory_slot *slot;
>  	gfn_t start;
> @@ -254,6 +255,9 @@ struct kvm_gfn_range {
>  	bool may_block;
>  };
>  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> +#endif
> +
> +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
>  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
>  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
>  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> @@ -794,6 +798,9 @@ struct kvm {
>  	struct notifier_block pm_notifier;
>  #endif
>  	char stats_id[KVM_STATS_NAME_SIZE];
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> +	struct xarray mem_attr_array;
> +#endif
>  };
>
>  #define kvm_err(fmt, ...) \
> @@ -1453,6 +1460,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
>  int kvm_arch_post_init_vm(struct kvm *kvm);
>  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
>  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> +bool kvm_arch_has_private_mem(struct kvm *kvm);
>
>  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
>  /*
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 9ff164c7e0cc..69ca59e82149 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -89,3 +89,7 @@ config HAVE_KVM_PM_NOTIFIER
>
>  config HAVE_KVM_RESTRICTED_MEM
>         bool
> +
> +config KVM_GENERIC_PRIVATE_MEM
> +       bool
> +       depends on HAVE_KVM_RESTRICTED_MEM
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 09c9cdeb773c..fc3835826ace 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
>  }
>  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
>
> +static inline void update_invalidate_range(struct kvm *kvm, gfn_t start,
> +							    gfn_t end)
> +{
> +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> +		kvm->mmu_invalidate_range_start = start;
> +		kvm->mmu_invalidate_range_end = end;
> +	} else {
> +		/*
> +		 * Fully tracking multiple concurrent ranges has diminishing
> +		 * returns. Keep things simple and just find the minimal range
> +		 * which includes the current and new ranges. As there won't be
> +		 * enough information to subtract a range after its invalidate
> +		 * completes, any ranges invalidated concurrently will
> +		 * accumulate and persist until all outstanding invalidates
> +		 * complete.
> +		 */
> +		kvm->mmu_invalidate_range_start =
> +			min(kvm->mmu_invalidate_range_start, start);
> +		kvm->mmu_invalidate_range_end =
> +			max(kvm->mmu_invalidate_range_end, end);
> +	}
> +}
> +
> +static void mark_invalidate_in_progress(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	/*
> +	 * The count increase must become visible at unlock time as no
> +	 * spte can be established without taking the mmu_lock and
> +	 * count is also read inside the mmu_lock critical section.
> +	 */
> +	kvm->mmu_invalidate_in_progress++;
> +}
> +
> +void kvm_mmu_invalidate_begin(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	mark_invalidate_in_progress(kvm, start, end);
> +	update_invalidate_range(kvm, start, end);
> +}
> +
> +void kvm_mmu_invalidate_end(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	/*
> +	 * This sequence increase will notify the kvm page fault that
> +	 * the page that is going to be mapped in the spte could have
> +	 * been freed.
> +	 */
> +	kvm->mmu_invalidate_seq++;
> +	smp_wmb();
> +	/*
> +	 * The above sequence increase must be visible before the
> +	 * below count decrease, which is ensured by the smp_wmb above
> +	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> +	 */
> +	kvm->mmu_invalidate_in_progress--;
> +}
> +
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
>  {
> @@ -715,51 +771,12 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
>  	kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
>  }
>
> -static inline void update_invalidate_range(struct kvm *kvm, gfn_t start,
> -							    gfn_t end)
> -{
> -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> -		kvm->mmu_invalidate_range_start = start;
> -		kvm->mmu_invalidate_range_end = end;
> -	} else {
> -		/*
> -		 * Fully tracking multiple concurrent ranges has diminishing
> -		 * returns. Keep things simple and just find the minimal range
> -		 * which includes the current and new ranges. As there won't be
> -		 * enough information to subtract a range after its invalidate
> -		 * completes, any ranges invalidated concurrently will
> -		 * accumulate and persist until all outstanding invalidates
> -		 * complete.
> -		 */
> -		kvm->mmu_invalidate_range_start =
> -			min(kvm->mmu_invalidate_range_start, start);
> -		kvm->mmu_invalidate_range_end =
> -			max(kvm->mmu_invalidate_range_end, end);
> -	}
> -}
> -
> -static void mark_invalidate_in_progress(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> -	/*
> -	 * The count increase must become visible at unlock time as no
> -	 * spte can be established without taking the mmu_lock and
> -	 * count is also read inside the mmu_lock critical section.
> -	 */
> -	kvm->mmu_invalidate_in_progress++;
> -}
> -
>  static bool kvm_mmu_handle_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>  {
>  	update_invalidate_range(kvm, range->start, range->end);
>  	return kvm_unmap_gfn_range(kvm, range);
>  }
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> -	mark_invalidate_in_progress(kvm, start, end);
> -	update_invalidate_range(kvm, start, end);
> -}
> -
>  static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>  					const struct mmu_notifier_range *range)
>  {
> @@ -807,23 +824,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>  	return 0;
>  }
>
> -void kvm_mmu_invalidate_end(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> -	/*
> -	 * This sequence increase will notify the kvm page fault that
> -	 * the page that is going to be mapped in the spte could have
> -	 * been freed.
> -	 */
> -	kvm->mmu_invalidate_seq++;
> -	smp_wmb();
> -	/*
> -	 * The above sequence increase must be visible before the
> -	 * below count decrease, which is ensured by the smp_wmb above
> -	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> -	 */
> -	kvm->mmu_invalidate_in_progress--;
> -}
> -
>  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
>  					const struct mmu_notifier_range *range)
>  {
> @@ -937,6 +937,89 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
>
>  #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
>
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> +
> +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	struct kvm_gfn_range gfn_range;
> +	struct kvm_memory_slot *slot;
> +	struct kvm_memslots *slots;
> +	struct kvm_memslot_iter iter;
> +	int i;
> +	int r = 0;
> +
> +	gfn_range.pte = __pte(0);
> +	gfn_range.may_block = true;
> +
> +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +		slots = __kvm_memslots(kvm, i);
> +
> +		kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> +			slot = iter.slot;
> +			gfn_range.start = max(start, slot->base_gfn);
> +			gfn_range.end = min(end, slot->base_gfn + slot->npages);
> +			if (gfn_range.start >= gfn_range.end)
> +				continue;
> +			gfn_range.slot = slot;
> +
> +			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> +		}
> +	}
> +
> +	if (r)
> +		kvm_flush_remote_tlbs(kvm);
> +}
> +
> +#define KVM_MEM_ATTR_SHARED	0x0001
> +static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> +				     bool is_private)
> +{
> +	gfn_t start, end;
> +	unsigned long i;
> +	void *entry;
> +	int idx;
> +	int r = 0;
> +
> +	if (size == 0 || gpa + size < gpa)
> +		return -EINVAL;
> +	if (gpa & (PAGE_SIZE - 1) || size & (PAGE_SIZE - 1))
> +		return -EINVAL;
> +
> +	start = gpa >> PAGE_SHIFT;
> +	end = (gpa + size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> +
> +	/*
> +	 * Guest memory defaults to private, kvm->mem_attr_array only stores
> +	 * shared memory.
> +	 */
> +	entry = is_private ? NULL : xa_mk_value(KVM_MEM_ATTR_SHARED);
> +
> +	idx = srcu_read_lock(&kvm->srcu);
> +	KVM_MMU_LOCK(kvm);
> +	kvm_mmu_invalidate_begin(kvm, start, end);
> +
> +	for (i = start; i < end; i++) {
> +		r = xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> +				    GFP_KERNEL_ACCOUNT));
> +		if (r)
> +			goto err;
> +	}
> +
> +	kvm_unmap_mem_range(kvm, start, end);

lock is hold by KVM_MMU_LOCK() so how about do
kvm_mmu_invalidate_begin() after changing xarray:

kvm_mmu_invalidate_begin(kvm, start, end);
kvm_unmap_mem_range(kvm, start, end);
kvm_mmu_invalidate_end(kvm, start, end);

Also the error handling path doesn't need to care it yet.

> +
> +	goto ret;
> +err:
> +	for (; i > start; i--)
> +		xa_erase(&kvm->mem_attr_array, i);

the start should be covered yet, consider the i is
unsigned long and case of start is 0, may need another
variable j for this.

> +ret:
> +	kvm_mmu_invalidate_end(kvm, start, end);
> +	KVM_MMU_UNLOCK(kvm);
> +	srcu_read_unlock(&kvm->srcu, idx);
> +
> +	return r;
> +}
> +#endif /* CONFIG_KVM_GENERIC_PRIVATE_MEM */
> +
>  #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
>  static int kvm_pm_notifier_call(struct notifier_block *bl,
>  				unsigned long state,
> @@ -1165,6 +1248,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>  	spin_lock_init(&kvm->mn_invalidate_lock);
>  	rcuwait_init(&kvm->mn_memslots_update_rcuwait);
>  	xa_init(&kvm->vcpu_array);
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> +	xa_init(&kvm->mem_attr_array);
> +#endif
>
>  	INIT_LIST_HEAD(&kvm->gpc_list);
>  	spin_lock_init(&kvm->gpc_lock);
> @@ -1338,6 +1424,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
>  		kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
>  		kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
>  	}
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> +	xa_destroy(&kvm->mem_attr_array);
> +#endif
>  	cleanup_srcu_struct(&kvm->irq_srcu);
>  	cleanup_srcu_struct(&kvm->srcu);
>  	kvm_arch_free_vm(kvm);
> @@ -1541,6 +1630,11 @@ static void kvm_replace_memslot(struct kvm *kvm,
>  	}
>  }
>
> +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)
>  {
>  	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> @@ -4708,6 +4802,24 @@ static long kvm_vm_ioctl(struct file *filp,
>  		r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
>  		break;
>  	}
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> +	case KVM_MEMORY_ENCRYPT_REG_REGION:
> +	case KVM_MEMORY_ENCRYPT_UNREG_REGION: {
> +		struct kvm_enc_region region;
> +		bool set = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION;
> +
> +		if (!kvm_arch_has_private_mem(kvm))
> +			goto arch_vm_ioctl;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&region, argp, sizeof(region)))
> +			goto out;
> +
> +		r = kvm_vm_ioctl_set_mem_attr(kvm, region.addr,
> +					      region.size, set);
> +		break;
> +	}
> +#endif
>  	case KVM_GET_DIRTY_LOG: {
>  		struct kvm_dirty_log log;
>
> @@ -4861,6 +4973,9 @@ static long kvm_vm_ioctl(struct file *filp,
>  		r = kvm_vm_ioctl_get_stats_fd(kvm);
>  		break;
>  	default:
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> +arch_vm_ioctl:
> +#endif
>  		r = kvm_arch_vm_ioctl(filp, ioctl, arg);
>  	}
>  out:
> --
> 2.25.1
>
>