Re: [RFC PATCH 2/5] KVM: SEV: Refactor common code out of sev_vm_move_enc_context_from

[Zhi Wang <zhi.wang.linux@gmail.com>]

On Fri,  7 Apr 2023 20:19:18 +0000
Sagi Shahar <sagis@google.com> wrote:

> Both SEV and TDX are going to use similar flows for intra-host
> migration. This change moves some of the code which will be used by both
> architecture into shared code in x86.h
> 
> Signed-off-by: Sagi Shahar <sagis@google.com>
> ---
>  arch/x86/kvm/svm/sev.c | 175 +++++------------------------------------
>  arch/x86/kvm/x86.c     | 166 ++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/x86.h     |  16 ++++
>  3 files changed, 201 insertions(+), 156 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index c25aeb550cd97..18831a0b7734e 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1553,116 +1553,6 @@ static bool is_cmd_allowed_from_mirror(u32 cmd_id)
>  	return false;
>  }
>  
> -static int sev_lock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
> -{
> -	struct kvm_sev_info *dst_sev = &to_kvm_svm(dst_kvm)->sev_info;
> -	struct kvm_sev_info *src_sev = &to_kvm_svm(src_kvm)->sev_info;
> -	int r = -EBUSY;
> -
> -	if (dst_kvm == src_kvm)
> -		return -EINVAL;
> -
> -	/*
> -	 * Bail if these VMs are already involved in a migration to avoid
> -	 * deadlock between two VMs trying to migrate to/from each other.
> -	 */
> -	if (atomic_cmpxchg_acquire(&dst_sev->migration_in_progress, 0, 1))
> -		return -EBUSY;
> -
> -	if (atomic_cmpxchg_acquire(&src_sev->migration_in_progress, 0, 1))
> -		goto release_dst;
> -
> -	r = -EINTR;
> -	if (mutex_lock_killable(&dst_kvm->lock))
> -		goto release_src;
> -	if (mutex_lock_killable_nested(&src_kvm->lock, SINGLE_DEPTH_NESTING))
> -		goto unlock_dst;
> -	return 0;
> -
> -unlock_dst:
> -	mutex_unlock(&dst_kvm->lock);
> -release_src:
> -	atomic_set_release(&src_sev->migration_in_progress, 0);
> -release_dst:
> -	atomic_set_release(&dst_sev->migration_in_progress, 0);
> -	return r;
> -}
> -
> -static void sev_unlock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
> -{
> -	struct kvm_sev_info *dst_sev = &to_kvm_svm(dst_kvm)->sev_info;
> -	struct kvm_sev_info *src_sev = &to_kvm_svm(src_kvm)->sev_info;
> -
> -	mutex_unlock(&dst_kvm->lock);
> -	mutex_unlock(&src_kvm->lock);
> -	atomic_set_release(&dst_sev->migration_in_progress, 0);
> -	atomic_set_release(&src_sev->migration_in_progress, 0);
> -}
> -
> -/* vCPU mutex subclasses.  */
> -enum sev_migration_role {
> -	SEV_MIGRATION_SOURCE = 0,
> -	SEV_MIGRATION_TARGET,
> -	SEV_NR_MIGRATION_ROLES,
> -};
> -
> -static int sev_lock_vcpus_for_migration(struct kvm *kvm,
> -					enum sev_migration_role role)
> -{
> -	struct kvm_vcpu *vcpu;
> -	unsigned long i, j;
> -
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		if (mutex_lock_killable_nested(&vcpu->mutex, role))
> -			goto out_unlock;
> -
> -#ifdef CONFIG_PROVE_LOCKING
> -		if (!i)
> -			/*
> -			 * Reset the role to one that avoids colliding with
> -			 * the role used for the first vcpu mutex.
> -			 */
> -			role = SEV_NR_MIGRATION_ROLES;
> -		else
> -			mutex_release(&vcpu->mutex.dep_map, _THIS_IP_);
> -#endif
> -	}
> -
> -	return 0;
> -
> -out_unlock:
> -
> -	kvm_for_each_vcpu(j, vcpu, kvm) {
> -		if (i == j)
> -			break;
> -
> -#ifdef CONFIG_PROVE_LOCKING
> -		if (j)
> -			mutex_acquire(&vcpu->mutex.dep_map, role, 0, _THIS_IP_);
> -#endif
> -
> -		mutex_unlock(&vcpu->mutex);
> -	}
> -	return -EINTR;
> -}
> -
> -static void sev_unlock_vcpus_for_migration(struct kvm *kvm)
> -{
> -	struct kvm_vcpu *vcpu;
> -	unsigned long i;
> -	bool first = true;
> -
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		if (first)
> -			first = false;
> -		else
> -			mutex_acquire(&vcpu->mutex.dep_map,
> -				      SEV_NR_MIGRATION_ROLES, 0, _THIS_IP_);
> -
> -		mutex_unlock(&vcpu->mutex);
> -	}
> -}
> -
>  static void sev_migrate_from(struct kvm *dst_kvm, struct kvm *src_kvm)
>  {
>  	struct kvm_sev_info *dst = &to_kvm_svm(dst_kvm)->sev_info;
> @@ -1744,25 +1634,6 @@ static void sev_migrate_from(struct kvm *dst_kvm, struct kvm *src_kvm)
>  	}
>  }
>  
> -static int sev_check_source_vcpus(struct kvm *dst, struct kvm *src)
> -{
> -	struct kvm_vcpu *src_vcpu;
> -	unsigned long i;
> -
> -	if (!sev_es_guest(src))
> -		return 0;
> -
> -	if (atomic_read(&src->online_vcpus) != atomic_read(&dst->online_vcpus))
> -		return -EINVAL;
> -
> -	kvm_for_each_vcpu(i, src_vcpu, src) {
> -		if (!src_vcpu->arch.guest_state_protected)
> -			return -EINVAL;
> -	}
> -
> -	return 0;
> -}
> -
>  int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>  {
>  	struct kvm_sev_info *dst_sev = &to_kvm_svm(kvm)->sev_info;
> @@ -1777,19 +1648,20 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>  		ret = -EBADF;
>  		goto out_fput;
>  	}
> -
>  	source_kvm = source_kvm_file->private_data;
> -	ret = sev_lock_two_vms(kvm, source_kvm);
> +	src_sev = &to_kvm_svm(source_kvm)->sev_info;
> +
> +	ret = pre_move_enc_context_from(kvm, source_kvm,
> +					&dst_sev->migration_in_progress,
> +					&src_sev->migration_in_progress);
>  	if (ret)
>  		goto out_fput;
>  
> -	if (sev_guest(kvm) || !sev_guest(source_kvm)) {
> +	if (sev_guest(kvm) || !sev_es_guest(source_kvm)) {
>  		ret = -EINVAL;
> -		goto out_unlock;
> +		goto out_post;
>  	}
>  
> -	src_sev = &to_kvm_svm(source_kvm)->sev_info;
> -
>  	dst_sev->misc_cg = get_current_misc_cg();
>  	cg_cleanup_sev = dst_sev;
>  	if (dst_sev->misc_cg != src_sev->misc_cg) {
> @@ -1799,34 +1671,21 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>  		charged = true;
>  	}
>  
> -	ret = sev_lock_vcpus_for_migration(kvm, SEV_MIGRATION_SOURCE);
> -	if (ret)
> -		goto out_dst_cgroup;
> -	ret = sev_lock_vcpus_for_migration(source_kvm, SEV_MIGRATION_TARGET);
> -	if (ret)
> -		goto out_dst_vcpu;
> -
> -	ret = sev_check_source_vcpus(kvm, source_kvm);
> -	if (ret)
> -		goto out_source_vcpu;
> -
>  	sev_migrate_from(kvm, source_kvm);
>  	kvm_vm_dead(source_kvm);
>  	cg_cleanup_sev = src_sev;
>  	ret = 0;
>  
> -out_source_vcpu:
> -	sev_unlock_vcpus_for_migration(source_kvm);
> -out_dst_vcpu:
> -	sev_unlock_vcpus_for_migration(kvm);
>  out_dst_cgroup:
>  	/* Operates on the source on success, on the destination on failure.  */
>  	if (charged)
>  		sev_misc_cg_uncharge(cg_cleanup_sev);
>  	put_misc_cg(cg_cleanup_sev->misc_cg);
>  	cg_cleanup_sev->misc_cg = NULL;
> -out_unlock:
> -	sev_unlock_two_vms(kvm, source_kvm);
> +out_post:
> +	post_move_enc_context_from(kvm, source_kvm,
> +				   &dst_sev->migration_in_progress,
> +				   &src_sev->migration_in_progress);
>  out_fput:
>  	if (source_kvm_file)
>  		fput(source_kvm_file);
> @@ -2058,7 +1917,11 @@ int sev_vm_copy_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>  	}
>  
>  	source_kvm = source_kvm_file->private_data;
> -	ret = sev_lock_two_vms(kvm, source_kvm);
> +	source_sev = &to_kvm_svm(source_kvm)->sev_info;
> +	mirror_sev = &to_kvm_svm(kvm)->sev_info;
> +	ret = lock_two_vms_for_migration(kvm, source_kvm,
> +					 &mirror_sev->migration_in_progress,
> +					 &source_sev->migration_in_progress);
>  	if (ret)
>  		goto e_source_fput;
>  
> @@ -2078,9 +1941,7 @@ int sev_vm_copy_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>  	 * The mirror kvm holds an enc_context_owner ref so its asid can't
>  	 * disappear until we're done with it
>  	 */
> -	source_sev = &to_kvm_svm(source_kvm)->sev_info;
>  	kvm_get_kvm(source_kvm);
> -	mirror_sev = &to_kvm_svm(kvm)->sev_info;
>  	list_add_tail(&mirror_sev->mirror_entry, &source_sev->mirror_vms);
>  
>  	/* Set enc_context_owner and copy its encryption context over */
> @@ -2101,7 +1962,9 @@ int sev_vm_copy_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>  	 */
>  
>  e_unlock:
> -	sev_unlock_two_vms(kvm, source_kvm);
> +	unlock_two_vms_for_migration(kvm, source_kvm,
> +				     &mirror_sev->migration_in_progress,
> +				     &source_sev->migration_in_progress);
>  e_source_fput:
>  	if (source_kvm_file)
>  		fput(source_kvm_file);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 870041887ed91..865c434a94899 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -13596,6 +13596,172 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
>  }
>  EXPORT_SYMBOL_GPL(kvm_sev_es_string_io);
>  
> +/* vCPU mutex subclasses.  */
> +enum migration_role {
> +	MIGRATION_SOURCE = 0,
> +	MIGRATION_TARGET,
> +	NR_MIGRATION_ROLES,
> +};
> +

> +static int lock_vcpus_for_migration(struct kvm *kvm, enum migration_role role)
> +{
> +	struct kvm_vcpu *vcpu;
> +	unsigned long i, j;
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		if (mutex_lock_killable_nested(&vcpu->mutex, role))
> +			goto out_unlock;
> +
> +#ifdef CONFIG_PROVE_LOCKING
> +		if (!i)
> +			/*
> +			 * Reset the role to one that avoids colliding with
> +			 * the role used for the first vcpu mutex.
> +			 */
> +			role = NR_MIGRATION_ROLES;
> +		else
> +			mutex_release(&vcpu->mutex.dep_map, _THIS_IP_);
> +#endif
> +	}
> +
> +	return 0;
> +
> +out_unlock:
> +
> +	kvm_for_each_vcpu(j, vcpu, kvm) {
> +		if (i == j)
> +			break;
> +
> +#ifdef CONFIG_PROVE_LOCKING
> +		if (j)
> +			mutex_acquire(&vcpu->mutex.dep_map, role, 0, _THIS_IP_);
> +#endif
> +
> +		mutex_unlock(&vcpu->mutex);
> +	}
> +	return -EINTR;
> +}
> +
> +static void unlock_vcpus_for_migration(struct kvm *kvm)
> +{
> +	struct kvm_vcpu *vcpu;
> +	unsigned long i;
> +	bool first = true;
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		if (first)
> +			first = false;
> +		else
> +			mutex_acquire(&vcpu->mutex.dep_map, NR_MIGRATION_ROLES,
> +				      0, _THIS_IP_);
> +
> +		mutex_unlock(&vcpu->mutex);
> +	}
> +}
> +
> +int lock_two_vms_for_migration(struct kvm *dst_kvm, struct kvm *src_kvm,
> +			       atomic_t *dst_migration_in_progress,
> +			       atomic_t *src_migration_in_progress)
> +{
> +	int r = -EBUSY;
> +
> +	if (dst_kvm == src_kvm)
> +		return -EINVAL;
> +
> +	/*
> +	 * Bail if these VMs are already involved in a migration to avoid
> +	 * deadlock between two VMs trying to migrate to/from each other.
> +	 */
> +	if (atomic_cmpxchg_acquire(dst_migration_in_progress, 0, 1))
> +		return -EBUSY;
> +
> +	if (atomic_cmpxchg_acquire(src_migration_in_progress, 0, 1))
> +		goto release_dst;
> +
> +	r = -EINTR;
> +	if (mutex_lock_killable(&dst_kvm->lock))
> +		goto release_src;
> +	if (mutex_lock_killable_nested(&src_kvm->lock, SINGLE_DEPTH_NESTING))
> +		goto unlock_dst;
> +	return 0;
> +
> +unlock_dst:
> +	mutex_unlock(&dst_kvm->lock);
> +release_src:
> +	atomic_set_release(src_migration_in_progress, 0);
> +release_dst:
> +	atomic_set_release(dst_migration_in_progress, 0);
> +	return r;
> +}
> +EXPORT_SYMBOL_GPL(lock_two_vms_for_migration);
> +
> +void unlock_two_vms_for_migration(struct kvm *dst_kvm, struct kvm *src_kvm,
> +				  atomic_t *dst_migration_in_progress,
> +				  atomic_t *src_migration_in_progress)
> +{
> +	mutex_unlock(&dst_kvm->lock);
> +	mutex_unlock(&src_kvm->lock);
> +	atomic_set_release(dst_migration_in_progress, 0);
> +	atomic_set_release(src_migration_in_progress, 0);
> +}
> +EXPORT_SYMBOL_GPL(unlock_two_vms_for_migration);
> +
> +int pre_move_enc_context_from(struct kvm *dst_kvm, struct kvm *src_kvm,
> +			      atomic_t *dst_migration_in_progress,
> +			      atomic_t *src_migration_in_progress)
> +{
> +	struct kvm_vcpu *src_vcpu;
> +	unsigned long i;
> +	int ret = -EINVAL;
> +
> +	ret = lock_two_vms_for_migration(dst_kvm, src_kvm,
> +					 dst_migration_in_progress,
> +					 src_migration_in_progress);
> +	if (ret)
> +		return ret;
> +
> +	ret = lock_vcpus_for_migration(dst_kvm, MIGRATION_TARGET);
> +	if (ret)
> +		goto unlock_vms;
> +
> +	ret = lock_vcpus_for_migration(src_kvm, MIGRATION_SOURCE);
> +	if (ret)
> +		goto unlock_dst_vcpu;
> +
> +	if (atomic_read(&dst_kvm->online_vcpus) !=
> +	    atomic_read(&src_kvm->online_vcpus))
> +		goto unlock_dst_vcpu;
> +
> +	kvm_for_each_vcpu(i, src_vcpu, src_kvm) {
> +		if (!src_vcpu->arch.guest_state_protected)
> +			goto unlock_dst_vcpu;
> +	}
> +
> +	return 0;
> +
> +unlock_dst_vcpu:
> +	unlock_vcpus_for_migration(dst_kvm);
> +unlock_vms:
> +	unlock_two_vms_for_migration(dst_kvm, src_kvm,
> +				     dst_migration_in_progress,
> +				     src_migration_in_progress);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(pre_move_enc_context_from);
> +
> +void post_move_enc_context_from(struct kvm *dst_kvm, struct kvm *src_kvm,
> +				atomic_t *dst_migration_in_progress,
> +				atomic_t *src_migration_in_progress)
> +{
> +	unlock_vcpus_for_migration(src_kvm);
> +	unlock_vcpus_for_migration(dst_kvm);
> +	unlock_two_vms_for_migration(dst_kvm, src_kvm,
> +				     dst_migration_in_progress,
> +				     src_migration_in_progress);
> +}
> +EXPORT_SYMBOL_GPL(post_move_enc_context_from);
> +

It would be nice to have kvm_ prefix for the functions exported.

>  bool kvm_arch_dirty_log_supported(struct kvm *kvm)
>  {
>  	return kvm->arch.vm_type != KVM_X86_PROTECTED_VM;
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 33a1a5341e788..554c797184994 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -502,4 +502,20 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
>  			 unsigned int port, void *data,  unsigned int count,
>  			 int in);
>  
> +int lock_two_vms_for_migration(struct kvm *dst_kvm, struct kvm *src_kvm,
> +			       atomic_t *dst_migration_in_progress,
> +			       atomic_t *src_migration_in_progress);
> +
> +void unlock_two_vms_for_migration(struct kvm *dst_kvm, struct kvm *src_kvm,
> +				  atomic_t *dst_migration_in_progress,
> +				  atomic_t *src_migration_in_progress);
> +
> +int pre_move_enc_context_from(struct kvm *dst_kvm, struct kvm *src_kvm,
> +			      atomic_t *dst_migration_in_progress,
> +			      atomic_t *src_migration_in_progress);
> +
> +void post_move_enc_context_from(struct kvm *dst_kvm, struct kvm *src_kvm,
> +				atomic_t *dst_migration_in_progress,
> +				atomic_t *src_migration_in_progress);
> +
>  #endif