Re: [RFC PATCH 4/5] KVM: TDX: Implement moving private pages between 2 TDs

[Isaku Yamahata]

On Fri, Apr 07, 2023 at 08:19:20PM +0000,
Sagi Shahar <sagis@xxxxxxxxxx> wrote:

> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 327dee4f6170e..685528fdc0ad6 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -296,6 +296,23 @@ static void tdp_mmu_init_sp(struct kvm_mmu_page *sp, tdp_ptep_t sptep,
>  	trace_kvm_mmu_get_page(sp, true);
>  }
>  
> +static struct kvm_mmu_page *
> +kvm_tdp_mmu_get_vcpu_root_no_alloc(struct kvm_vcpu *vcpu, union kvm_mmu_page_role role)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm_mmu_page *root;
> +
> +	lockdep_assert_held_read(&kvm->mmu_lock);

Because kvm_tdp_mmu_get_cpu_root() holds write lock, 
this should be lockdep_assert_held(&kvm->mmu_lock)

Thanks,

> +
> +	for_each_tdp_mmu_root(kvm, root, kvm_mmu_role_as_id(role)) {
> +		if (root->role.word == role.word &&
> +		    kvm_tdp_mmu_get_root(root))
> +			return root;
> +	}
> +
> +	return NULL;
> +}
> +
>  static struct kvm_mmu_page *kvm_tdp_mmu_get_vcpu_root(struct kvm_vcpu *vcpu,
>  						      bool private)
>  {
> @@ -311,11 +328,9 @@ static struct kvm_mmu_page *kvm_tdp_mmu_get_vcpu_root(struct kvm_vcpu *vcpu,
>  	 */
>  	if (private)
>  		kvm_mmu_page_role_set_private(&role);
> -	for_each_tdp_mmu_root(kvm, root, kvm_mmu_role_as_id(role)) {
> -		if (root->role.word == role.word &&
> -		    kvm_tdp_mmu_get_root(root))
> -			goto out;
> -	}
> +	root = kvm_tdp_mmu_get_vcpu_root_no_alloc(vcpu, role);
> +	if (!!root)
> +		goto out;
>  
>  	root = tdp_mmu_alloc_sp(vcpu, role);
>  	tdp_mmu_init_sp(root, NULL, 0);
> @@ -330,6 +345,58 @@ static struct kvm_mmu_page *kvm_tdp_mmu_get_vcpu_root(struct kvm_vcpu *vcpu,
>  	return root;
>  }
>  
> +hpa_t kvm_tdp_mmu_move_private_pages_from(struct kvm_vcpu *vcpu,
> +					  struct kvm_vcpu *src_vcpu)
> +{
> +	union kvm_mmu_page_role role = vcpu->arch.mmu->root_role;
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm *src_kvm = src_vcpu->kvm;
> +	struct kvm_mmu_page *private_root = NULL;
> +	struct kvm_mmu_page *root;
> +	s64 num_private_pages, old;
> +
> +	lockdep_assert_held_write(&vcpu->kvm->mmu_lock);
> +	lockdep_assert_held_write(&src_vcpu->kvm->mmu_lock);
> +
> +	/* Find the private root of the source. */
> +	kvm_mmu_page_role_set_private(&role);
> +	for_each_tdp_mmu_root(src_kvm, root, kvm_mmu_role_as_id(role)) {
> +		if (root->role.word == role.word) {
> +			private_root = root;
> +			break;
> +		}
> +	}
> +	if (!private_root)
> +		return INVALID_PAGE;
> +
> +	/* Remove the private root from the src kvm and add it to dst kvm. */
> +	list_del_rcu(&private_root->link);
> +	list_add_rcu(&private_root->link, &kvm->arch.tdp_mmu_roots);
> +
> +	num_private_pages = atomic64_read(&src_kvm->arch.tdp_private_mmu_pages);
> +	old = atomic64_cmpxchg(&kvm->arch.tdp_private_mmu_pages, 0,
> +			       num_private_pages);
> +	/* The destination VM should have no private pages at this point. */
> +	WARN_ON(old);
> +	atomic64_set(&src_kvm->arch.tdp_private_mmu_pages, 0);
> +
> +	return __pa(private_root->spt);
> +}
> +
> +hpa_t kvm_tdp_mmu_get_vcpu_root_hpa_no_alloc(struct kvm_vcpu *vcpu, bool private)
> +{
> +	struct kvm_mmu_page *root;
> +	union kvm_mmu_page_role role = vcpu->arch.mmu->root_role;
> +
> +	if (private)
> +		kvm_mmu_page_role_set_private(&role);
> +	root = kvm_tdp_mmu_get_vcpu_root_no_alloc(vcpu, role);
> +	if (!root)
> +		return INVALID_PAGE;
> +
> +	return __pa(root->spt);
> +}
> +
>  hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu, bool private)
>  {
>  	return __pa(kvm_tdp_mmu_get_vcpu_root(vcpu, private)->spt);

-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>