Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
Date:   Wed, 30 Mar 2022 23:51:00 +0000
From:   David Matlack <dmatlack@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH] KVM: MMU: propagate alloc_workqueue failure
Message-ID: <YkTs5BU24zrw30hK@google.com>
References: <20220330165510.213111-1-pbonzini@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220330165510.213111-1-pbonzini@redhat.com>
Precedence: bulk

On Wed, Mar 30, 2022 at 12:55:10PM -0400, Paolo Bonzini wrote:
> If kvm->arch.tdp_mmu_zap_wq cannot be created, the failure has
> to be propagated up to kvm_mmu_init_vm and kvm_arch_init_vm.
> kvm_arch_init_vm also has to undo all the initialization, so
> group all the MMU initialization code at the beginning and
> handle cleaning up of kvm_page_track_init.
> 

Fixes: 22b94c4b63eb ("KVM: x86/mmu: Zap invalidated roots via asynchronous worker")

> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  2 +-
>  arch/x86/kvm/mmu/mmu.c          | 11 +++++++++--
>  arch/x86/kvm/mmu/tdp_mmu.c      | 17 ++++++++++-------
>  arch/x86/kvm/mmu/tdp_mmu.h      |  4 ++--
>  arch/x86/kvm/x86.c              | 15 ++++++++++-----
>  5 files changed, 32 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 0ddc2e67a731..469c7702fad9 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1584,7 +1584,7 @@ void kvm_mmu_module_exit(void);
>  
>  void kvm_mmu_destroy(struct kvm_vcpu *vcpu);
>  int kvm_mmu_create(struct kvm_vcpu *vcpu);
> -void kvm_mmu_init_vm(struct kvm *kvm);
> +int kvm_mmu_init_vm(struct kvm *kvm);
>  void kvm_mmu_uninit_vm(struct kvm *kvm);
>  
>  void kvm_mmu_after_set_cpuid(struct kvm_vcpu *vcpu);
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 51671cb34fb6..857ba93b5c92 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5768,17 +5768,24 @@ static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm,
>  	kvm_mmu_zap_all_fast(kvm);
>  }
>  
> -void kvm_mmu_init_vm(struct kvm *kvm)
> +int kvm_mmu_init_vm(struct kvm *kvm)
>  {
>  	struct kvm_page_track_notifier_node *node = &kvm->arch.mmu_sp_tracker;
> +	int r;
>  
> +	INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);
> +	INIT_LIST_HEAD(&kvm->arch.zapped_obsolete_pages);
> +	INIT_LIST_HEAD(&kvm->arch.lpage_disallowed_mmu_pages);

I agree with moving these but that should probably be done in a separate
commit.

>  	spin_lock_init(&kvm->arch.mmu_unsync_pages_lock);
>  
> -	kvm_mmu_init_tdp_mmu(kvm);
> +	r = kvm_mmu_init_tdp_mmu(kvm);
> +	if (r < 0)
> +		return r;
>  
>  	node->track_write = kvm_mmu_pte_write;
>  	node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
>  	kvm_page_track_register_notifier(kvm, node);
> +	return 0;
>  }
>  
>  void kvm_mmu_uninit_vm(struct kvm *kvm)
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index e7e7876251b3..d7c112a29fe9 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -14,21 +14,24 @@ static bool __read_mostly tdp_mmu_enabled = true;
>  module_param_named(tdp_mmu, tdp_mmu_enabled, bool, 0644);
>  
>  /* Initializes the TDP MMU for the VM, if enabled. */
> -bool kvm_mmu_init_tdp_mmu(struct kvm *kvm)
> +int kvm_mmu_init_tdp_mmu(struct kvm *kvm)
>  {
> +	struct workqueue_struct *wq;
> +
>  	if (!tdp_enabled || !READ_ONCE(tdp_mmu_enabled))
> -		return false;
> +		return 0;
> +
> +	wq = alloc_workqueue("kvm", WQ_UNBOUND|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE, 0);
> +	if (IS_ERR(wq))
> +		return PTR_ERR(wq);
>  
>  	/* This should not be changed for the lifetime of the VM. */
>  	kvm->arch.tdp_mmu_enabled = true;
> -
>  	INIT_LIST_HEAD(&kvm->arch.tdp_mmu_roots);
>  	spin_lock_init(&kvm->arch.tdp_mmu_pages_lock);
>  	INIT_LIST_HEAD(&kvm->arch.tdp_mmu_pages);
> -	kvm->arch.tdp_mmu_zap_wq =
> -		alloc_workqueue("kvm", WQ_UNBOUND|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE, 0);
> -
> -	return true;
> +	kvm->arch.tdp_mmu_zap_wq = wq;

Suggest moving this to just after checking the return value of
alloc_workqueue().

> +	return 1;

Perhaps return 0 until we have a reason to differentiate the 2 cases.

>  }
>  
>  /* Arbitrarily returns true so that this may be used in if statements. */
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> index 5e5ef2576c81..647926541e38 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.h
> +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> @@ -72,7 +72,7 @@ u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr,
>  					u64 *spte);
>  
>  #ifdef CONFIG_X86_64
> -bool kvm_mmu_init_tdp_mmu(struct kvm *kvm);
> +int kvm_mmu_init_tdp_mmu(struct kvm *kvm);
>  void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
>  static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return sp->tdp_mmu_page; }
>  
> @@ -93,7 +93,7 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu)
>  	return sp && is_tdp_mmu_page(sp) && sp->root_count;
>  }
>  #else
> -static inline bool kvm_mmu_init_tdp_mmu(struct kvm *kvm) { return false; }
> +static inline int kvm_mmu_init_tdp_mmu(struct kvm *kvm) { return 0; }
>  static inline void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm) {}
>  static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return false; }
>  static inline bool is_tdp_mmu(struct kvm_mmu *mmu) { return false; }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fe2171b11441..89b6efb7f504 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11629,12 +11629,13 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  
>  	ret = kvm_page_track_init(kvm);
>  	if (ret)
> -		return ret;
> +		goto out;

nit: This goto is unnecessary.

> +
> +	ret = kvm_mmu_init_vm(kvm);
> +	if (ret)
> +		goto out_page_track;
>  
>  	INIT_HLIST_HEAD(&kvm->arch.mask_notifier_list);
> -	INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);
> -	INIT_LIST_HEAD(&kvm->arch.zapped_obsolete_pages);
> -	INIT_LIST_HEAD(&kvm->arch.lpage_disallowed_mmu_pages);
>  	INIT_LIST_HEAD(&kvm->arch.assigned_dev_head);
>  	atomic_set(&kvm->arch.noncoherent_dma_count, 0);
>  
> @@ -11666,10 +11667,14 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  
>  	kvm_apicv_init(kvm);
>  	kvm_hv_init_vm(kvm);
> -	kvm_mmu_init_vm(kvm);
>  	kvm_xen_init_vm(kvm);
>  
>  	return static_call(kvm_x86_vm_init)(kvm);
> +
> +out_page_track:
> +	kvm_page_track_cleanup(kvm);
> +out:
> +	return ret;
>  }
>  
>  int kvm_arch_post_init_vm(struct kvm *kvm)
> -- 
> 2.31.1
>