linux-kernel - Re: [RFC][PATCH 1/5] [PATCH 1/5] kvm: register in task

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Date:   Tue, 4 Sep 2018 08:37:03 +0200
From:   Nikita Leshenko <nikita.leshchenko@...cle.com>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        dongx.peng@...el.com, jingqi.liu@...el.com, eddie.dong@...el.com,
        dave.hansen@...el.com, ying.huang@...el.com, bgregg@...flix.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 1/5] [PATCH 1/5] kvm: register in task_struct

On 4 Sep 2018, at 2:46, Fengguang Wu <fengguang.wu@...el.com> wrote:
> 
> Here it goes:
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 99ce070e7dcb..27c5446f3deb 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -27,6 +27,7 @@ typedef int vm_fault_t;
> struct address_space;
> struct mem_cgroup;
> struct hmm;
> +struct kvm;
> /*
> * Each physical page in the system has a struct page associated with
> @@ -489,10 +490,19 @@ struct mm_struct {
> 	/* HMM needs to track a few things per mm */
> 	struct hmm *hmm;
> #endif
> +#if IS_ENABLED(CONFIG_KVM)
> +	struct kvm *kvm;
> +#endif
> } __randomize_layout;
> extern struct mm_struct init_mm;
> +#if IS_ENABLED(CONFIG_KVM)
> +static inline struct kvm *mm_kvm(struct mm_struct *mm) { return mm->kvm; }
> +#else
> +static inline struct kvm *mm_kvm(struct mm_struct *mm) { return NULL; }
> +#endif
> +
> static inline void mm_init_cpumask(struct mm_struct *mm)
> {
> #ifdef CONFIG_CPUMASK_OFFSTACK
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 0c483720de8d..dca6156a7b35 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3892,7 +3892,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
> 	if (type == KVM_EVENT_CREATE_VM) {
> 		add_uevent_var(env, "EVENT=create");
> 		kvm->userspace_pid = task_pid_nr(current);
> -		current->kvm = kvm;
> +		current->mm->kvm = kvm;
I think you also need to reset kvm to NULL once the VM is
destroyed, otherwise it would point to dangling memory.

-Nikita
> 	} else if (type == KVM_EVENT_DESTROY_VM) {
> 		add_uevent_var(env, "EVENT=destroy");
> 	}