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

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Date:   Tue, 4 Sep 2018 15:15:52 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Nikita Leshenko <nikita.leshchenko@...cle.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 Tue, Sep 04, 2018 at 08:37:03AM +0200, Nikita Leshenko wrote:
>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.

Good point! Here is the incremental patch:

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3894,6 +3894,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
                kvm->userspace_pid = task_pid_nr(current);
                current->mm->kvm = kvm;
        } else if (type == KVM_EVENT_DESTROY_VM) {
+               current->mm->kvm = NULL;
                add_uevent_var(env, "EVENT=destroy");
        }
        add_uevent_var(env, "PID=%d", kvm->userspace_pid);

Thanks,
Fengguang