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

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Date:   Tue, 4 Sep 2018 08:46:21 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Nikita Leshenko <nikita.leshchenko@...cle.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 08:28:18AM +0800, Fengguang Wu wrote:
>Hi Christian and Nikita,
>
>On Mon, Sep 03, 2018 at 06:03:49PM +0200, Christian Borntraeger wrote:
>>
>>
>>On 09/03/2018 04:10 PM, Nikita Leshenko wrote:
>>> On September 2, 2018 5:21:15 AM, fengguang.wu@...el.com wrote:
>>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>>>> index 8b47507faab5..0c483720de8d 100644
>>>> --- a/virt/kvm/kvm_main.c
>>>> +++ b/virt/kvm/kvm_main.c
>>>> @@ -3892,6 +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;
>>>
>>> Is it OK to store `kvm` on the task_struct? What if the thread that
>>> originally created the VM exits? From the documentation it seems
>>> like a VM is associated with an address space and not a specific
>>> thread, so maybe it should be stored on mm_struct?
>>
>>Yes, ioctls accessing the kvm can happen from all threads.
>
>Good point, thank you for the tips! I'll move kvm pointer to mm_struct.
>
>>> From Documentation/virtual/kvm/api.txt:
>>>    Only run VM ioctls from the same process (address space) that was used
>>>    to create the VM.
>>>
>>> -Nikita

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