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SubjectRe: [RFC][PATCH v2 14/21] kvm: register in mm_struct
On Wed, Dec 26, 2018 at 09:15:00PM +0800, Fengguang Wu wrote:
> VM is associated with an address space and not a specific thread.
>
> >From Documentation/virtual/kvm/api.txt:
> Only run VM ioctls from the same process (address space) that was used
> to create the VM.

Hi, Fengguang,

AFAIU the commit message only explains why a kvm object needs to bind
to a single mm object (say, the reason why there is kvm->mm) however
not the reverse (say, the reason why there is mm->kvm), while the
latter is what this patch really needs?

I'm thinking whether it's legal for multiple VMs to run on a single mm
address space. I don't see a limitation so far but it's very possible
I am just missing something there (if there is, IMHO they might be
something nice to put into the commit message?). Thanks,

>
> CC: Nikita Leshenko <nikita.leshchenko@oracle.com>
> CC: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
> ---
> include/linux/mm_types.h | 11 +++++++++++
> virt/kvm/kvm_main.c | 3 +++
> 2 files changed, 14 insertions(+)
>
> --- linux.orig/include/linux/mm_types.h 2018-12-23 19:58:06.993417137 +0800
> +++ linux/include/linux/mm_types.h 2018-12-23 19:58:06.993417137 +0800
> @@ -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
> @@ -496,6 +497,10 @@ 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;
>
> /*
> @@ -507,6 +512,12 @@ struct mm_struct {
>
> 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
> +
> /* Pointer magic because the dynamic array size confuses some compilers. */
> static inline void mm_init_cpumask(struct mm_struct *mm)
> {
> --- linux.orig/virt/kvm/kvm_main.c 2018-12-23 19:58:06.993417137 +0800
> +++ linux/virt/kvm/kvm_main.c 2018-12-23 19:58:06.993417137 +0800
> @@ -727,6 +727,7 @@ static void kvm_destroy_vm(struct kvm *k
> struct mm_struct *mm = kvm->mm;
>
> kvm_uevent_notify_change(KVM_EVENT_DESTROY_VM, kvm);
> + mm->kvm = NULL;
> kvm_destroy_vm_debugfs(kvm);
> kvm_arch_sync_events(kvm);
> spin_lock(&kvm_lock);
> @@ -3224,6 +3225,8 @@ static int kvm_dev_ioctl_create_vm(unsig
> fput(file);
> return -ENOMEM;
> }
> +
> + kvm->mm->kvm = kvm;
> kvm_uevent_notify_change(KVM_EVENT_CREATE_VM, kvm);
>
> fd_install(r, file);
>
>

Regards,

--
Peter Xu

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