linux-kernel - Re: [PATCH v2 8/8] vdpa_sim: add support for user VA

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Message-ID: <20230316091142.p2ogqf3q2fsyha3l@sgarzare-redhat>
Date:   Thu, 16 Mar 2023 10:11:42 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        Andrey Zhadchenko <andrey.zhadchenko@...tuozzo.com>,
        eperezma@...hat.com, netdev@...r.kernel.org, stefanha@...hat.com,
        linux-kernel@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH v2 8/8] vdpa_sim: add support for user VA

On Tue, Mar 14, 2023 at 01:36:13PM +0800, Jason Wang wrote:
>On Thu, Mar 2, 2023 at 7:35 PM Stefano Garzarella <sgarzare@...hat.com> wrote:
>>
>> The new "use_va" module parameter (default: false) is used in
>> vdpa_alloc_device() to inform the vDPA framework that the device
>> supports VA.
>>
>> vringh is initialized to use VA only when "use_va" is true and the
>> user's mm has been bound. So, only when the bus supports user VA
>> (e.g. vhost-vdpa).
>>
>> vdpasim_mm_work_fn work is used to attach the kthread to the user
>> address space when the .bind_mm callback is invoked, and to detach
>> it when the .unbind_mm callback is invoked.
>>
>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>> ---
>>
>> Notes:
>>     v2:
>>     - `use_va` set to true by default [Eugenio]
>>     - supported the new unbind_mm callback [Jason]
>>     - removed the unbind_mm call in vdpasim_do_reset() [Jason]
>>     - avoided to release the lock while call kthread_flush_work() since we
>>       are now using a mutex to protect the device state
>>
>>  drivers/vdpa/vdpa_sim/vdpa_sim.h |  1 +
>>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 98 +++++++++++++++++++++++++++++++-
>>  2 files changed, 97 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> index 4774292fba8c..3a42887d05d9 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> @@ -59,6 +59,7 @@ struct vdpasim {
>>         struct vdpasim_virtqueue *vqs;
>>         struct kthread_worker *worker;
>>         struct kthread_work work;
>> +       struct mm_struct *mm_bound;
>>         struct vdpasim_dev_attr dev_attr;
>>         /* mutex to synchronize virtqueue state */
>>         struct mutex mutex;
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> index a28103a67ae7..eda26bc33df5 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> @@ -35,10 +35,77 @@ module_param(max_iotlb_entries, int, 0444);
>>  MODULE_PARM_DESC(max_iotlb_entries,
>>                  "Maximum number of iotlb entries for each address space. 0 means unlimited. (default: 2048)");
>>
>> +static bool use_va = true;
>> +module_param(use_va, bool, 0444);
>> +MODULE_PARM_DESC(use_va, "Enable/disable the device's ability to use VA");
>> +
>>  #define VDPASIM_QUEUE_ALIGN PAGE_SIZE
>>  #define VDPASIM_QUEUE_MAX 256
>>  #define VDPASIM_VENDOR_ID 0
>>
>> +struct vdpasim_mm_work {
>> +       struct kthread_work work;
>> +       struct mm_struct *mm;
>> +       bool bind;
>> +       int ret;
>> +};
>> +
>> +static void vdpasim_mm_work_fn(struct kthread_work *work)
>> +{
>> +       struct vdpasim_mm_work *mm_work =
>> +               container_of(work, struct vdpasim_mm_work, work);
>> +
>> +       mm_work->ret = 0;
>> +
>> +       if (mm_work->bind) {
>> +               kthread_use_mm(mm_work->mm);
>> +               //TODO: should we attach the cgroup of the mm owner?
>> +       } else {
>> +               kthread_unuse_mm(mm_work->mm);
>> +       }
>> +}
>> +
>> +static void vdpasim_worker_queue_mm(struct vdpasim *vdpasim,
>> +                                   struct vdpasim_mm_work *mm_work)
>> +{
>
>Nit: we need to tweak the name as it does flush besides queuing the work.

Yep, or split in 2 functions.

>
>> +       struct kthread_work *work = &mm_work->work;
>> +
>> +       kthread_init_work(work, vdpasim_mm_work_fn);
>> +       kthread_queue_work(vdpasim->worker, work);
>> +
>> +       kthread_flush_work(work);
>> +}
>> +
>> +static int vdpasim_worker_bind_mm(struct vdpasim *vdpasim,
>> +                                 struct mm_struct *new_mm)
>> +{
>> +       struct vdpasim_mm_work mm_work;
>> +
>> +       mm_work.mm = new_mm;
>> +       mm_work.bind = true;
>> +
>> +       vdpasim_worker_queue_mm(vdpasim, &mm_work);
>> +
>> +       if (!mm_work.ret)
>> +               vdpasim->mm_bound = new_mm;
>> +
>> +       return mm_work.ret;
>> +}
>> +
>> +static void vdpasim_worker_unbind_mm(struct vdpasim *vdpasim)
>> +{
>> +       struct vdpasim_mm_work mm_work;
>> +
>> +       if (!vdpasim->mm_bound)
>> +               return;
>> +
>> +       mm_work.mm = vdpasim->mm_bound;
>> +       mm_work.bind = false;
>
>Can we simply use mm_work.mm = NULL for unbinding?
>
>> +
>> +       vdpasim_worker_queue_mm(vdpasim, &mm_work);
>> +
>> +       vdpasim->mm_bound = NULL;
>
>And change the mm_bound in the worker?

Yep, I need to put `vdpasim` in struct vdpasim_mm_work.

I'll do in the next version.

Thanks,
Stefano