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Message-ID: <CACLfguXH7oEgjaOYWC05742n0dsUGaFWM-i7Fykuzbxv9xQ9HA@mail.gmail.com>
Date: Thu, 7 Nov 2024 19:50:12 +0800
From: Cindy Lu <lulu@...hat.com>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: jasowang@...hat.com, mst@...hat.com, michael.christie@...cle.com,
linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org
Subject: Re: [PATCH v3 7/9] vhost: Add new UAPI to support change to task mode
On Thu, Nov 7, 2024 at 6:03 PM Stefano Garzarella <sgarzare@...hat.com> wrote:
>
> On Thu, Nov 07, 2024 at 03:12:49PM +0800, Cindy Lu wrote:
> >On Tue, Nov 5, 2024 at 6:32 PM Stefano Garzarella <sgarzare@...hat.com> wrote:
> >>
> >> On Tue, Nov 05, 2024 at 03:25:26PM +0800, Cindy Lu wrote:
> >> >Add a new UAPI to enable setting the vhost device to task mode.
> >> >The userspace application can use VHOST_SET_INHERIT_FROM_OWNER
> >> >to configure the mode if necessary.
> >> >This setting must be applied before VHOST_SET_OWNER, as the worker
> >> >will be created in the VHOST_SET_OWNER function
> >> >
> >> >Signed-off-by: Cindy Lu <lulu@...hat.com>
> >> >---
> >> > drivers/vhost/vhost.c | 15 ++++++++++++++-
> >> > include/uapi/linux/vhost.h | 2 ++
> >> > 2 files changed, 16 insertions(+), 1 deletion(-)
> >> >
> >> >diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >> >index c17dc01febcc..70c793b63905 100644
> >> >--- a/drivers/vhost/vhost.c
> >> >+++ b/drivers/vhost/vhost.c
> >> >@@ -2274,8 +2274,9 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> >> > {
> >> > struct eventfd_ctx *ctx;
> >> > u64 p;
> >> >- long r;
> >> >+ long r = 0;
> >>
> >> I don't know if something is missing in this patch, but I am confused:
> >>
> >> `r` is set few lines below...
> >>
> >> > int i, fd;
> >> >+ bool inherit_owner;
> >> >
> >> > /* If you are not the owner, you can become one */
> >> > if (ioctl == VHOST_SET_OWNER) {
> >> ...
> >>
> >> /* You must be the owner to do anything else */
> >> r = vhost_dev_check_owner(d);
> >> if (r)
> >> goto done;
> >>
> >> So, why we are now initializing it to 0?
> >>
> >r = 0 mean return successfully here.
> >Therefore, in the case VHOST_SET_INHERIT_FROM_OWNER function, I don't
> >need to set it again and can simply return.
> >....
> > if (vhost_dev_has_owner(d))
> > break;
> >.....
>
> Okay, but vhost_dev_check_owner() already set it to 0, so we can avoid
> that, no?
>
> >> >@@ -2332,6 +2333,18 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> >> > if (ctx)
> >> > eventfd_ctx_put(ctx);
> >> > break;
> >> >+ case VHOST_SET_INHERIT_FROM_OWNER:
> >> >+ /*inherit_owner can only be modified before owner is set*/
> >> >+ if (vhost_dev_has_owner(d))
> >>
> >> And here, how this check can be false, if at the beginning of the
> >> function we call vhost_dev_check_owner()?
> >>
> >> Maybe your intention was to add this code before the
> >> `vhost_dev_check_owner()` call, so this should explain why initialize
> >> `r` to 0, but I'm not sure.
> >>
> >Yes, in the function beginning, the code is
> >if (ioctl == VHOST_SET_OWNER) {
> >r = vhost_dev_set_owner(d);
> >goto done;
> >}
> >if the ioctl is not VHOST_SET_OWNER, then the code will not run the
> >function vhost_dev_set_owner.
>
> Sorry, I meant vhost_dev_check_owner(), not vhost_dev_set_owner().
>
> I'll try to explain again.
>
> After applying this series we have this code:
>
> long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> {
> struct eventfd_ctx *ctx;
> u64 p;
> long r = 0;
> int i, fd;
> bool inherit_owner;
>
> /* If you are not the owner, you can become one */
> if (ioctl == VHOST_SET_OWNER) {
> r = vhost_dev_set_owner(d);
> goto done;
> }
>
> /* You must be the owner to do anything else */
> r = vhost_dev_check_owner(d);
> if (r)
> goto done;
>
> switch (ioctl) {
> ...
> case VHOST_SET_INHERIT_FROM_OWNER:
> /*inherit_owner can only be modified before owner is
> * set*/
> if (vhost_dev_has_owner(d))
> break;
>
> IIUC this check is always true, so we always call `break` because at
> the beginning of this function we call vhost_dev_check_owner() which
> if `dev->mm != current->mm` (so it can't be null I guess) jumps directly
> into `done`, returning an error.
>
> So I still don't understand in which condition we can run the code after
> this check.
>
oh sorry I missed that check. I will move the new case back to the top
of function,
I didn't think it through before making this change; I just wanted to
clean up the code but forgot about the status.
Thanks
cindy
> Thanks,
> Stefano
>
> if (copy_from_user(&inherit_owner, argp,
> sizeof(inherit_owner))) {
> r = -EFAULT;
> break;
> }
> d->inherit_owner = inherit_owner;
> break;
>
>
> >This ioctl is used by userspace applications, so we cannot be certain
> >of the type and sequence of their calls; therefore, I added this
> >check.
> >
> >> >+ break;
> >>
> >> Should we return an error (e.g. -EPERM) in this case?
> >>
> >sure，will add this back
> >thanks
> >Cindy
> >> >+
> >> >+ if (copy_from_user(&inherit_owner, argp,
> >> >+ sizeof(inherit_owner))) {
> >> >+ r = -EFAULT;
> >> >+ break;
> >> >+ }
> >> >+ d->inherit_owner = inherit_owner;
> >> >+ break;
> >> > default:
> >> > r = -ENOIOCTLCMD;
> >> > break;
> >> >diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> >> >index b95dd84eef2d..1e192038633d 100644
> >> >--- a/include/uapi/linux/vhost.h
> >> >+++ b/include/uapi/linux/vhost.h
> >> >@@ -235,4 +235,6 @@
> >> > */
> >> > #define VHOST_VDPA_GET_VRING_SIZE _IOWR(VHOST_VIRTIO, 0x82, \
> >> > struct vhost_vring_state)
> >> >+
> >>
> >> Please add a documentation here, this is UAPI, so the user should
> >> know what this ioctl does based on the parameter.
> >>
> >> Thanks,
> >> Stefano
> >>
> >> >+#define VHOST_SET_INHERIT_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, bool)
> >> > #endif
> >> >--
> >> >2.45.0
> >> >
> >>
> >
>
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