Re: [XEN][PATCH v10 09/20] xen/iommu: Move spin_lock from iommu_dt_device_is_assigned to caller

[Vikram Garhwal <vikram.garhwal@amd.com>]

Hi Michal,
On Tue, Aug 29, 2023 at 10:05:55AM +0200, Michal Orzel wrote:
> 
> 
> On 25/08/2023 10:02, Vikram Garhwal wrote:
> > Rename iommu_dt_device_is_assigned() to iommu_dt_device_is_assigned_locked().
> > 
> > Moving spin_lock to caller was done to prevent the concurrent access to
> > iommu_dt_device_is_assigned while doing add/remove/assign/deassign. Follow-up
> > patches in this series introduces node add/remove feature.
> > 
> > Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
> > 
> > ---
> > Changes from v9:
> >     Make iommu_dt_device_is_assigned_locked() static and delete header.
> >     Move dtdevs_lock before iommu_dt_device_is_assigned_locked().
> > Changes from v7:
> >     Update commit message.
> >     Add ASSERT().
> > ---
> > ---
> >  xen/drivers/passthrough/device_tree.c | 16 ++++++++++++----
> >  1 file changed, 12 insertions(+), 4 deletions(-)
> > 
> > diff --git a/xen/drivers/passthrough/device_tree.c b/xen/drivers/passthrough/device_tree.c
> > index 1c32d7b50c..5d84c07b50 100644
> > --- a/xen/drivers/passthrough/device_tree.c
> > +++ b/xen/drivers/passthrough/device_tree.c
> > @@ -83,16 +83,17 @@ fail:
> >      return rc;
> >  }
> >  
> > -static bool_t iommu_dt_device_is_assigned(const struct dt_device_node *dev)
> > +static bool_t
> > +iommu_dt_device_is_assigned_locked(const struct dt_device_node *dev)
> This does not apply cleanly due to recent change from bool_t to bool. Please rebase for v11 (the function
> should then fit in a single line I think).
Fixed the changes here and made it one-line.
> 
> >  {
> >      bool_t assigned = 0;
> >  
> > +    ASSERT(spin_is_locked(&dtdevs_lock));
> > +
> >      if ( !dt_device_is_protected(dev) )
> >          return 0;
> >  
> > -    spin_lock(&dtdevs_lock);
> >      assigned = !list_empty(&dev->domain_list);
> > -    spin_unlock(&dtdevs_lock);
> >  
> >      return assigned;
> >  }
> > @@ -223,17 +224,24 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct domain *d,
> >          if ( ret )
> >              break;
> >  
> > +        spin_lock(&dtdevs_lock);
> Why is this lock placed here instead of ...
> > +
> >          if ( domctl->cmd == XEN_DOMCTL_test_assign_device )
> >          {
> > -            if ( iommu_dt_device_is_assigned(dev) )
> > +
> ... here, right before iommu_dt_device_is_assigned_locked()?
Moved the lock before iommu_dt_device_is_assigned_locked().
> > +            if ( iommu_dt_device_is_assigned_locked(dev) )
> >              {
> >                  printk(XENLOG_G_ERR "%s already assigned.\n",
> >                         dt_node_full_name(dev));
> >                  ret = -EINVAL;
> >              }
> > +
> > +            spin_unlock(&dtdevs_lock);
> >              break;
> >          }
> >  
> > +        spin_unlock(&dtdevs_lock);
> You could then remove this one.
Ok!
> 
> With the remarks addressed:
> Reviewed-by: Michal Orzel <michal.orzel@amd.com>
> 
> ~Michal