Re: [XEN][RFC PATCH v3 07/14] xen/iommu: Move spin_lock from iommu_dt_device_is_assigned to caller

[Julien Grall <julien@xxxxxxx>]

Hi,

On 08/03/2022 19:46, Vikram Garhwal wrote:
> Rename iommu_dt_device_is_assigned() to iommu_dt_device_is_assigned_lock().
>
> Moving spin_lock to caller was done to prevent the concurrent access to
> iommu_dt_device_is_assigned while doing add/remove/assign/deassign.
>
> Signed-off-by: Vikram Garhwal <fnu.vikram@xxxxxxxxxx>
> ---
>   xen/drivers/passthrough/device_tree.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/xen/drivers/passthrough/device_tree.c 
> b/xen/drivers/passthrough/device_tree.c
> index 98f2aa0dad..b3b04f8e03 100644
> --- a/xen/drivers/passthrough/device_tree.c
> +++ b/xen/drivers/passthrough/device_tree.c
> @@ -83,16 +83,14 @@ 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_lock(const struct dt_device_node 
> *dev)
NIT: We tend to use "_locked" when a function should be called with the 
lock taken.
>   {
>       bool_t assigned = 0;
>   
>       if ( !dt_device_is_protected(dev) )
>           return 0;
>   
> -    spin_lock(&dtdevs_lock);
>       assigned = !list_empty(&dev->domain_list);
> -    spin_unlock(&dtdevs_lock);
>   
>       return assigned;
>   }
> @@ -225,12 +223,17 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct 
> domain *d,
>   
>           if ( domctl->cmd == XEN_DOMCTL_test_assign_device )
>           {
> -            if ( iommu_dt_device_is_assigned(dev) )
> +            spin_lock(&dtdevs_lock);
Is this actually sufficient? IOW what will ensure that the "dev" doesn't 
disappear between the time we look it up (see dt_find_node_by_gpath()) 
and we check the assignment?
Cheers,

--
Julien Grall