Re: [PATCH v11 12/16] iommu: Use refcount for fault data access

[Baolu Lu]

On 2024/2/5 16:37, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, January 30, 2024 4:09 PM
> >
> > The per-device fault data structure stores information about faults
> > occurring on a device. Its lifetime spans from IOPF enablement to
> > disablement. Multiple paths, including IOPF reporting, handling, and
> > responding, may access it concurrently.
> >
> > Previously, a mutex protected the fault data from use after free. But
> > this is not performance friendly due to the critical nature of IOPF
> > handling paths.
> >
> > Refine this with a refcount-based approach. The fault data pointer is
> > obtained within an RCU read region with a refcount. The fault data
> > pointer is returned for usage only when the pointer is valid and a
> > refcount is successfully obtained. The fault data is freed with
> > kfree_rcu(), ensuring data is only freed after all RCU critical regions
> > complete.
> >
> > An iopf handling work starts once an iopf group is created. The handling
> > work continues until iommu_page_response() is called to respond to the
> > iopf and the iopf group is freed. During this time, the device fault
> > parameter should always be available. Add a pointer to the device fault
> > parameter in the iopf_group structure and hold the reference until the
> > iopf_group is freed.
> >
> > Make iommu_page_response() static as it is only used in io-pgfault.c.
> >
> > Co-developed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Tested-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
>
> >    * struct iommu_fault_param - per-device IOMMU fault data
> >    * @lock: protect pending faults list
> > + * @users: user counter to manage the lifetime of the data
> > + * @ruc: rcu head for kfree_rcu()
>
> s/ruc/rcu

Fixed. Thank you!

Best regards,
baolu