[RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

[Alex Williamson]

On Tue,  2 Oct 2018 13:22:31 +1000
Alexey Kardashevskiy <aik at ozlabs.ru> wrote:

> As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
> memory. If there is a bug in memory release, the loop in
> tce_iommu_release() becomes infinite; this actually happened to me.
> 
> This makes the loop finite and prints a warning on every failure to make
> the code more bug prone.
> 
> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
> ---
>  drivers/vfio/vfio_iommu_spapr_tce.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)

Should this have a stable/fixes tag?  Looks like it's relevant to:

4b6fad7097f8 powerpc/mm/iommu, vfio/spapr: Put pages on VFIO container shutdown

Also, not sure who you're wanting to take this since it was sent to ppc
lists.  If it's me, let me know, otherwise

Acked-by: Alex Williamson <alex.williamson at redhat.com>

Thanks,
Alex

> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index b1a8ab3..ece0651 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -371,6 +371,7 @@ static void tce_iommu_release(void *iommu_data)
>  {
>  	struct tce_container *container = iommu_data;
>  	struct tce_iommu_group *tcegrp;
> +	struct tce_iommu_prereg *tcemem, *tmtmp;
>  	long i;
>  
>  	while (tce_groups_attached(container)) {
> @@ -393,13 +394,8 @@ static void tce_iommu_release(void *iommu_data)
>  		tce_iommu_free_table(container, tbl);
>  	}
>  
> -	while (!list_empty(&container->prereg_list)) {
> -		struct tce_iommu_prereg *tcemem;
> -
> -		tcemem = list_first_entry(&container->prereg_list,
> -				struct tce_iommu_prereg, next);
> -		WARN_ON_ONCE(tce_iommu_prereg_free(container, tcemem));
> -	}
> +	list_for_each_entry_safe(tcemem, tmtmp, &container->prereg_list, next)
> +		WARN_ON(tce_iommu_prereg_free(container, tcemem));
>  
>  	tce_iommu_disable(container);
>  	if (container->mm)