Re: [PATCH v3 06/14] iommu/ioasid: Introduce API to adjust the quota of an ioasid_set

Jean-Philippe Brucker
2020-10-21T14:57:36Z

On Mon, Sep 28, 2020 at 02:38:33PM -0700, Jacob Pan wrote:
> Each ioasid_set is given a quota during allocation. As system
> administrators balance resources among VMs, we shall support the
> adjustment of quota at runtime. The new quota cannot be less than the
> outstanding IOASIDs already allocated within the set. The extra quota
> will be returned to the system-wide IOASID pool if the new quota is
> smaller than the existing one.
>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>

Minor comments below, but

Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

> ---
> drivers/iommu/ioasid.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/ioasid.h | 6 ++++++
> 2 files changed, 53 insertions(+)
>
> diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> index 61e25c2375ab..cf8c7d34e2de 100644
> --- a/drivers/iommu/ioasid.c
> +++ b/drivers/iommu/ioasid.c
> @@ -654,6 +654,53 @@ void ioasid_set_put(struct ioasid_set *set)
> EXPORT_SYMBOL_GPL(ioasid_set_put);
>
> /**
> + * ioasid_adjust_set - Adjust the quota of an IOASID set
> + * @set: IOASID set to be assigned
> + * @quota: Quota allowed in this set
> + *
> + * Return 0 on success. If the new quota is smaller than the number of
> + * IOASIDs already allocated, -EINVAL will be returned. No change will be
> + * made to the existing quota.
> + */
> +int ioasid_adjust_set(struct ioasid_set *set, int quota)

@quota probably doesn't need to be signed (since it's the same as an
ioasid_t, which is unsigned).

> +{
> + int ret = 0;
> +
> + if (quota <= 0)
> + return -EINVAL;
> +
> + spin_lock(&ioasid_allocator_lock);
> + if (set->nr_ioasids > quota) {
> + pr_err("New quota %d is smaller than outstanding IOASIDs %d\n",
> + quota, set->nr_ioasids);
> + ret = -EINVAL;
> + goto done_unlock;
> + }
> +
> + if ((quota > set->quota) &&
> + (quota - set->quota > ioasid_capacity_avail)) {

misaligned

> + ret = -ENOSPC;
> + goto done_unlock;
> + }
> +
> + /* Return the delta back to system pool */
> + ioasid_capacity_avail += set->quota - quota;
> +
> + /*
> + * May have a policy to prevent giving all available IOASIDs
> + * to one set. But we don't enforce here, it should be in the
> + * upper layers.
> + */

I think here would be OK to check about fairness. But anyway, we don't
have to worry about this yet, so I'd just drop the comment.

Thanks,
Jean

> + set->quota = quota;
> +
> +done_unlock:
> + spin_unlock(&ioasid_allocator_lock);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_adjust_set);
> +
> +/**
> * ioasid_find - Find IOASID data
> * @set: the IOASID set
> * @ioasid: the IOASID to find
> diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
> index 1ae213b660f0..0a5e82148eb9 100644
> --- a/include/linux/ioasid.h
> +++ b/include/linux/ioasid.h
> @@ -62,6 +62,7 @@ struct ioasid_allocator_ops {
> void ioasid_install_capacity(ioasid_t total);
> ioasid_t ioasid_get_capacity(void);
> struct ioasid_set *ioasid_set_alloc(void *token, ioasid_t quota, int type);
> +int ioasid_adjust_set(struct ioasid_set *set, int quota);
> void ioasid_set_get(struct ioasid_set *set);
> void ioasid_set_put(struct ioasid_set *set);
>
> @@ -99,6 +100,11 @@ static inline struct ioasid_set *ioasid_set_alloc(void *token, ioasid_t quota, i
> return ERR_PTR(-ENOTSUPP);
> }
>
> +static inline int ioasid_adjust_set(struct ioasid_set *set, int quota)
> +{
> + return -ENOTSUPP;
> +}
> +
> static inline void ioasid_set_put(struct ioasid_set *set)
> {
> }
> --
> 2.7.4
>