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

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Date:   Wed, 21 Oct 2020 16:57:09 +0200
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jacob Pan <jacob.pan.linux@...il.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Jonathan Corbet <corbet@....net>, linux-api@...r.kernel.org,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>, Wu Hao <hao.wu@...el.com>,
        Yi Sun <yi.y.sun@...el.com>, Dave Jiang <dave.jiang@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v3 06/14] iommu/ioasid: Introduce API to adjust the quota
 of an ioasid_set

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@...ux.intel.com>

Minor comments below, but

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