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From: Auger Eric <eric.auger@redhat.com>
To: Jacob Pan <jacob.pan.linux@gmail.com>,
	iommu@lists.linux-foundation.org,
	LKML <linux-kernel@vger.kernel.org>,
	Jean-Philippe Brucker <jean-philippe@linaro.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	Raj Ashok <ashok.raj@intel.com>, Wu Hao <hao.wu@intel.com>
Subject: Re: [PATCH v2 4/9] iommu/ioasid: Add reference couting functions
Date: Tue, 1 Sep 2020 14:13:00 +0200	[thread overview]
Message-ID: <fed6c93b-8538-662c-2273-19ae2f2f7464@redhat.com> (raw)
In-Reply-To: <1598070918-21321-5-git-send-email-jacob.jun.pan@linux.intel.com>

Hi Jacob,

On 8/22/20 6:35 AM, Jacob Pan wrote:
> There can be multiple users of an IOASID, each user could have hardware
> contexts associated with the IOASID. In order to align lifecycles,
> reference counting is introduced in this patch. It is expected that when
> an IOASID is being freed, each user will drop a reference only after its
> context is cleared.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
>  drivers/iommu/ioasid.c | 113 +++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/ioasid.h |   4 ++
>  2 files changed, 117 insertions(+)
> 
> diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> index f73b3dbfc37a..5f31d63c75b1 100644
> --- a/drivers/iommu/ioasid.c
> +++ b/drivers/iommu/ioasid.c
> @@ -717,6 +717,119 @@ int ioasid_set_for_each_ioasid(struct ioasid_set *set,
>  EXPORT_SYMBOL_GPL(ioasid_set_for_each_ioasid);
>  
>  /**
> + * IOASID refcounting rules
> + * - ioasid_alloc() set initial refcount to 1
> + *
> + * - ioasid_free() decrement and test refcount.
> + *     If refcount is 0, ioasid will be freed. Deleted from the system-wide
> + *     xarray as well as per set xarray. The IOASID will be returned to the
> + *     pool and available for new allocations.
> + *
> + *     If recount is non-zero, mark IOASID as IOASID_STATE_FREE_PENDING.
s/recount/refcount
> + *     No new reference can be added. The IOASID is not returned to the pool
can be taken
> + *     for reuse.
> + *     After free, ioasid_get() will return error but ioasid_find() and other
> + *     non refcount adding APIs will continue to work until the last reference
> + *     is dropped
> + *
> + * - ioasid_get() get a reference on an active IOASID
> + *
> + * - ioasid_put() decrement and test refcount of the IOASID.
> + *     If refcount is 0, ioasid will be freed. Deleted from the system-wide
> + *     xarray as well as per set xarray. The IOASID will be returned to the
> + *     pool and available for new allocations.
> + *     Do nothing if refcount is non-zero.
I would drop this last sentence
> + *
> + * - ioasid_find() does not take reference, caller must hold reference
So can you use ioasid_find() once the state is
IOASID_STATE_FREE_PENDING? According to Jean's reply, the "IOASID may be
freed once ioasid_find() returns but not the returned data." So holding
a ref is not mandated right?
> + *
> + * ioasid_free() can be called multiple times without error until all refs are
> + * dropped.
> + */
> +
> +int ioasid_get_locked(struct ioasid_set *set, ioasid_t ioasid)
> +{
> +	struct ioasid_data *data;
> +
> +	data = xa_load(&active_allocator->xa, ioasid);
> +	if (!data) {
> +		pr_err("Trying to get unknown IOASID %u\n", ioasid);
> +		return -EINVAL;
> +	}
> +	if (data->state == IOASID_STATE_FREE_PENDING) {
> +		pr_err("Trying to get IOASID being freed%u\n", ioasid);
> +		return -EBUSY;
> +	}
> +
> +	if (set && data->set != set) {
> +		pr_err("Trying to get IOASID not in set%u\n", ioasid);
maybe try to normalize your traces using always the same formatting for
ioasids and ioasid sets. Also we can understand %u is the id of the set.
> +		/* data found but does not belong to the set */
you can get rid of this comment
> +		return -EACCES;
> +	}
> +	refcount_inc(&data->users);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_get_locked);
> +
> +/**
> + * ioasid_get - Obtain a reference of an ioasid
> + * @set
> + * @ioasid
> + *
> + * Check set ownership if @set is non-null.
> + */
> +int ioasid_get(struct ioasid_set *set, ioasid_t ioasid)
> +{
> +	int ret = 0;
> +
> +	spin_lock(&ioasid_allocator_lock);
> +	ret = ioasid_get_locked(set, ioasid);
> +	spin_unlock(&ioasid_allocator_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_get);
> +
> +void ioasid_put_locked(struct ioasid_set *set, ioasid_t ioasid)
> +{
> +	struct ioasid_data *data;
> +
> +	data = xa_load(&active_allocator->xa, ioasid);
> +	if (!data) {
> +		pr_err("Trying to put unknown IOASID %u\n", ioasid);
> +		return;
> +	}
> +
> +	if (set && data->set != set) {
> +		pr_err("Trying to drop IOASID not in the set %u\n", ioasid);
was set%u above
> +		return;
> +	}
> +
> +	if (!refcount_dec_and_test(&data->users)) {
> +		pr_debug("%s: IOASID %d has %d remainning users\n",
> +			__func__, ioasid, refcount_read(&data->users));
> +		return;
> +	}
> +	ioasid_do_free(data);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_put_locked);
> +
> +/**
> + * ioasid_put - Drop a reference of an ioasid
> + * @set
> + * @ioasid
> + *
> + * Check set ownership if @set is non-null.
> + */
> +void ioasid_put(struct ioasid_set *set, ioasid_t ioasid)
> +{
> +	spin_lock(&ioasid_allocator_lock);
> +	ioasid_put_locked(set, ioasid);
> +	spin_unlock(&ioasid_allocator_lock);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_put);
> +
> +/**
>   * 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 412d025d440e..310abe4187a3 100644
> --- a/include/linux/ioasid.h
> +++ b/include/linux/ioasid.h
> @@ -76,6 +76,10 @@ int ioasid_attach_data(ioasid_t ioasid, void *data);
>  int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
>  void ioasid_unregister_allocator(struct ioasid_allocator_ops *allocator);
>  void ioasid_is_in_set(struct ioasid_set *set, ioasid_t ioasid);
> +int ioasid_get(struct ioasid_set *set, ioasid_t ioasid);
> +int ioasid_get_locked(struct ioasid_set *set, ioasid_t ioasid);
> +void ioasid_put(struct ioasid_set *set, ioasid_t ioasid);
> +void ioasid_put_locked(struct ioasid_set *set, ioasid_t ioasid);
>  int ioasid_set_for_each_ioasid(struct ioasid_set *sdata,
>  			       void (*fn)(ioasid_t id, void *data),
>  			       void *data);
> 
Thanks

Eric

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  parent reply	other threads:[~2020-09-01 12:13 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-22  4:35 [PATCH v2 0/9] IOASID extensions for guest SVA Jacob Pan
2020-08-22  4:35 ` [PATCH v2 1/9] docs: Document IO Address Space ID (IOASID) APIs Jacob Pan
2020-08-23  7:05   ` Lu Baolu
2020-08-28 17:01     ` Jacob Pan
2020-08-24 10:32   ` Jean-Philippe Brucker
2020-08-27 16:21     ` Auger Eric
2020-09-01 16:56       ` Jacob Pan
2020-09-07  8:03         ` Auger Eric
2020-09-08 17:29           ` Jacob Pan
2020-08-28 22:24     ` Jacob Pan
2020-08-22  4:35 ` [PATCH v2 2/9] iommu/ioasid: Rename ioasid_set_data() Jacob Pan
2020-08-24 18:29   ` Jean-Philippe Brucker
2020-09-01 11:51   ` Auger Eric
2020-08-22  4:35 ` [PATCH v2 3/9] iommu/ioasid: Introduce ioasid_set APIs Jacob Pan
2020-08-22 12:53   ` kernel test robot
2020-08-24  2:24   ` Lu Baolu
2020-09-01 21:28     ` Jacob Pan
2020-09-02  2:39       ` Lu Baolu
2020-08-24 18:28   ` Jean-Philippe Brucker
2020-08-24 18:30     ` Randy Dunlap
2020-09-02 21:46       ` Jacob Pan
2020-08-24 18:34     ` Randy Dunlap
2020-09-02 21:47       ` Jacob Pan
2020-09-02 21:44     ` Jacob Pan
2020-09-01 11:51   ` Auger Eric
2020-09-03 21:07     ` Jacob Pan
2020-09-07  8:04       ` Auger Eric
2020-08-22  4:35 ` [PATCH v2 4/9] iommu/ioasid: Add reference couting functions Jacob Pan
2020-08-24  2:26   ` Lu Baolu
2020-08-25 10:20     ` Jean-Philippe Brucker
2020-08-25 10:19   ` Jean-Philippe Brucker
2020-09-08 20:30     ` Jacob Pan
2020-09-01 12:13   ` Auger Eric [this message]
2020-09-08 20:49     ` Jacob Pan
2020-09-24 18:29   ` Shameerali Kolothum Thodi
2020-08-22  4:35 ` [PATCH v2 5/9] iommu/ioasid: Introduce ioasid_set private ID Jacob Pan
2020-08-22  8:36   ` kernel test robot
2020-08-22  9:03   ` kernel test robot
2020-08-25 10:22   ` Jean-Philippe Brucker
2020-09-08 22:19     ` Jacob Pan
2020-09-01 15:38   ` Auger Eric
2020-09-08 22:40     ` Jacob Pan
2020-09-10  9:18       ` Auger Eric
2020-08-22  4:35 ` [PATCH v2 6/9] iommu/ioasid: Introduce notification APIs Jacob Pan
2020-08-25 10:26   ` Jean-Philippe Brucker
2020-09-09 20:37     ` Jacob Pan
2020-09-01 16:49   ` Auger Eric
2020-09-09 22:58     ` Jacob Pan
2020-09-10  8:59       ` Auger Eric
2020-08-22  4:35 ` [PATCH v2 7/9] iommu/vt-d: Listen to IOASID notifications Jacob Pan
2020-09-01 17:03   ` Auger Eric
2020-09-10  4:54     ` Jacob Pan
2020-08-22  4:35 ` [PATCH v2 8/9] iommu/vt-d: Send IOASID bind/unbind notifications Jacob Pan
2020-08-22  4:35 ` [PATCH v2 9/9] iommu/vt-d: Store guest PASID during bind Jacob Pan
2020-09-01 17:08   ` Auger Eric
2020-09-10 17:12     ` Jacob Pan

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