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Message-ID: <20200825101937.GA3252704@myrica>
Date: Tue, 25 Aug 2020 12:19:37 +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>,
Jean-Philippe Brucker <jean-philippe@...aro.com>,
Lu Baolu <baolu.lu@...ux.intel.com>,
Joerg Roedel <joro@...tes.org>,
David Woodhouse <dwmw2@...radead.org>,
Yi Liu <yi.l.liu@...el.com>,
"Tian, Kevin" <kevin.tian@...el.com>,
Raj Ashok <ashok.raj@...el.com>,
Eric Auger <eric.auger@...hat.com>, Wu Hao <hao.wu@...el.com>
Subject: Re: [PATCH v2 4/9] iommu/ioasid: Add reference couting functions
On Fri, Aug 21, 2020 at 09:35:13PM -0700, 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@...ux.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.
> + * No new reference can be added. The IOASID is not returned to the pool
> + * 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.
> + *
> + * - ioasid_find() does not take reference, caller must hold reference
> + *
> + * ioasid_free() can be called multiple times without error until all refs are
> + * dropped.
> + */
Since you already document this in ioasid.rst, I'm not sure the comment
is necessary. Maybe the doc for _free/_put would be better in the
function's documentation.
> +
> +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);
> + /* data found but does not belong to the set */
> + return -EACCES;
> + }
> + refcount_inc(&data->users);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_get_locked);
Is it necessary to export the *_locked variant? Who'd call them and how
would they acquire the lock?
> +
> +/**
> + * ioasid_get - Obtain a reference of an ioasid
> + * @set
> + * @ioasid
Can be dropped. The doc checker will throw a warning, though.
> + *
> + * Check set ownership if @set is non-null.
> + */
> +int ioasid_get(struct ioasid_set *set, ioasid_t ioasid)
> +{
> + int ret = 0;
No need to initialize ret
> +
> + 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);
> + 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);
Please also add the stubs for !CONFIG_IOASID.
Thanks,
Jean
> int ioasid_set_for_each_ioasid(struct ioasid_set *sdata,
> void (*fn)(ioasid_t id, void *data),
> void *data);
> --
> 2.7.4
>
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