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Tue, 25 Aug 2020 03:19:54 -0700 (PDT) Date: Tue, 25 Aug 2020 12:19:37 +0200 From: Jean-Philippe Brucker To: Jacob Pan Subject: Re: [PATCH v2 4/9] iommu/ioasid: Add reference couting functions Message-ID: <20200825101937.GA3252704@myrica> References: <1598070918-21321-1-git-send-email-jacob.jun.pan@linux.intel.com> <1598070918-21321-5-git-send-email-jacob.jun.pan@linux.intel.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1598070918-21321-5-git-send-email-jacob.jun.pan@linux.intel.com> Cc: "Tian, Kevin" , Raj Ashok , Jean-Philippe Brucker , LKML , iommu@lists.linux-foundation.org, Wu Hao , David Woodhouse X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" 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 > --- > 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 > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu