linux-kernel - Re: [PATCH v2 3/6] iommu: Same critical region for device release and removal

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Date:   Sat, 18 Feb 2023 15:29:12 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/6] iommu: Same critical region for device release and
 removal

On 2/17/23 11:40 PM, Jason Gunthorpe wrote:
> On Fri, Feb 17, 2023 at 05:47:33PM +0800, Lu Baolu wrote:
>> In a non-driver context, it is crucial to ensure the consistency of a
>> device's iommu ops. Otherwise, it may result in a situation where a
>> device is released but it's iommu ops are still used.
>>
>> Put the ops->release_device and __iommu_group_remove_device() in a some
>> group->mutext critical region, so that, as long as group->mutex is held
>> and the device is in its group's device list, its iommu ops are always
>> consistent.
>>
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/iommu.c | 15 +++++++++++++--
>>   1 file changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 6247883991e2..093692308b80 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -101,6 +101,10 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
>>   static struct iommu_group *iommu_group_get_for_dev(struct device *dev);
>>   static ssize_t iommu_group_store_type(struct iommu_group *group,
>>   				      const char *buf, size_t count);
>> +static struct group_device *
>> +__iommu_group_remove_device(struct iommu_group *group, struct device *dev);
>> +static void __iommu_group_release_device(struct iommu_group *group,
>> +					 struct group_device *grp_dev);
> Seems like a hunk is missing from this patch?

Did you mean below block of change? If so, I will add it in the next
version.

+
+	/*
+	 * If the group has become empty then ownership must have been released,
+	 * and the current domain must be set back to NULL or the default
+	 * domain.
+	 */
+	if (list_empty(&group->devices))
+		WARN_ON(group->owner_cnt ||
+			group->domain != group->default_domain);
+
+	/*
+	 * release_device() must stop using any attached domain on the device.
+	 * If there are still other devices in the group they are not effected
+	 * by this callback.
+	 *
+	 * The IOMMU driver must set the device to either an identity or
+	 * blocking translation and stop using any domain pointer, as it is
+	 * going to be freed.
+	 */
  	if (ops->release_device)
  		ops->release_device(dev);
+	mutex_unlock(&group->mutex);

By the way, can I add you signed-off-by when I use the code you posted
in the discussion thread?

Best regards,
baolu