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SubjectRe: [PATCH 2/4] iommu: Use group ownership to avoid driver attachment
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On 2/15/23 8:56 PM, Jason Gunthorpe wrote:
> On Wed, Feb 15, 2023 at 01:51:14PM +0800, Baolu Lu wrote:
>> On 2/13/23 10:19 PM, Jason Gunthorpe wrote:
>>> On Mon, Feb 13, 2023 at 03:49:39PM +0800, Lu Baolu wrote:
>>>> The iommu_group_store_type() requires the devices in the iommu group are
>>>> not bound to any device driver during the whole operation. The existing
>>>> code locks the device with device_lock(dev) and use device_is_bound() to
>>>> check whether any driver is bound to device.
>>>>
>>>> In fact, this can be achieved through the DMA ownership helpers. Replace
>>>> them with iommu_group_claim/release_dma_owner() helpers.
>>>>
>>>> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>
>>>> ---
>>>> drivers/iommu/iommu.c | 27 +++++++++++++--------------
>>>> 1 file changed, 13 insertions(+), 14 deletions(-)
>>>>
>>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>>> index 4f71dcd2621b..6547cb38480c 100644
>>>> --- a/drivers/iommu/iommu.c
>>>> +++ b/drivers/iommu/iommu.c
>>>> @@ -2807,12 +2807,6 @@ static int iommu_change_dev_def_domain(struct iommu_group *group,
>>>> mutex_lock(&group->mutex);
>>>> - if (group->default_domain != group->domain) {
>>>> - dev_err_ratelimited(prev_dev, "Group not assigned to default domain\n");
>>>> - ret = -EBUSY;
>>>> - goto out;
>>>> - }
>>>> -
>>>> /*
>>>> * iommu group wasn't locked while acquiring device lock in
>>>> * iommu_group_store_type(). So, make sure that the device count hasn't
>>>> @@ -2971,6 +2965,7 @@ static void iommu_group_unfreeze_dev_ops(struct iommu_group *group)
>>>> static ssize_t iommu_group_store_type(struct iommu_group *group,
>>>> const char *buf, size_t count)
>>>> {
>>>> + bool group_owner_claimed = false;
>>>> struct group_device *grp_dev;
>>>> struct device *dev;
>>>> int ret, req_type;
>>>> @@ -2992,6 +2987,14 @@ static ssize_t iommu_group_store_type(struct iommu_group *group,
>>>> else
>>>> return -EINVAL;
>>>> + if (req_type != IOMMU_DOMAIN_DMA_FQ ||
>>>> + group->default_domain->type != IOMMU_DOMAIN_DMA) {
>>>> + ret = iommu_group_claim_dma_owner(group, (void *)buf);
>>>> + if (ret)
>>>> + return ret;
>>>> + group_owner_claimed = true;
>>>> + }
>>> I don't get it, this should be done unconditionally. If we couldn't
>>> take ownership then we simply can't progress.
>> The existing code allows the user to switch the default domain from
>> strict to lazy invalidation mode. The default domain is not changed,
>> hence it should be seamless and transparent to the device driver.
> So make that a special case, get the group lock check if it is this
> case and then just adjust it and exit, otherwise get ownership under
> the group lock as discussed.

OK. Will do like this in the next version.

Best regards,
baolu

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