Re: [PATCH 2/4] iommu: Use group ownership to avoid driver attachment

[Baolu Lu]

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@xxxxxxxxxxxxxxx>
> > > > ---
> > > >    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