Messages in this thread | | | Date | Wed, 15 Feb 2023 08:56:33 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH 2/4] iommu: Use group ownership to avoid driver attachment |
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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. > > > which also means this needs to be > > an externally version of iommu_group_claim_dma_owner() > > Sorry! What does "an externally version of > iommu_group_claim_dma_owner()" mean? >
Oops "externally locked"
> My understanding is that we should limit iommu_group_claim_dma_owner() > use in the driver context. For this non-driver context, we should not > use iommu_group_claim_dma_owner() directly, but hold the group->mutex > and check the group->owner_cnt directly: > > mutex_lock(&group->mutex); > if (group->owner_cnt) { > ret = -EPERM; > goto unlock_out; > } > > the group->mutex should be held until everything is done.
Yes, that would be fine as long as we can hold the group mutex throughout
Jason
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