iommu/sva: Restore SVA handle sharing

Prior to commit 092edaddb660 ("iommu: Support mm PASID 1:n with sva
domains") the code allowed a SVA handle to be bound multiple times to the
same (mm, device) pair. This was alluded to in the kdoc comment, but we
had understood this to be more a remark about allowing multiple devices,
not a literal same-driver re-opening the same SVA.

It turns out uacce and idxd were both relying on the core code to handle
reference counting for same-device same-mm scenarios. As this looks hard
to resolve in the drivers bring it back to the core code.

The new design has changed the meaning of the domain->users refcount to
refer to the number of devices that are sharing that domain for the same
mm. This is part of the design to lift the SVA domain de-duplication out
of the drivers.

Return the old behavior by explicitly de-duplicating the struct iommu_sva
handle. The same (mm, device) will return the same handle pointer and the
core code will handle tracking this. The last unbind of the handle will
destroy it.

Fixes: 092edaddb660 ("iommu: Support mm PASID 1:n with sva domains")
Reported-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Closes: https://lore.kernel.org/all/20240221110658.529-1-zhangfei.gao@linaro.org/
Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/0-v1-9455fc497a6f+3b4-iommu_sva_sharing_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
index c3fc9201d0be97e59395750cda0fc29940c0b844..7f91c8d0064b71c481395d7febacee8f56567a49 100644 (file)
--- a/drivers/iommu/iommu-sva.c
+++ b/drivers/iommu/iommu-sva.c
@@ -41,6 +41,7 @@ static struct iommu_mm_data *iommu_alloc_mm_data(struct mm_struct *mm, struct de
        }
        iommu_mm->pasid = pasid;
        INIT_LIST_HEAD(&iommu_mm->sva_domains);
+       INIT_LIST_HEAD(&iommu_mm->sva_handles);
        /*
         * Make sure the write to mm->iommu_mm is not reordered in front of
         * initialization to iommu_mm fields. If it does, readers may see a
@@ -82,6 +83,14 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
                goto out_unlock;
        }
 
+       list_for_each_entry(handle, &mm->iommu_mm->sva_handles, handle_item) {
+               if (handle->dev == dev) {
+                       refcount_inc(&handle->users);
+                       mutex_unlock(&iommu_sva_lock);
+                       return handle;
+               }
+       }
+
        handle = kzalloc(sizeof(*handle), GFP_KERNEL);
        if (!handle) {
                ret = -ENOMEM;
@@ -108,7 +117,9 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
        if (ret)
                goto out_free_domain;
        domain->users = 1;
+       refcount_set(&handle->users, 1);
        list_add(&domain->next, &mm->iommu_mm->sva_domains);
+       list_add(&handle->handle_item, &mm->iommu_mm->sva_handles);
 
 out:
        mutex_unlock(&iommu_sva_lock);
@@ -141,6 +152,12 @@ void iommu_sva_unbind_device(struct iommu_sva *handle)
        struct device *dev = handle->dev;
 
        mutex_lock(&iommu_sva_lock);
+       if (!refcount_dec_and_test(&handle->users)) {
+               mutex_unlock(&iommu_sva_lock);
+               return;
+       }
+       list_del(&handle->handle_item);
+
        iommu_detach_device_pasid(domain, dev, iommu_mm->pasid);
        if (--domain->users == 0) {
                list_del(&domain->next);

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 1ea2a820e1eb035c9eea2ec97d9874c52bbd0b42..5e27cb3a3be99b34e705cb7c4569cfbdf2b11f82 100644 (file)
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -892,11 +892,14 @@ struct iommu_fwspec {
 struct iommu_sva {
        struct device                   *dev;
        struct iommu_domain             *domain;
+       struct list_head                handle_item;
+       refcount_t                      users;
 };
 
 struct iommu_mm_data {
        u32                     pasid;
        struct list_head        sva_domains;
+       struct list_head        sva_handles;
 };
 
 int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,