Re: [PATCH rc] iommu/sva: Restore SVA handle sharing

[Zhangfei Gao <zhangfei.gao@linaro.org>]

On Thu, 22 Feb 2024 at 22:07, Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> 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>

Thanks Jason