On Thu, Sep 05, 2024 at 10:53:31AM -0700, Nicolin Chen wrote: > On Thu, Sep 05, 2024 at 01:14:15PM -0300, Jason Gunthorpe wrote: > > On Tue, Aug 27, 2024 at 09:59:47AM -0700, Nicolin Chen wrote: > > > Driver can call the iommufd_viommu_find_device() to find a device pointer > > > using its per-viommu virtual ID. The returned device must be protected by > > > the pair of iommufd_viommu_lock/unlock_vdev_id() function. > > > > > > Put these three functions into a new viommu_api file, to build it with the > > > IOMMUFD_DRIVER config. > > > > > > Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx> > > > --- > > > drivers/iommu/iommufd/Makefile | 2 +- > > > drivers/iommu/iommufd/viommu_api.c | 39 ++++++++++++++++++++++++++++++ > > > include/linux/iommufd.h | 16 ++++++++++++ > > > 3 files changed, 56 insertions(+), 1 deletion(-) > > > create mode 100644 drivers/iommu/iommufd/viommu_api.c > > > > I still think this is better to just share the struct content with the > > driver, eventually we want to do this anyhow as the driver will > > want to use container_of() techniques to reach its private data. > > In my mind, exposing everything to the driver is something that > we have to (for driver-managed structures) v.s. we want to... > Even in that case, a driver actually only need to know the size > of the core structure, without touching what's inside(?). > > I am a bit worried that drivers would abuse the content in the > core-level structure.. Providing a set of API would encourage > them to keep the core structure intact, hopefully.. This is always a tension in the kernel. If the core apis can be nice and tidy then it is a reasonable direction But here I think we've cross some threshold where the APIs are complex, want to be inlined and really we just want to expose data not APIs to drivers. > > No need for this lock, xa_load is rcu safe against concurrent writer > > I see iommufd's device.c and main.c grab xa_lock before xa_load? That is not to protect the xa_load, it is to protect the lifetime of pointer it returns Jason
