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The ice driver stores VF structures in a simple array which is allocated once at the time of VF creation. The VF structures are then accessed from the array by their VF ID. The ID must be between 0 and the number of allocated VFs. Multiple threads can access this table: * .ndo operations such as .ndo_get_vf_cfg or .ndo_set_vf_trust * interrupts, such as due to messages from the VF using the virtchnl communication * processing such as device reset * commands to add or remove VFs The current implementation does not keep track of when all threads are done operating on a VF and can potentially result in use-after-free issues caused by one thread accessing a VF structure after it has been released when removing VFs. Some of these are prevented with various state flags and checks. In addition, this structure is quite static and does not support a planned future where virtualization can be more dynamic. As we begin to look at supporting Scalable IOV with the ice driver (as opposed to just supporting Single Root IOV), this structure is not sufficient. In the future, VFs will be able to be added and removed individually and dynamically. To allow for this, and to better protect against a whole class of use-after-free bugs, replace the VF storage with a combination of a hash table and krefs to reference track all of the accesses to VFs through the hash table. A hash table still allows efficient look up of the VF given its ID, but also allows adding and removing VFs. It does not require contiguous VF IDs. The use of krefs allows the cleanup of the VF memory to be delayed until after all threads have released their reference (by calling ice_put_vf). To prevent corruption of the hash table, a combination of RCU and the mutex table_lock are used. Addition and removal from the hash table use the RCU-aware hash macros. This allows simple read-only look ups that iterate to locate a single VF can be fast using RCU. Accesses which modify the hash table, or which can't take RCU because they sleep, will hold the mutex lock. By using this design, we have a stronger guarantee that the VF structure can't be released until after all threads are finished operating on it. We also pave the way for the more dynamic Scalable IOV implementation in the future. Signed-off-by: Jacob Keller <jacob.e.keller@intel.com> Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com> Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com> |
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
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| usr | ||
| virt | ||
| .clang-format | ||
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.