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commitf058599e22upstream. The s390_mmio_read/write syscalls are currently broken when running with MIO. The new pcistb_mio/pcstg_mio/pcilg_mio instructions are executed similiarly to normal load/store instructions and do address translation in the current address space. That means inside the kernel they are aware of mappings into kernel address space while outside the kernel they use user space mappings (usually created through mmap'ing a PCI device file). Now when existing user space applications use the s390_pci_mmio_write and s390_pci_mmio_read syscalls, they pass I/O addresses that are mapped into user space so as to be usable with the new instructions without needing a syscall. Accessing these addresses with the old instructions as done currently leads to a kernel panic. Also, for such a user space mapping there may not exist an equivalent kernel space mapping which means we can't just use the new instructions in kernel space. Instead of replicating user mappings in the kernel which then might collide with other mappings, we can conceptually execute the new instructions as if executed by the user space application using the secondary address space. This even allows us to directly store to the user pointer without the need for copy_to/from_user(). Cc: stable@vger.kernel.org Fixes:71ba41c9b1("s390/pci: provide support for MIO instructions") Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com> Reviewed-by: Sven Schnelle <svens@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.