70be49f2f6
Commit df24e1783e6e ("parisc: Add vDSO support") introduced the vDSO
support, for which a _PAGE_SPECIAL page table flag was needed. Since we
wanted to keep every page table entry in 32-bits, this patch re-used the
existing - but yet unused - _PAGE_DMB flag (which triggers a hardware break
if a page is accessed) to store the special bit.
But when graphics card memory is mmapped into userspace, the kernel uses
vm_iomap_memory() which sets the the special flag. So, with the DMB bit
set, every access to the graphics memory now triggered a hardware
exception and segfaulted the userspace program.
Fix this breakage by dropping the DMB bit when writing the page
protection bits to the CPU TLB.
In addition this patch adds a small optimization: if huge pages aren't
configured (which is at least the case for 32-bit kernels), then the
special bit is stored in the hpage (HUGE PAGE) bit instead. That way we
can skip to reset the DMB bit.
Fixes: df24e1783e6e ("parisc: Add vDSO support")
Cc: <stable@vger.kernel.org> # 5.18+
Signed-off-by: Helge Deller <deller@gmx.de>
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.