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commitf79ad50ea3upstream. When using the radix MMU on Power9 DD1, to work around a hardware problem, radix__pte_update() is required to do a two stage update of the PTE. First we write a zero value into the PTE, then we flush the TLB, and then we write the new PTE value. In the normal case that works OK, but it does not work if we're updating the PTE that maps the code we're executing, because the mapping is removed by the TLB flush and we can no longer execute from it. Unfortunately the STRICT_RWX code needs to do exactly that. The exact symptoms when we hit this case vary, sometimes we print an oops and then get stuck after that, but I've also seen a machine just get stuck continually page faulting with no oops printed. The variance is presumably due to the exact layout of the text and the page size used for the mappings. In all cases we are unable to boot to a shell. There are possible solutions such as creating a second mapping of the TLB flush code, executing from that, and then jumping back to the original. However we don't want to add that level of complexity for a DD1 work around. So just detect that we're running on Power9 DD1 and refrain from changing the permissions, effectively disabling STRICT_RWX on Power9 DD1. Fixes:7614ff3272("powerpc/mm/radix: Implement STRICT_RWX/mark_rodata_ro() for Radix") Reported-by: Andrew Jeffery <andrew@aj.id.au> [Changelog as suggested by Michael Ellerman <mpe@ellerman.id.au>] Signed-off-by: Balbir Singh <bsingharora@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.