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[ Upstream commitb7795074a0] On parisc a spinlock is stored in the next page behind the pgd which protects against parallel accesses to the pgd. That's why one additional page (PGD_ALLOC_ORDER) is allocated for the pgd. Matthew Wilcox suggested that we instead should use a pointer in the struct page table for this spinlock and noted, that the comments for the PGD_ORDER and PMD_ORDER defines were wrong. Both suggestions are addressed with this patch. Instead of having an own spinlock to protect the pgd, we now switch to use the existing page_table_lock. Additionally, beside loading the pgd into cr25 in switch_mm_irqs_off(), the physical address of this lock is loaded into cr28 (tr4), so that we can avoid implementing a complicated lookup in assembly for this lock in the TLB fault handlers. The existing Hybrid L2/L3 page table scheme (where the pmd is adjacent to the pgd) has been dropped with this patch. Remove the locking in set_pte() and the huge-page pte functions too. They trigger a spinlock recursion on 32bit machines and seem unnecessary. Suggested-by: Matthew Wilcox <willy@infradead.org> Fixes:b37d1c1898("parisc: Use per-pagetable spinlock") Signed-off-by: John David Anglin <dave.anglin@bell.net> Signed-off-by: Helge Deller <deller@gmx.de> Stable-dep-of:38860b2c8b("parisc: Flush kernel data mapping in set_pte_at() when installing pte for user page") Signed-off-by: Sasha Levin <sashal@kernel.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.