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In order to implement fast gup we need to ensure that the page table walker is protected from page table pages being freed from under it. riscv situation is more complicated than other architectures: some riscv platforms may use IPI to perform TLB shootdown, for example, those platforms which support AIA, usually the riscv_ipi_for_rfence is true on these platforms; some riscv platforms may rely on the SBI to perform TLB shootdown, usually the riscv_ipi_for_rfence is false on these platforms. To keep software pagetable walkers safe in this case we switch to RCU based table free (MMU_GATHER_RCU_TABLE_FREE). See the comment below 'ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE' in include/asm-generic/tlb.h for more details. This patch enables MMU_GATHER_RCU_TABLE_FREE, then use *tlb_remove_page_ptdesc() for those platforms which use IPI to perform TLB shootdown; *tlb_remove_ptdesc() for those platforms which use SBI to perform TLB shootdown; Both case mean that disabling interrupts will block the free and protect the fast gup page walker. Signed-off-by: Jisheng Zhang <jszhang@kernel.org> Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20231219175046.2496-4-jszhang@kernel.org Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
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.