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This patch utilizes Vector to perform copy_to_user/copy_from_user. If Vector is available and the size of copy is large enough for Vector to perform better than scalar, then direct the kernel to do Vector copies for userspace. Though the best programming practice for users is to reduce the copy, this provides a faster variant when copies are inevitable. The optimal size for using Vector, copy_to_user_thres, is only a heuristic for now. We can add DT parsing if people feel the need of customizing it. The exception fixup code of the __asm_vector_usercopy must fallback to the scalar one because accessing user pages might fault, and must be sleepable. Current kernel-mode Vector does not allow tasks to be preemptible, so we must disactivate Vector and perform a scalar fallback in such case. The original implementation of Vector operations comes from https://github.com/sifive/sifive-libc, which we agree to contribute to Linux kernel. Co-developed-by: Jerry Shih <jerry.shih@sifive.com> Signed-off-by: Jerry Shih <jerry.shih@sifive.com> Co-developed-by: Nick Knight <nick.knight@sifive.com> Signed-off-by: Nick Knight <nick.knight@sifive.com> Suggested-by: Guo Ren <guoren@kernel.org> Signed-off-by: Andy Chiu <andy.chiu@sifive.com> Tested-by: Björn Töpel <bjorn@rivosinc.com> Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> Link: https://lore.kernel.org/r/20240115055929.4736-6-andy.chiu@sifive.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
46 lines
977 B
C
46 lines
977 B
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Copyright (C) 2023 SiFive
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* Author: Andy Chiu <andy.chiu@sifive.com>
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*/
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#include <linux/linkage.h>
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#include <asm/asm.h>
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#include <asm/vector.h>
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#include <asm/simd.h>
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#ifdef CONFIG_MMU
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#include <asm/asm-prototypes.h>
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#endif
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#ifdef CONFIG_MMU
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size_t riscv_v_usercopy_threshold = CONFIG_RISCV_ISA_V_UCOPY_THRESHOLD;
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int __asm_vector_usercopy(void *dst, void *src, size_t n);
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int fallback_scalar_usercopy(void *dst, void *src, size_t n);
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asmlinkage int enter_vector_usercopy(void *dst, void *src, size_t n)
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{
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size_t remain, copied;
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/* skip has_vector() check because it has been done by the asm */
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if (!may_use_simd())
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goto fallback;
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kernel_vector_begin();
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remain = __asm_vector_usercopy(dst, src, n);
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kernel_vector_end();
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if (remain) {
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copied = n - remain;
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dst += copied;
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src += copied;
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n = remain;
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goto fallback;
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}
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return remain;
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fallback:
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return fallback_scalar_usercopy(dst, src, n);
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}
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#endif
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