forked from Mirrors/opensbi
8153b2622b
This reverts commit 6966ad0abe ("platform/lib: Allow the OS to map the
regions that are protected by PMP").
It was thought at the time of this commit that allowing the kernel to map
PMP protected regions was safe but it is actually not: for example, the
hibernation process will try to access any linear mapping page and then
will fault on such mapped PMP regions [1]. Another issue is that the
device tree specification [2] states that a !no-map region must be
declared as EfiBootServicesData/Code in the EFI memory map which would make
the PMP protected regions reclaimable by the kernel. And to circumvent
this, RISC-V edk2 diverges from the DT specification to declare those
regions as EfiReserved.
The no-map attribute was removed to allow the kernel to use hugepages
larger than 2MB to map the linear mapping to improve the performance but
actually a recent talk from Mike Rapoport [3] stated that the
performance benefit was marginal.
For all those reasons, let's mark all the PMP protected regions as "no-map".
[1] https://lore.kernel.org/linux-riscv/CAAYs2=gQvkhTeioMmqRDVGjdtNF_vhB+vm_1dHJxPNi75YDQ_Q@mail.gmail.com/
[2] "3.5.4 /reserved-memory and UEFI" https://github.com/devicetree-org/devicetree-specification/releases/download/v0.4-rc1/devicetree-specification-v0.4-rc1.pdf
[3] https://lwn.net/Articles/931406/
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Xiang W <wxjstz@126.com>
35 lines
859 B
C
35 lines
859 B
C
/*
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* SPDX-License-Identifier: BSD-2-Clause
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*
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* Copyright (c) 2020 Western Digital Corporation or its affiliates.
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*
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* Authors:
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* Anup Patel <anup.patel@wdc.com>
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*/
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#include <platform_override.h>
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#include <sbi_utils/fdt/fdt_helper.h>
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#include <sbi_utils/fdt/fdt_fixup.h>
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static u64 sifive_fu540_tlbr_flush_limit(const struct fdt_match *match)
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{
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/*
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* The sfence.vma by virtual address does not work on
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* SiFive FU540 so we return remote TLB flush limit as zero.
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*/
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return 0;
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}
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static const struct fdt_match sifive_fu540_match[] = {
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{ .compatible = "sifive,fu540" },
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{ .compatible = "sifive,fu540g" },
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{ .compatible = "sifive,fu540-c000" },
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{ .compatible = "sifive,hifive-unleashed-a00" },
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{ },
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};
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const struct platform_override sifive_fu540 = {
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.match_table = sifive_fu540_match,
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.tlbr_flush_limit = sifive_fu540_tlbr_flush_limit,
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};
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