[PATCH] platform: generic: thead: fix stale TLB entries for th1520/sg2042

[Jessica Clarke]

On 14 Sep 2023, at 05:27, Inochi Amaoto <inochiama at outlook.com> wrote:
> 
> The TLB entries remain functional all the time once added in T-HEAD th1520
> and Sophgo sg2042 even if the MMU is then disabled afterwards. If there
> are some stale TLB entries that contains the address of SBI, it will cause
> unexpected memory access and issue a illegal instruction error. To avoid
> this, a TLB flush is needed to drop these TLB entries before any memory
> access in the trap handler.

Another thought: is this just the DTLB, or is the ITLB also affected?
Because if the ITLB is affected then there’s no guarantee there isn’t
an entry for the trap handler’s address that gets used and stops the
trap handler from running? Not that you could really do anything in that
case, you’d just be hosed and need a chip that isn’t broken.

Jess

> To handle this workaroud, add a custom trap handler with executing TLB flush
> first in the T-HEAD platform to fix affected socs.
> 
> Signed-off-by: Inochi Amaoto <inochiama at outlook.com>
> ---
> Changed from RFC v2:
> 1. rollback the moving of trap helper macro to sbi_trap.h
> 2. use direct jump in custom trap handler to access _trap_handler
> 
> Changed from RFC:
> 1. use custom trap handler instead of asm alternative.
> 2. change description
> 
> ---
> platform/generic/Kconfig                    |  4 ++
> platform/generic/configs/defconfig          |  1 +
> platform/generic/thead/objects.mk           | 10 ++++
> platform/generic/thead/thead-generic.c      | 57 +++++++++++++++++++++
> platform/generic/thead/thead-trap-handler.S | 17 ++++++
> 5 files changed, 89 insertions(+)
> create mode 100644 platform/generic/thead/objects.mk
> create mode 100644 platform/generic/thead/thead-generic.c
> create mode 100644 platform/generic/thead/thead-trap-handler.S
> 
> diff --git a/platform/generic/Kconfig b/platform/generic/Kconfig
> index 72768ed..68dd58c 100644
> --- a/platform/generic/Kconfig
> +++ b/platform/generic/Kconfig
> @@ -52,6 +52,10 @@ config PLATFORM_STARFIVE_JH7110
> bool "StarFive JH7110 support"
> default n
> 
> +config PLATFORM_THEAD_GENERIC
> + bool "THEAD C9xx generic platform support"
> + default n
> +
> source "$(OPENSBI_SRC_DIR)/platform/generic/andes/Kconfig"
> 
> endif
> diff --git a/platform/generic/configs/defconfig b/platform/generic/configs/defconfig
> index 634d410..26f0874 100644
> --- a/platform/generic/configs/defconfig
> +++ b/platform/generic/configs/defconfig
> @@ -4,6 +4,7 @@ CONFIG_PLATFORM_RENESAS_RZFIVE=y
> CONFIG_PLATFORM_SIFIVE_FU540=y
> CONFIG_PLATFORM_SIFIVE_FU740=y
> CONFIG_PLATFORM_STARFIVE_JH7110=y
> +CONFIG_PLATFORM_THEAD_GENERIC=y
> CONFIG_FDT_GPIO=y
> CONFIG_FDT_GPIO_DESIGNWARE=y
> CONFIG_FDT_GPIO_SIFIVE=y
> diff --git a/platform/generic/thead/objects.mk b/platform/generic/thead/objects.mk
> new file mode 100644
> index 0000000..cbbab18
> --- /dev/null
> +++ b/platform/generic/thead/objects.mk
> @@ -0,0 +1,10 @@
> +#
> +# SPDX-License-Identifier: BSD-2-Clause
> +#
> +# Copyright (C) 2023 Inochi Amaoto <inochiama at outlook.com>
> +# Copyright (C) 2023 Alibaba Group Holding Limited.
> +#
> +
> +carray-platform_override_modules-$(CONFIG_PLATFORM_THEAD_GENERIC) += thead_generic
> +platform-objs-$(CONFIG_PLATFORM_THEAD_GENERIC) += thead/thead-generic.o
> +platform-objs-$(CONFIG_PLATFORM_THEAD_GENERIC) += thead/thead-trap-handler.o
> diff --git a/platform/generic/thead/thead-generic.c b/platform/generic/thead/thead-generic.c
> new file mode 100644
> index 0000000..6cbe44c
> --- /dev/null
> +++ b/platform/generic/thead/thead-generic.c
> @@ -0,0 +1,57 @@
> +/*
> + * SPDX-License-Identifier: BSD-2-Clause
> + *
> + * Authors:
> + *   Inochi Amaoto <inochiama at outlook.com>
> + *
> + */
> +
> +#include <platform_override.h>
> +#include <sbi/riscv_barrier.h>
> +#include <sbi/sbi_const.h>
> +#include <sbi/sbi_platform.h>
> +#include <sbi/sbi_scratch.h>
> +#include <sbi/sbi_string.h>
> +#include <sbi_utils/fdt/fdt_helper.h>
> +
> +#define THEAD_QUIRK_SFENCE_FIXUP BIT(0)
> +
> +#define thead_get_symbol_local_address(_name) \
> + ({ \
> + register unsigned long __v; \
> + __asm__ __volatile__ ("lla %0, " STRINGIFY(_name) \
> +     : "=r"(__v) \
> +     : \
> +     : "memory"); \
> + (void*)__v; \
> + })
> +
> +void thead_register_sfence_trap_handler(void)
> +{
> + void* trap_hanlder_addr = thead_get_symbol_local_address(
> + _thead_sfence_trap_handler);
> +
> + csr_write(CSR_MTVEC, trap_hanlder_addr);
> +}
> +
> +static int thead_generic_early_init(bool cold_boot,
> +    const struct fdt_match *match)
> +{
> + unsigned long quirks = (unsigned long)match->data;
> +
> + if (quirks & THEAD_QUIRK_SFENCE_FIXUP)
> + thead_register_sfence_trap_handler();
> +
> + return 0;
> +}
> +
> +static const struct fdt_match thead_generic_match[] = {
> + { .compatible = "thead,th1520",
> +  .data = (void*)THEAD_QUIRK_SFENCE_FIXUP },
> + { },
> +};
> +
> +const struct platform_override thead_generic = {
> + .match_table = thead_generic_match,
> + .early_init = thead_generic_early_init,
> +};
> diff --git a/platform/generic/thead/thead-trap-handler.S b/platform/generic/thead/thead-trap-handler.S
> new file mode 100644
> index 0000000..6c99f32
> --- /dev/null
> +++ b/platform/generic/thead/thead-trap-handler.S
> @@ -0,0 +1,17 @@
> +/*
> + * SPDX-License-Identifier: BSD-2-Clause
> + *
> + * Authors:
> + *   Inochi Amaoto <inochiama at outlook.com>
> + *
> + */
> +
> +#include <sbi/riscv_elf.h>
> +#include <sbi/sbi_trap.h>
> +
> + .section .entry, "ax", %progbits
> + .align 3
> + .globl _thead_sfence_trap_handler
> +_thead_sfence_trap_handler:
> + sfence.vma t0, zero
> + j _trap_handler
> --
> 2.42.0
>