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SubjectRe: [PATCH v9 16/17] riscv: Fix an illegal instruction exception when accessing vlenb without enable vector first
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On 09/11/2021 09:48, Greentime Hu wrote:
> It triggered an illegal instruction exception when accessing vlenb CSR
> without enable vector first. To fix this issue, we should enable vector
> before using it and disable vector after using it.
>
> Co-developed-by: Vincent Chen <vincent.chen@sifive.com>
> Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
> Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
> ---
> arch/riscv/include/asm/vector.h | 2 ++
> arch/riscv/kernel/cpufeature.c | 2 ++
> arch/riscv/kernel/kernel_mode_vector.c | 6 ++++--
> 3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
> index 5d7f14453f68..ca063c8f47f2 100644
> --- a/arch/riscv/include/asm/vector.h
> +++ b/arch/riscv/include/asm/vector.h
> @@ -8,6 +8,8 @@
>
> #include <linux/types.h>
>
> +void rvv_enable(void);
> +void rvv_disable(void);
> void kernel_rvv_begin(void);
> void kernel_rvv_end(void);
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 8e7557980faf..0139ec20adce 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -159,7 +159,9 @@ void __init riscv_fill_hwcap(void)
> if (elf_hwcap & COMPAT_HWCAP_ISA_V) {
> static_branch_enable(&cpu_hwcap_vector);
> /* There are 32 vector registers with vlenb length. */
> + rvv_enable();
> riscv_vsize = csr_read(CSR_VLENB) * 32;
> + rvv_disable();
> }
> #endif

Would it be better to enable this here, and then restore the original
state instead of calling rvv_disable? If it was enabled then maybe
something else is going to rely on that state?

Maybe something like:

prev = rvv_enable()
riscv_vsize = csr_read(CSR_VLENB) * 32;
rvv_restore(prev);


> }
> diff --git a/arch/riscv/kernel/kernel_mode_vector.c b/arch/riscv/kernel/kernel_mode_vector.c
> index 8d2e53ea25c1..1ecb6ec5c56d 100644
> --- a/arch/riscv/kernel/kernel_mode_vector.c
> +++ b/arch/riscv/kernel/kernel_mode_vector.c
> @@ -71,15 +71,17 @@ static void put_cpu_vector_context(void)
> preempt_enable();
> }
>
> -static void rvv_enable(void)
> +void rvv_enable(void)
> {
> csr_set(CSR_STATUS, SR_VS);
> }
> +EXPORT_SYMBOL(rvv_enable);
>
> -static void rvv_disable(void)
> +void rvv_disable(void)
> {
> csr_clear(CSR_STATUS, SR_VS);
> }
> +EXPORT_SYMBOL(rvv_disable);
>
> /*
> * kernel_rvv_begin(): obtain the CPU vector registers for use by the calling
>


--
Ben Dooks http://www.codethink.co.uk/
Senior Engineer Codethink - Providing Genius

https://www.codethink.co.uk/privacy.html

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