Re: [PATCH 1/3] MIPS: add missing MSACSR and upper MSA initialization

[Huacai Chen <chenhc@lemote.com>]

Hi, Pei,

On Fri, Aug 21, 2020 at 3:26 PM Huang Pei <huangpei@loongson.cn> wrote:
>
> own_fp_inatomic() does not restore/initialize MSACSR and upper MSA regs, so
> MSACSR and MSA upper regs's value from previous task on current cpu can leak
> into current task and cause unpredictable behavior when MSA context not
> initialized.
>
> Signed-off-by: Huang Pei <huangpei@loongson.cn>
> ---
>  arch/mips/kernel/traps.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
> index 38aa07ccdbcc..99a8f1b7b522 100644
> --- a/arch/mips/kernel/traps.c
> +++ b/arch/mips/kernel/traps.c
> @@ -1287,6 +1287,8 @@ static int enable_restore_fp_context(int msa)
>                 err = own_fpu_inatomic(1);
>                 if (msa && !err) {
>                         enable_msa();
> +                       write_msa_csr(current->thread.fpu.msacsr);
> +                       init_msa_upper();
I think write_msa_csr(current->thread.fpu.msacsr) is needed here, but
I don't know whether init_msa_upper() is also needed. Maybe you should
investegate cc97ab235f3fe32401ca198cebe6f42642e9 ("MIPS: Simplify FP
context initialization") which removes init_msa_upper().

Huacai
>                         set_thread_flag(TIF_USEDMSA);
>                         set_thread_flag(TIF_MSA_CTX_LIVE);
>                 }
> --
> 2.17.1
>