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Subject: Re: [PATCH v5 1/5] powerpc/sstep: Emulate prefixed instructions only
 when CPU_FTR_ARCH_31 is set
To: Ravi Bangoria <ravi.bangoria@linux.ibm.com>, bala24@linux.ibm.com
References: <20201011050908.72173-1-ravi.bangoria@linux.ibm.com>
 <20201011050908.72173-2-ravi.bangoria@linux.ibm.com>
From: Sandipan Das <sandipan@linux.ibm.com>
Message-ID: <01733550-9581-a894-be11-dd0b5991d306@linux.ibm.com>
Date: Sun, 11 Oct 2020 20:36:22 +0530
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On 11/10/20 10:39 am, Ravi Bangoria wrote:
> From: Balamuruhan S <bala24@linux.ibm.com>
> 
> Unconditional emulation of prefixed instructions will allow
> emulation of them on Power10 predecessors which might cause
> issues. Restrict that.
> 
> Fixes: 3920742b92f5 ("powerpc sstep: Add support for prefixed fixed-point arithmetic")
> Fixes: 50b80a12e4cc ("powerpc sstep: Add support for prefixed load/stores")
> Signed-off-by: Balamuruhan S <bala24@linux.ibm.com>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
> ---
>  arch/powerpc/lib/sstep.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index e9dcaba9a4f8..e6242744c71b 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -1346,6 +1346,9 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
>  	switch (opcode) {
>  #ifdef __powerpc64__
>  	case 1:
> +		if (!cpu_has_feature(CPU_FTR_ARCH_31))
> +			return -1;
> +
>  		prefix_r = GET_PREFIX_R(word);
>  		ra = GET_PREFIX_RA(suffix);
>  		rd = (suffix >> 21) & 0x1f;
> @@ -2733,6 +2736,9 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
>  		}
>  		break;
>  	case 1: /* Prefixed instructions */
> +		if (!cpu_has_feature(CPU_FTR_ARCH_31))
> +			return -1;
> +
>  		prefix_r = GET_PREFIX_R(word);
>  		ra = GET_PREFIX_RA(suffix);
>  		op->update_reg = ra;
> 

LGTM

Reviewed-by: Sandipan Das <sandipan@linux.ibm.com>