linux-kernel - Re: [PATCH 1/2] riscv: misaligned: Add handling for ZCB instructions

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Message-ID: <c7941874-758b-49eb-af58-23c371b7d1e8@ghiti.fr>
Date: Mon, 21 Apr 2025 09:47:44 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Nylon Chen <nylon.chen@...ive.com>, linux-kernel@...r.kernel.org
Cc: linux-riscv@...ts.infradead.org, paul.walmsley@...ive.com,
 palmer@...belt.com, aou@...s.berkeley.edu, charlie@...osinc.com,
 jesse@...osinc.com, evan@...osinc.com, cleger@...osinc.com,
 zhangchunyan@...as.ac.cn, samuel.holland@...ive.com, zong.li@...ive.com
Subject: Re: [PATCH 1/2] riscv: misaligned: Add handling for ZCB instructions

Hi Nylon,

On 11/04/2025 09:38, Nylon Chen wrote:
> Add support for the Zcb extension's compressed half-word instructions
> (C.LHU, C.LH, and C.SH) in the RISC-V misaligned access trap handler.
>
> Signed-off-by: Zong Li <zong.li@...ive.com>
> Signed-off-by: Nylon Chen <nylon.chen@...ive.com>


I would add the following fixes tag:

Fixes: 956d705dd279 ("riscv: Unaligned load/store handling for M_MODE")


> ---
>   arch/riscv/kernel/traps_misaligned.c | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
>
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index 7cc108aed74e..d7275dfb6b7e 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -88,6 +88,13 @@
>   #define INSN_MATCH_C_FSWSP		0xe002
>   #define INSN_MASK_C_FSWSP		0xe003
>   
> +#define INSN_MATCH_C_LHU		0x8400
> +#define INSN_MASK_C_LHU			0xfc43
> +#define INSN_MATCH_C_LH			0x8440
> +#define INSN_MASK_C_LH			0xfc43
> +#define INSN_MATCH_C_SH			0x8c00
> +#define INSN_MASK_C_SH			0xfc43
> +
>   #define INSN_LEN(insn)			((((insn) & 0x3) < 0x3) ? 2 : 4)
>   
>   #if defined(CONFIG_64BIT)
> @@ -431,6 +438,13 @@ static int handle_scalar_misaligned_load(struct pt_regs *regs)
>   		fp = 1;
>   		len = 4;
>   #endif
> +	} else if ((insn & INSN_MASK_C_LHU) == INSN_MATCH_C_LHU) {
> +		len = 2;
> +		insn = RVC_RS2S(insn) << SH_RD;
> +	} else if ((insn & INSN_MASK_C_LH) == INSN_MATCH_C_LH) {
> +		len = 2;
> +		shift = 8 * (sizeof(ulong) - len);
> +		insn = RVC_RS2S(insn) << SH_RD;
>   	} else {
>   		regs->epc = epc;
>   		return -1;
> @@ -530,6 +544,9 @@ static int handle_scalar_misaligned_store(struct pt_regs *regs)
>   		len = 4;
>   		val.data_ulong = GET_F32_RS2C(insn, regs);
>   #endif
> +	} else if ((insn & INSN_MASK_C_SH) == INSN_MATCH_C_SH) {
> +		len = 2;
> +		val.data_ulong = GET_RS2S(insn, regs);
>   	} else {
>   		regs->epc = epc;
>   		return -1;


Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks,

Alex