linux-kernel - Re: [PATCH 03/15] MIPS: pm-cps: Avoid offset overflow on MIPSr6

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Date:	Wed, 3 Feb 2016 14:48:39 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Paul Burton <paul.burton@...tec.com>
CC:	<linux-mips@...ux-mips.org>, Ralf Baechle <ralf@...ux-mips.org>,
	"Markos Chandras" <markos.chandras@...tec.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/15] MIPS: pm-cps: Avoid offset overflow on MIPSr6

On Wed, Feb 03, 2016 at 03:15:23AM +0000, Paul Burton wrote:
> From: Markos Chandras <markos.chandras@...tec.com>
> 
> This is similar to commit 934c79231c1b ("MIPS: asm: r4kcache: Add MIPS
> R6 cache unroll functions"). The CACHE instruction has been redefined
> for MIPSr6 and it reduced its offset field to 8 bits. This leads to
> micro-assembler field overflow warnings when booting SMP MIPSr6 cores
> like the following one:
> 
> Call Trace:
> [<ffffffff8010af88>] show_stack+0x68/0x88
> [<ffffffff8056ddf0>] dump_stack+0x68/0x88
> [<ffffffff801305bc>] warn_slowpath_common+0x8c/0xc8
> [<ffffffff80130630>] warn_slowpath_fmt+0x38/0x48
> [<ffffffff80125814>] build_insn+0x514/0x5c0
> [<ffffffff806ee134>] cps_gen_cache_routine.isra.3+0xe0/0x1b8
> [<ffffffff806ee570>] cps_pm_init+0x364/0x9ec
> [<ffffffff80100538>] do_one_initcall+0x90/0x1a8
> [<ffffffff806e8c14>] kernel_init_freeable+0x160/0x21c
> [<ffffffff8056b6a0>] kernel_init+0x10/0xf8
> [<ffffffff801059f8>] ret_from_kernel_thread+0x14/0x1c
> 
> We fix this by incrementing the base register on every loop.
> 
> Signed-off-by: Markos Chandras <markos.chandras@...tec.com>
> Signed-off-by: Paul Burton <paul.burton@...tec.com>
> ---
> 
>  arch/mips/kernel/pm-cps.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/mips/kernel/pm-cps.c b/arch/mips/kernel/pm-cps.c
> index f63a289..524ba11 100644
> --- a/arch/mips/kernel/pm-cps.c
> +++ b/arch/mips/kernel/pm-cps.c
> @@ -224,11 +224,18 @@ static void __init cps_gen_cache_routine(u32 **pp, struct uasm_label **pl,
>  	uasm_build_label(pl, *pp, lbl);
>  
>  	/* Generate the cache ops */
> -	for (i = 0; i < unroll_lines; i++)
> -		uasm_i_cache(pp, op, i * cache->linesz, t0);
> +	for (i = 0; i < unroll_lines; i++) {

Maybe worth adding a comment here to mention different immediate field
size in r6 encodings, otherwise it could look a bit mysterious to the
reader.

Cheers
James

> +		if (cpu_has_mips_r6) {
> +			uasm_i_cache(pp, op, 0, t0);
> +			uasm_i_addiu(pp, t0, t0, cache->linesz);
> +		} else {
> +			uasm_i_cache(pp, op, i * cache->linesz, t0);
> +		}
> +	}
>  
> -	/* Update the base address */
> -	uasm_i_addiu(pp, t0, t0, unroll_lines * cache->linesz);
> +	if (!cpu_has_mips_r6)
> +		/* Update the base address */
> +		uasm_i_addiu(pp, t0, t0, unroll_lines * cache->linesz);
>  
>  	/* Loop if we haven't reached the end address yet */
>  	uasm_il_bne(pp, pr, t0, t1, lbl);
> -- 
> 2.7.0
> 
> 

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