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Message-ID: <7249cb98-0b63-4ef6-8f6e-e29ac6c0a73f@flygoat.com>
Date: Fri, 22 Dec 2023 12:58:43 +0000
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Subject: Re: [PATCH 1/2] MIPS: Allow vectored interrupt handler to reside
 everywhere for 64bit
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To: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
 linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20231221125405.229100-1-tsbogend@alpha.franken.de>
From: Jiaxun Yang <jiaxun.yang@flygoat.com>
In-Reply-To: <20231221125405.229100-1-tsbogend@alpha.franken.de>
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在 2023/12/21 12:54, Thomas Bogendoerfer 写道:
> Setting up vector interrupts worked only with handlers, which resided
> in CKSEG0 space. This limits the kernel placement for 64bit platforms.
> By patching in the offset into vi_handlers[] instead of the full
> handler address, the vectored exception handler can load the
> address by itself and jump to it.
>
> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

Could you please keep me in Cc if you are going to propose a better
solution :-)

Thanks
- Jiaxun

> ---
>   arch/mips/kernel/genex.S | 8 ++++----
>   arch/mips/kernel/traps.c | 9 +++------
>   2 files changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
> index b6de8e88c1bd..a572ce36a24f 100644
> --- a/arch/mips/kernel/genex.S
> +++ b/arch/mips/kernel/genex.S
> @@ -272,18 +272,17 @@ NESTED(except_vec_vi, 0, sp)
>   	.set	push
>   	.set	noreorder
>   	PTR_LA	v1, except_vec_vi_handler
> -FEXPORT(except_vec_vi_lui)
> -	lui	v0, 0		/* Patched */
>   	jr	v1
>   FEXPORT(except_vec_vi_ori)
> -	 ori	v0, 0		/* Patched */
> +	 ori	v0, zero, 0		/* Offset in vi_handlers[] */
>   	.set	pop
>   	END(except_vec_vi)
>   EXPORT(except_vec_vi_end)
>   
>   /*
>    * Common Vectored Interrupt code
> - * Complete the register saves and invoke the handler which is passed in $v0
> + * Complete the register saves and invoke the handler, $v0 holds
> + * offset into vi_handlers[]
>    */
>   NESTED(except_vec_vi_handler, 0, sp)
>   	SAVE_TEMP
> @@ -331,6 +330,7 @@ NESTED(except_vec_vi_handler, 0, sp)
>   	/* Save task's sp on IRQ stack so that unwinding can follow it */
>   	LONG_S	s1, 0(sp)
>   2:
> +	PTR_L	v0, vi_handlers(v0)
>   	jalr	v0
>   
>   	/* Restore sp */
> diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
> index 246c6a6b0261..d90b18908692 100644
> --- a/arch/mips/kernel/traps.c
> +++ b/arch/mips/kernel/traps.c
> @@ -2091,16 +2091,14 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
>   		 * If no shadow set is selected then use the default handler
>   		 * that does normal register saving and standard interrupt exit
>   		 */
> -		extern const u8 except_vec_vi[], except_vec_vi_lui[];
> +		extern const u8 except_vec_vi[];
>   		extern const u8 except_vec_vi_ori[], except_vec_vi_end[];
>   		extern const u8 rollback_except_vec_vi[];
>   		const u8 *vec_start = using_rollback_handler() ?
>   				      rollback_except_vec_vi : except_vec_vi;
>   #if defined(CONFIG_CPU_MICROMIPS) || defined(CONFIG_CPU_BIG_ENDIAN)
> -		const int lui_offset = except_vec_vi_lui - vec_start + 2;
>   		const int ori_offset = except_vec_vi_ori - vec_start + 2;
>   #else
> -		const int lui_offset = except_vec_vi_lui - vec_start;
>   		const int ori_offset = except_vec_vi_ori - vec_start;
>   #endif
>   		const int handler_len = except_vec_vi_end - vec_start;
> @@ -2119,10 +2117,9 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
>   #else
>   				handler_len);
>   #endif
> -		h = (u16 *)(b + lui_offset);
> -		*h = (handler >> 16) & 0xffff;
> +		/* insert offset into vi_handlers[] */
>   		h = (u16 *)(b + ori_offset);
> -		*h = (handler & 0xffff);
> +		*h = n * sizeof(handler);
>   		local_flush_icache_range((unsigned long)b,
>   					 (unsigned long)(b+handler_len));
>   	}