linux-kernel - Re: [PATCH] MIPS: KASLR: Fix sync_icache() trapped in loop when synci

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Date:   Wed, 2 Dec 2020 11:39:43 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Jinyang He <hejinyang@...ngson.cn>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: KASLR: Fix sync_icache() trapped in loop when
 synci_step is zero

On Wed, Dec 02, 2020 at 11:00:05AM +0800, Jinyang He wrote:
> Reading synci_step by using rdhwr instruction may return zero if no cache
> need be synchronized. On the one hand, to make sure all load operation and
> store operation finished we do __sync() for every platform. On the other
> hand, some platform need operate synci one time although step is zero.

Should this be someting like: Avoid endless loop, if no synci is needed ?

> diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
> index 57bdd276..47aeb33 100644
> --- a/arch/mips/kernel/relocate.c
> +++ b/arch/mips/kernel/relocate.c
> @@ -64,7 +64,7 @@ static void __init sync_icache(void *kbase, unsigned long kernel_length)
>  			: "r" (kbase));
>  
>  		kbase += step;
> -	} while (kbase < kend);
> +	} while (step && kbase < kend);

why not do a

	if (step == 0)
		return;

before entering the loop ? According to MIPS32PRA no synci is needed,
if stepi value is zero.

Thomas.

PS: Does anybody know a reason, why this code doesn't use an old fashioned
dache/icache flushing, which might be slower but would work also on
legecy cores ?

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]