linux-kernel - Re: [PATCH v1 2/8] powerpc/mem: Remove address argument to flush_coherent

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Date:   Thu, 08 Apr 2021 14:20:53 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/8] powerpc/mem: Remove address argument to
 flush_coherent_icache()

Christophe Leroy <christophe.leroy@...roup.eu> writes:

> flush_coherent_icache() can use any valid address as mentionned
> by the comment.
>
> Use PAGE_OFFSET as base address. This allows removing the
> user access stuff.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/mm/mem.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index ce6c81ce4362..19f807b87697 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -342,10 +342,9 @@ void free_initmem(void)
>  
>  /**
>   * flush_coherent_icache() - if a CPU has a coherent icache, flush it
> - * @addr: The base address to use (can be any valid address, the whole cache will be flushed)
>   * Return true if the cache was flushed, false otherwise
>   */
> -static inline bool flush_coherent_icache(unsigned long addr)
> +static inline bool flush_coherent_icache(void)
>  {
>  	/*
>  	 * For a snooping icache, we still need a dummy icbi to purge all the
> @@ -355,9 +354,7 @@ static inline bool flush_coherent_icache(unsigned long addr)
>  	 */
>  	if (cpu_has_feature(CPU_FTR_COHERENT_ICACHE)) {
>  		mb(); /* sync */
> -		allow_read_from_user((const void __user *)addr, L1_CACHE_BYTES);
> -		icbi((void *)addr);
> -		prevent_read_from_user((const void __user *)addr, L1_CACHE_BYTES);
> +		icbi((void *)PAGE_OFFSET);
>  		mb(); /* sync */
>  		isync();
>  		return true;

do we need that followup sync? Usermanual suggest sync; icbi(any address);
isync sequence. 

-aneesh