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

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Date:   Thu, 8 Apr 2021 17:25:20 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        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()



Le 08/04/2021 à 10:50, Aneesh Kumar K.V a écrit :
> 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.

I don't know.

The original implementation is here: https://github.com/linuxppc/linux/commit/0ce636700

Christophe