linux-kernel - Re: [PATCH v3 1/2] Introduce cpu_icache_is

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Message-ID: <dd3a1bed-e428-4ab7-8157-cca22db5067c@efficios.com>
Date: Sat, 7 Dec 2024 12:13:08 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, David Hildenbrand <david@...hat.com>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Miaohe Lin <linmiaohe@...wei.com>, Kefeng Wang <wangkefeng.wang@...wei.com>,
 John Hubbard <jhubbard@...dia.com>,
 "Huang, Ying" <ying.huang@...ux.alibaba.com>,
 Ryan Roberts <ryan.roberts@....com>, Alexander Potapenko
 <glider@...gle.com>, Kees Cook <keescook@...omium.org>,
 Vineet Gupta <vgupta@...nel.org>, linux-kernel@...r.kernel.org,
 linux-snps-arc@...ts.infradead.org, Dan Williams <dan.j.williams@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>,
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v3 1/2] Introduce cpu_icache_is_aliasing() across all
 architectures

On 2024-12-07 12:01, Mathieu Desnoyers wrote:
> On 2024-12-07 11:55, Zi Yan wrote:
>> In commit eacd0e950dc2 ("ARC: [mm] Lazy D-cache flush (non aliasing
>> VIPT)"), arc adds the need to flush dcache to make icache see the code
>> page change. This also requires special handling for
>> clear_user_(high)page(). Introduce cpu_icache_is_aliasing() to make
>> MM code query special clear_user_(high)page() easier. This will be used
>> by the following commit.
>>
>> Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> Signed-off-by: Zi Yan <ziy@...dia.com>
> 
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> 
We should probably use this new cpu_icache_is_aliasing() to gate
availability of DAX XIP, as described in the commit message here:

commit 8690bbcf3b ("Introduce cpu_dcache_is_aliasing() across all architectures)"

     Note that this leaves "cpu_icache_is_aliasing()" to be implemented as future
     work. This would be useful to gate features like XIP on architectures
     which have aliasing CPU dcache-icache but not CPU dcache-dcache.

Thanks,

Mathieu

>> ---
>>   arch/arc/Kconfig                 | 1 +
>>   arch/arc/include/asm/cachetype.h | 8 ++++++++
>>   include/linux/cacheinfo.h        | 6 ++++++
>>   3 files changed, 15 insertions(+)
>>   create mode 100644 arch/arc/include/asm/cachetype.h
>>
>> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
>> index 5b2488142041..e96935373796 100644
>> --- a/arch/arc/Kconfig
>> +++ b/arch/arc/Kconfig
>> @@ -6,6 +6,7 @@
>>   config ARC
>>       def_bool y
>>       select ARC_TIMERS
>> +    select ARCH_HAS_CPU_CACHE_ALIASING
>>       select ARCH_HAS_CACHE_LINE_SIZE
>>       select ARCH_HAS_DEBUG_VM_PGTABLE
>>       select ARCH_HAS_DMA_PREP_COHERENT
>> diff --git a/arch/arc/include/asm/cachetype.h 
>> b/arch/arc/include/asm/cachetype.h
>> new file mode 100644
>> index 000000000000..acd3b6cb4bf5
>> --- /dev/null
>> +++ b/arch/arc/include/asm/cachetype.h
>> @@ -0,0 +1,8 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef __ASM_ARC_CACHETYPE_H
>> +#define __ASM_ARC_CACHETYPE_H
>> +
>> +#define cpu_dcache_is_aliasing()    false
>> +#define cpu_icache_is_aliasing()    true
>> +
>> +#endif
>> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
>> index 108060612bb8..7ad736538649 100644
>> --- a/include/linux/cacheinfo.h
>> +++ b/include/linux/cacheinfo.h
>> @@ -155,8 +155,14 @@ static inline int get_cpu_cacheinfo_id(int cpu, 
>> int level)
>>   #ifndef CONFIG_ARCH_HAS_CPU_CACHE_ALIASING
>>   #define cpu_dcache_is_aliasing()    false
>> +#define cpu_icache_is_aliasing()    cpu_dcache_is_aliasing()
>>   #else
>>   #include <asm/cachetype.h>
>> +
>> +#ifndef cpu_icache_is_aliasing
>> +#define cpu_icache_is_aliasing()    cpu_dcache_is_aliasing()
>> +#endif
>> +
>>   #endif
>>   #endif /* _LINUX_CACHEINFO_H */
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com