From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Price <steven.price@arm.com>
Subject: Re: [PATCH v5 21/25] mm: Add arch hooks for saving/restoring tags
Date: Thu, 25 Jun 2020 10:04:59 +0100
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References: <20200624175244.25837-1-catalin.marinas@arm.com>
 <20200624175244.25837-22-catalin.marinas@arm.com>
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To: Andrew Morton <akpm@linux-foundation.org>, Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon <will@kernel.org>, Dave P Martin <Dave.Martin@arm.com>, Vincenzo Frascino <vincenzo.frascino@arm.com>, Szabolcs Nagy <szabolcs.nagy@arm.com>, Kevin Brodsky <kevin.brodsky@arm.com>, Andrey Konovalov <andreyknvl@google.com>, Peter Collingbourne <pcc@google.com>

On 24/06/2020 19:45, Andrew Morton wrote:
> On Wed, 24 Jun 2020 18:52:40 +0100 Catalin Marinas <catalin.marinas@arm.com> wrote:
> 
>> From: Steven Price <steven.price@arm.com>
>>
>> Arm's Memory Tagging Extension (MTE) adds some metadata (tags) to
>> every physical page, when swapping pages out to disk it is necessary to
>> save these tags, and later restore them when reading the pages back.
>>
>> Add some hooks along with dummy implementations to enable the
>> arch code to handle this.
>>
>> Three new hooks are added to the swap code:
>>   * arch_prepare_to_swap() and
>>   * arch_swap_invalidate_page() / arch_swap_invalidate_area().
>> One new hook is added to shmem:
>>   * arch_swap_restore_tags()
>>
>> ...
>>
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -631,6 +631,29 @@ static inline int arch_unmap_one(struct mm_struct *mm,
>>   }
>>   #endif
>>   
>> +#ifndef __HAVE_ARCH_PREPARE_TO_SWAP
>> +static inline int arch_prepare_to_swap(struct page *page)
>> +{
>> +	return 0;
>> +}
>> +#endif
>> +
>> +#ifndef __HAVE_ARCH_SWAP_INVALIDATE
>> +static inline void arch_swap_invalidate_page(int type, pgoff_t offset)
>> +{
>> +}
>> +
>> +static inline void arch_swap_invalidate_area(int type)
>> +{
>> +}
>> +#endif
>> +
>> +#ifndef __HAVE_ARCH_SWAP_RESTORE_TAGS
>> +static inline void arch_swap_restore_tags(swp_entry_t entry, struct page *page)
>> +{
>> +}
>> +#endif
> 
> Presumably these three __HAVE_ARCH_ macros are to be defined in asm/pgtable.h?

That would be the idea (see patch 22). However:

Catalin - you've renamed __HAVE_ARCH_SWAP_RESTORE_TAGS in patch 22, but 
not here!

Steve