From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Price <steven.price@arm.com>
Subject: Re: [PATCH 3/4] arm64: mte: Enable swap of tagged pages
Date: Mon, 4 May 2020 13:53:23 +0100
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References: <20200422142530.32619-1-steven.price@arm.com>
 <20200422142530.32619-4-steven.price@arm.com> <20200503152858.GA11959@gaia>
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To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>, Arnd Bergmann <arnd@arndb.de>, Hugh Dickins <hughd@google.com>, Vincenzo Frascino <vincenzo.frascino@arm.com>, Will Deacon <will@kernel.org>

On 03/05/2020 16:29, Catalin Marinas wrote:
> On Wed, Apr 22, 2020 at 03:25:29PM +0100, Steven Price wrote:
>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
>> index 39a372bf8afc..a4ad1b75a1a7 100644
>> --- a/arch/arm64/include/asm/pgtable.h
>> +++ b/arch/arm64/include/asm/pgtable.h
>> @@ -80,6 +80,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
>>   #define pte_user_exec(pte)	(!(pte_val(pte) & PTE_UXN))
>>   #define pte_cont(pte)		(!!(pte_val(pte) & PTE_CONT))
>>   #define pte_devmap(pte)		(!!(pte_val(pte) & PTE_DEVMAP))
>> +#define pte_tagged(pte)		(!!((pte_val(pte) & PTE_ATTRINDX_MASK) == \
>> +				    PTE_ATTRINDX(MT_NORMAL_TAGGED)))
>>   
>>   #define pte_cont_addr_end(addr, end)						\
>>   ({	unsigned long __boundary = ((addr) + CONT_PTE_SIZE) & CONT_PTE_MASK;	\
>> @@ -268,12 +270,17 @@ static inline void __check_racy_pte_update(struct mm_struct *mm, pte_t *ptep,
>>   		     __func__, pte_val(old_pte), pte_val(pte));
>>   }
>>   
>> +void mte_sync_tags(pte_t *ptep, pte_t pte);
>> +
>>   static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
>>   			      pte_t *ptep, pte_t pte)
>>   {
>>   	if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))
>>   		__sync_icache_dcache(pte);
>>   
>> +	if (system_supports_mte() && pte_tagged(pte))
>> +		mte_sync_tags(ptep, pte);
> 
> I think this needs a pte_present() check as well, otherwise pte_tagged()
> could match some random swap entry.

Good spot - mte_sync_tags() bails out fairly early in this case (which 
explains why I didn't see any problems). But it's *after* PG_mte_tagged 
is set which will lead to incorrectly flagging pages.

Thanks,

Steve