linux-kernel - Re: [PATCH v12 5/5] arm64: Allow huge io mappings again

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Date:   Mon, 4 Jun 2018 19:12:57 +0530
From:   Chintan Pandya <cpandya@...eaurora.org>
To:     Will Deacon <will.deacon@....com>
Cc:     catalin.marinas@....com, mark.rutland@....com,
        akpm@...ux-foundation.org, toshi.kani@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 5/5] arm64: Allow huge io mappings again



On 6/4/2018 5:44 PM, Will Deacon wrote:
> On Fri, Jun 01, 2018 at 06:09:18PM +0530, Chintan Pandya wrote:
>> Huge mappings have had stability issues due to stale
>> TLB entry and memory leak issues. Since, those are
>> addressed in this series of patches, it is now safe
>> to allow huge mappings.
>>
>> Signed-off-by: Chintan Pandya <cpandya@...eaurora.org>
>> ---
>>   arch/arm64/mm/mmu.c | 18 ++----------------
>>   1 file changed, 2 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 6e7e16c..c65abc4 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -934,15 +934,8 @@ int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot)
>>   {
>>   	pgprot_t sect_prot = __pgprot(PUD_TYPE_SECT |
>>   					pgprot_val(mk_sect_prot(prot)));
>> -	pud_t new_pud = pfn_pud(__phys_to_pfn(phys), sect_prot);
>> -
>> -	/* Only allow permission changes for now */
>> -	if (!pgattr_change_is_safe(READ_ONCE(pud_val(*pudp)),
>> -				   pud_val(new_pud)))
>> -		return 0;
> 
> Do you actually need to remove these checks? If we're doing
> break-before-make properly, then the check won't fire but it would be
> good to keep it there so we can catch misuse of these in future.
> 
> In other words, can we drop this patch?

Yes, we don't need this patch as BBM is happening before this. I missed
that. I'll remove this patch in v13.

> 
> Will
> 

Chintan
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