Re: [PATCH v1 03/16] arm64: hugetlb: Fix flush_hugetlb_tlb_range() invalidation level

[Ryan Roberts <ryan.roberts@arm.com>]

On 06/02/2025 06:46, Anshuman Khandual wrote:
> 
> 
> On 2/5/25 20:39, Ryan Roberts wrote:
>> commit c910f2b65518 ("arm64/mm: Update tlb invalidation routines for
>> FEAT_LPA2") changed the "invalidation level unknown" hint from 0 to
>> TLBI_TTL_UNKNOWN (INT_MAX). But the fallback "unknown level" path in
>> flush_hugetlb_tlb_range() was not updated. So as it stands, when trying
>> to invalidate CONT_PMD_SIZE or CONT_PTE_SIZE hugetlb mappings, we will
>> spuriously try to invalidate at level 0 on LPA2-enabled systems.
>>
>> Fix this so that the fallback passes TLBI_TTL_UNKNOWN, and while we are
>> at it, explicitly use the correct stride and level for CONT_PMD_SIZE and
>> CONT_PTE_SIZE, which should provide a minor optimization.
>>
>> Cc: <stable@vger.kernel.org>
>> Fixes: c910f2b65518 ("arm64/mm: Update tlb invalidation routines for FEAT_LPA2")
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> ---
>>  arch/arm64/include/asm/hugetlb.h | 20 ++++++++++++++------
>>  1 file changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
>> index 03db9cb21ace..8ab9542d2d22 100644
>> --- a/arch/arm64/include/asm/hugetlb.h
>> +++ b/arch/arm64/include/asm/hugetlb.h
>> @@ -76,12 +76,20 @@ static inline void flush_hugetlb_tlb_range(struct vm_area_struct *vma,
>>  {
>>  	unsigned long stride = huge_page_size(hstate_vma(vma));
>>  
>> -	if (stride == PMD_SIZE)
>> -		__flush_tlb_range(vma, start, end, stride, false, 2);
>> -	else if (stride == PUD_SIZE)
>> -		__flush_tlb_range(vma, start, end, stride, false, 1);
>> -	else
>> -		__flush_tlb_range(vma, start, end, PAGE_SIZE, false, 0);
>> +	switch (stride) {
>> +	case PUD_SIZE:
>> +		__flush_tlb_range(vma, start, end, PUD_SIZE, false, 1);
>> +		break;
> 
> Just wondering - should not !__PAGETABLE_PMD_FOLDED and pud_sect_supported()
> checks also be added here for this PUD_SIZE case ?

Yeah I guess so. TBH, it's never been entirely clear to me what the benefit is?
Is it just to remove (a tiny amount of) dead code when we know we don't support
blocks at the level? Or is there something more fundamental going on that I've
missed?

We seem to be quite inconsistent with the use of pud_sect_supported() in
hugetlbpage.c.

Anyway, I'll add this in, I guess it's preferable to follow the established pattern.

Thanks,
Ryan

> 
>> +	case CONT_PMD_SIZE:
>> +	case PMD_SIZE:
>> +		__flush_tlb_range(vma, start, end, PMD_SIZE, false, 2);
>> +		break;
>> +	case CONT_PTE_SIZE:
>> +		__flush_tlb_range(vma, start, end, PAGE_SIZE, false, 3);
>> +		break;
>> +	default:
>> +		__flush_tlb_range(vma, start, end, PAGE_SIZE, false, TLBI_TTL_UNKNOWN);
>> +	}
>>  }
>>  
>>  #endif /* __ASM_HUGETLB_H */