Re: [PATCH v2 27/47] mm/mmu_gather: fix flushing ranges with 4 GiB or larger

[David Hildenbrand (Arm)]

On 10/30/26 01:57, SJ Park wrote:
> On Thu, 29 Oct 2026 21:33:22 +0100 "David Hildenbrand (Arm)" <david@xxxxxxxxxx> wrote:
> 
>> From: Josef Bacik <josef@xxxxxxxxxxxxxx>
>>
>> __tlb_adjust_range() takes the size of the range which has to be flushed
>> as an unsigned int. Its callers, tlb_flush_{pte,pmd,pud,p4d}_range(), get
>> and pass an unsigned long. Consequently, a range that is 4 GiB or larger
>> gets truncated, possibly to 0.
>>
>> On arm64 with hugetlb, a 64k kernel can have 16 GiB hugetlb folios
>> mapped contiguously at the PMD level and flush them when unmapping, and a
>> 16k kernel can flush 64 GiB PUDs through tlb_unshare_pmd_ptdesc(). So
>> at least these two scenarios are affected.
>>
>> Fix it by flushing the proper range instead of the truncated one by
>> properly using "unsigned long" for range_size.
> 
> Makes sense to me.
> 
>>
>> Fix generated by an LLM and sent by Josef Bacik in private.
>>
>> Fixes: b528e4b6405b ("mm/hugetlb: add tlb_remove_hugetlb_entry for handling hugetlb pages")
>> Fixes: 8ce720d5bd91 ("mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
>> Acked-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
>> [ david: use two-tab indent, simplify description ]
> 
> It seems the convention [1] is to put the above modification note right before
> the last S-o-b: of David.  Maybe you forgot moving it after adding R-b: and
> T-b: from great reviewers?

It's "b4 trailers" that apparently messes this up. I don't think it really
matters (some move it above all trailers), but I'll fix this up when applying.

(++ on all the great people around here)

> 
>> Reviewed-by: Qi Zheng <qi.zheng@xxxxxxxxx>
>> Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
>> Tested-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
>> Reviewed-by: Dev Jain <dev.jain@xxxxxxx>
>> Reviewed-by: Muchun Song <muchun.song@xxxxxxxxx>
>> Reviewed-by: Pedro Falcato <pfalcato@xxxxxxx>
>> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> 
> Reviewed-by: SJ Park <sj@xxxxxxxxxx>
Thanks!

-- 
Cheers,

David