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

[David Hildenbrand (Arm)]

On 10/30/26 12:15, David Hildenbrand (Arm) wrote:
> 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.

Thinking again, I *think* this order is correct.

People reviewed and tested with these changes.

it would be something different if I modify a patch while applying it. Because
then, what people reviewed and tested would be different to the original version.

-- 
Cheers,

David