Re: [PATCH 26/46] mm/mmu_gather: fix flushing ranges with 4 GiB or larger

[Gregory Price]

On 2026-10-27 00:17 +0100, David Hildenbrand (Arm) 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 flush 16 GiB hugetlb PMDs, 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.
> 
> 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 ]
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
Tested-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>

-- 
Gregory Price <gourry@xxxxxxxxxx>