[PATCH v3 04/23] iommu/pages: Make iommu_put_pages_list() work with high order allocations

[Baolu Lu]

On 2/26/25 03:39, Jason Gunthorpe wrote:
> alloc_pages_node(, order) needs to be paired with __free_pages(, order) to
> free all the allocated pages. For order != 0 the return from
> alloc_pages_node() is just a page list, it hasn't been formed into a
> folio.
> 
> However iommu_put_pages_list() just calls put_page() on the head page of
> an allocation, which will end up leaking the tail pages if order != 0.
> 
> Fix this by using __GFP_COMP to create a high order folio and then always
> use put_page() to free the full high order folio.
> 
> __iommu_free_account() can get the order of the allocation via
> folio_order(), which corrects the accounting of high order allocations in
> iommu_put_pages_list(). This is the same technique slub uses.
> 
> As far as I can tell, none of the places using high order allocations are
> also using the free list, so this not a current bug.
> 
> Fixes: 06c375053cef ("iommu/vt-d: add wrapper functions for page allocations")
> Signed-off-by: Jason Gunthorpe<jgg at nvidia.com>

Reviewed-by: Lu Baolu <baolu.lu at linux.intel.com>