Re: linux-next: manual merge of the tip tree with the mm-hotfixes-unstable tree

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Tue, Jul 21, 2026 at 02:46:23PM +0100, Mark Brown wrote:
> Hi all,
>
> Today's linux-next merge of the tip tree got a conflict in:
>
>   arch/x86/mm/pat/set_memory.c
>
> between commit:
>
>   b8228ddfd0586 ("x86/mm/pat: allocate split page tables as kernel page tables")
>
> from the mm-hotfixes-unstable tree and commit:
>
>   5fce67641a3ed ("x86/mm/pat: Don't gate cpa_lock on debug_pagealloc_enabled()")
>
> from the tip tree.
>
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging.  You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.

Thanks, the resolution looks correct! :)

There's some discussion on the patches themselves but that's by-the-by.

Cheers, Lorenzo

>
> diff --cc arch/x86/mm/pat/set_memory.c
> index a67ca33b9dd12,1f2a2ba9ce57d..0000000000000
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@@ -439,26 -441,12 +442,28 @@@ static void __cpa_collapse_large_pages(
>
>   	list_for_each_entry_safe(ptdesc, tmp, &pgtables, pt_list) {
>   		list_del(&ptdesc->pt_list);
>  -		pagetable_free(ptdesc);
>  +
>  +		if (folio_test_pgtable(ptdesc_folio(ptdesc)))
>  +			pagetable_dtor_free(ptdesc);
>  +		else
>  +			pagetable_free(ptdesc);
>   	}
> +
> + 	spin_unlock(&cpa_lock);
>   }
>
>  +static void cpa_collapse_large_pages(struct cpa_data *cpa)
>  +{
>  +	/*
>  +	 * Take the mmap write lock on init_mm to:
>  +	 * - Avoid a use-after-free if raced by ptdump (which takes its own
>  +	 *   write lock on init_mm).
>  +	 * - Serialise concurrent CPA walkers.
>  +	 */
>  +	scoped_guard(mmap_write_lock, &init_mm)
>  +		__cpa_collapse_large_pages(cpa);
>  +}
>  +
>   static void cpa_flush(struct cpa_data *cpa, int cache)
>   {
>   	unsigned int i;
> @@@ -1249,18 -1237,16 +1253,16 @@@ __split_large_page(struct cpa_data *cpa
>   static int split_large_page(struct cpa_data *cpa, pte_t *kpte,
>   			    unsigned long address)
>   {
>  -	struct ptdesc *ptdesc;
>  +	pte_t *pte;
>
> - 	if (!debug_pagealloc_enabled())
> - 		spin_unlock(&cpa_lock);
> + 	spin_unlock(&cpa_lock);
>  -	ptdesc = pagetable_alloc(GFP_KERNEL, 0);
>  +	pte = pte_alloc_one_kernel(&init_mm);
> - 	if (!debug_pagealloc_enabled())
> - 		spin_lock(&cpa_lock);
> + 	spin_lock(&cpa_lock);
>  -	if (!ptdesc)
>  +	if (!pte)
>   		return -ENOMEM;
>
>  -	if (__split_large_page(cpa, kpte, address, ptdesc))
>  -		pagetable_free(ptdesc);
>  +	if (__split_large_page(cpa, kpte, address, pte))
>  +		pte_free_kernel(&init_mm, pte);
>
>   	return 0;
>   }