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.

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;
  }

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;
>   }