[PATCH v2 0/3] Convert 64-bit x86/mm/pat to ptdescs

[PATCH v2 0/3] Convert 64-bit x86/mm/pat to ptdescs

[Vishal Moola (Oracle)]

x86/mm/pat should be using ptdescs. One line has already been
converted to pagetable_free(), while the allocation sites use
get_free_pages(). This causes issues separately allocating ptdescs
from struct page.

These patches convert the allocation/free sites to use ptdescs. In
the short term, this helps enable Matthew's work to allocate frozen
pagetables[1]. And in the long term, this will help us cleanly split
ptdesc allocations from struct page.

[1] https://lore.kernel.org/linux-mm/20251113140448.1814860-1-willy@infradead.org/
[2] https://lore.kernel.org/linux-mm/20251020001652.2116669-1-willy@infradead.org/T/#u

------

I've also tested this on a tree that separately allocates ptdescs. That
didn't find any lingering alloc/free issues.

I've realized that the pgd_list should also be using ptdescs (for 32bit
in this file). This can be done in a different patchset since there's
other users of pgd_list that still need to be converted.

Based on current mm-new.

v2:
  - Use pagetable_alloc() in populate_pgd() - in patch 2
  - Rename subject line to specify 64-bit (i.e. 32-bit wasn't converted)
  - Added reference links to the projects mentioned in the cover letter

Vishal Moola (Oracle) (3):
  x86/mm/pat: Convert pte code to use ptdescs
  x86/mm/pat: Convert pmd code to use ptdescs
  x86/mm/pat: Convert split_large_page() to use ptdescs

 arch/x86/mm/pat/set_memory.c | 43 ++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 19 deletions(-)

-- 
2.52.0

[PATCH v2 1/3] x86/mm/pat: Convert pte code to use ptdescs

[Vishal Moola (Oracle)]

In order to separately allocate ptdescs from pages, we need all allocation
and free sites to use the appropriate functions. Convert these pte
allocation/free sites to use ptdescs.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
---
 arch/x86/mm/pat/set_memory.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 6c6eb486f7a6..2dcb565d8f9b 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1408,7 +1408,7 @@ static bool try_to_free_pte_page(pte_t *pte)
 		if (!pte_none(pte[i]))
 			return false;
 
-	free_page((unsigned long)pte);
+	pagetable_free(virt_to_ptdesc((void *)pte));
 	return true;
 }
 
@@ -1537,9 +1537,10 @@ static void unmap_pud_range(p4d_t *p4d, unsigned long start, unsigned long end)
 	 */
 }
 
-static int alloc_pte_page(pmd_t *pmd)
+static int alloc_pte_ptdesc(pmd_t *pmd)
 {
-	pte_t *pte = (pte_t *)get_zeroed_page(GFP_KERNEL);
+	pte_t *pte = (pte_t *) ptdesc_address(
+			pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0));
 	if (!pte)
 		return -1;
 
@@ -1600,7 +1601,7 @@ static long populate_pmd(struct cpa_data *cpa,
 		 */
 		pmd = pmd_offset(pud, start);
 		if (pmd_none(*pmd))
-			if (alloc_pte_page(pmd))
+			if (alloc_pte_ptdesc(pmd))
 				return -1;
 
 		populate_pte(cpa, start, pre_end, cur_pages, pmd, pgprot);
@@ -1641,7 +1642,7 @@ static long populate_pmd(struct cpa_data *cpa,
 	if (start < end) {
 		pmd = pmd_offset(pud, start);
 		if (pmd_none(*pmd))
-			if (alloc_pte_page(pmd))
+			if (alloc_pte_ptdesc(pmd))
 				return -1;
 
 		populate_pte(cpa, start, end, num_pages - cur_pages,
-- 
2.52.0

[PATCH v2 2/3] x86/mm/pat: Convert pmd code to use ptdescs

[Vishal Moola (Oracle)]

In order to separately allocate ptdescs from pages, we need all allocation
and free sites to use the appropriate functions. Convert these pmd
allocation/free sites to use ptdescs.

populate_pgd() also allocates pagetables that may later be freed by
try_to_free_pmd_page(), so allocate ptdescs there as well.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
---
 arch/x86/mm/pat/set_memory.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 2dcb565d8f9b..ee3d0067aeea 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1420,7 +1420,7 @@ static bool try_to_free_pmd_page(pmd_t *pmd)
 		if (!pmd_none(pmd[i]))
 			return false;
 
-	free_page((unsigned long)pmd);
+	pagetable_free(virt_to_ptdesc((void *)pmd));
 	return true;
 }
 
@@ -1548,9 +1548,10 @@ static int alloc_pte_ptdesc(pmd_t *pmd)
 	return 0;
 }
 
-static int alloc_pmd_page(pud_t *pud)
+static int alloc_pmd_ptdesc(pud_t *pud)
 {
-	pmd_t *pmd = (pmd_t *)get_zeroed_page(GFP_KERNEL);
+	pmd_t *pmd = (pmd_t *) ptdesc_address(
+			pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0));
 	if (!pmd)
 		return -1;
 
@@ -1623,7 +1624,7 @@ static long populate_pmd(struct cpa_data *cpa,
 		 * We cannot use a 1G page so allocate a PMD page if needed.
 		 */
 		if (pud_none(*pud))
-			if (alloc_pmd_page(pud))
+			if (alloc_pmd_ptdesc(pud))
 				return -1;
 
 		pmd = pmd_offset(pud, start);
@@ -1679,7 +1680,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, p4d_t *p4d,
 		 * Need a PMD page?
 		 */
 		if (pud_none(*pud))
-			if (alloc_pmd_page(pud))
+			if (alloc_pmd_ptdesc(pud))
 				return -1;
 
 		cur_pages = populate_pmd(cpa, start, pre_end, cur_pages,
@@ -1716,7 +1717,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, p4d_t *p4d,
 
 		pud = pud_offset(p4d, start);
 		if (pud_none(*pud))
-			if (alloc_pmd_page(pud))
+			if (alloc_pmd_ptdesc(pud))
 				return -1;
 
 		tmp = populate_pmd(cpa, start, end, cpa->numpages - cur_pages,
@@ -1744,7 +1745,8 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
 	pgd_entry = cpa->pgd + pgd_index(addr);
 
 	if (pgd_none(*pgd_entry)) {
-		p4d = (p4d_t *)get_zeroed_page(GFP_KERNEL);
+		p4d = (p4d_t *) ptdesc_address(
+				pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0));
 		if (!p4d)
 			return -1;
 
@@ -1756,7 +1758,8 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
 	 */
 	p4d = p4d_offset(pgd_entry, addr);
 	if (p4d_none(*p4d)) {
-		pud = (pud_t *)get_zeroed_page(GFP_KERNEL);
+		pud = (pud_t *) ptdesc_address(
+				pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0));
 		if (!pud)
 			return -1;
 
-- 
2.52.0

[PATCH v2 3/3] x86/mm/pat: Convert split_large_page() to use ptdescs

[Vishal Moola (Oracle)]

In order to separately allocate ptdescs from pages, we need all allocation
and free sites to use the appropriate functions.

split_large_page() allocates a page to be used as a page table. This
should be allocating a ptdesc, so convert it.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
---
 arch/x86/mm/pat/set_memory.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index ee3d0067aeea..90ddd064c8c0 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1119,9 +1119,10 @@ static void split_set_pte(struct cpa_data *cpa, pte_t *pte, unsigned long pfn,
 
 static int
 __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
-		   struct page *base)
+		   struct ptdesc *ptdesc)
 {
 	unsigned long lpaddr, lpinc, ref_pfn, pfn, pfninc = 1;
+	struct page *base = ptdesc_page(ptdesc);
 	pte_t *pbase = (pte_t *)page_address(base);
 	unsigned int i, level;
 	pgprot_t ref_prot;
@@ -1226,18 +1227,18 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 static int split_large_page(struct cpa_data *cpa, pte_t *kpte,
 			    unsigned long address)
 {
-	struct page *base;
+	struct ptdesc *ptdesc;
 
 	if (!debug_pagealloc_enabled())
 		spin_unlock(&cpa_lock);
-	base = alloc_pages(GFP_KERNEL, 0);
+	ptdesc = pagetable_alloc(GFP_KERNEL, 0);
 	if (!debug_pagealloc_enabled())
 		spin_lock(&cpa_lock);
-	if (!base)
+	if (!ptdesc)
 		return -ENOMEM;
 
-	if (__split_large_page(cpa, kpte, address, base))
-		__free_page(base);
+	if (__split_large_page(cpa, kpte, address, ptdesc))
+		pagetable_free(ptdesc);
 
 	return 0;
 }
-- 
2.52.0

Re: [PATCH v2 0/3] Convert 64-bit x86/mm/pat to ptdescs

[Mike Rapoport]

Hi Vishal,

On Wed, Jan 28, 2026 at 02:40:46PM -0800, Vishal Moola (Oracle) wrote:
> x86/mm/pat should be using ptdescs. One line has already been
> converted to pagetable_free(), while the allocation sites use
> get_free_pages(). This causes issues separately allocating ptdescs
> from struct page.
> 
> These patches convert the allocation/free sites to use ptdescs. In
> the short term, this helps enable Matthew's work to allocate frozen
> pagetables[1]. And in the long term, this will help us cleanly split
> ptdesc allocations from struct page.
> 
> [1] https://lore.kernel.org/linux-mm/20251113140448.1814860-1-willy@infradead.org/
> [2] https://lore.kernel.org/linux-mm/20251020001652.2116669-1-willy@infradead.org/T/#u
> 
> ------
> 
> I've also tested this on a tree that separately allocates ptdescs. That
> didn't find any lingering alloc/free issues.
> 
> I've realized that the pgd_list should also be using ptdescs (for 32bit
> in this file). This can be done in a different patchset since there's
> other users of pgd_list that still need to be converted.

Since Andrew merges cover-letter text into the first commit changelog, some
explanation about pgd_list should be a part of that combined changelog.
 
> Based on current mm-new.
> 
> v2:
>   - Use pagetable_alloc() in populate_pgd() - in patch 2
>   - Rename subject line to specify 64-bit (i.e. 32-bit wasn't converted)
>   - Added reference links to the projects mentioned in the cover letter
> 
> Vishal Moola (Oracle) (3):
>   x86/mm/pat: Convert pte code to use ptdescs
>   x86/mm/pat: Convert pmd code to use ptdescs
>   x86/mm/pat: Convert split_large_page() to use ptdescs
> 
>  arch/x86/mm/pat/set_memory.c | 43 ++++++++++++++++++++----------------
>  1 file changed, 24 insertions(+), 19 deletions(-)
> 
> -- 
> 2.52.0
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH v2 1/3] x86/mm/pat: Convert pte code to use ptdescs

[Mike Rapoport]

On Wed, Jan 28, 2026 at 02:40:47PM -0800, Vishal Moola (Oracle) wrote:
> In order to separately allocate ptdescs from pages, we need all allocation
> and free sites to use the appropriate functions. Convert these pte
> allocation/free sites to use ptdescs.
> 
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
> ---
>  arch/x86/mm/pat/set_memory.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 6c6eb486f7a6..2dcb565d8f9b 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -1408,7 +1408,7 @@ static bool try_to_free_pte_page(pte_t *pte)
>  		if (!pte_none(pte[i]))
>  			return false;
>  
> -	free_page((unsigned long)pte);
> +	pagetable_free(virt_to_ptdesc((void *)pte));
>  	return true;
>  }
>  
> @@ -1537,9 +1537,10 @@ static void unmap_pud_range(p4d_t *p4d, unsigned long start, unsigned long end)
>  	 */
>  }
>  
> -static int alloc_pte_page(pmd_t *pmd)
> +static int alloc_pte_ptdesc(pmd_t *pmd)
>  {
> -	pte_t *pte = (pte_t *)get_zeroed_page(GFP_KERNEL);
> +	pte_t *pte = (pte_t *) ptdesc_address(
> +			pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0));

Sorry I missed this last time, but ptdesc_address(NULL) does not return
NULL. 
The allocation and conversion should be split IMHO.

This applies to all instances in all the patches.

>  	if (!pte)
>  		return -1;
>  
> @@ -1600,7 +1601,7 @@ static long populate_pmd(struct cpa_data *cpa,
>  		 */
>  		pmd = pmd_offset(pud, start);
>  		if (pmd_none(*pmd))
> -			if (alloc_pte_page(pmd))
> +			if (alloc_pte_ptdesc(pmd))
>  				return -1;
>  
>  		populate_pte(cpa, start, pre_end, cur_pages, pmd, pgprot);
> @@ -1641,7 +1642,7 @@ static long populate_pmd(struct cpa_data *cpa,
>  	if (start < end) {
>  		pmd = pmd_offset(pud, start);
>  		if (pmd_none(*pmd))
> -			if (alloc_pte_page(pmd))
> +			if (alloc_pte_ptdesc(pmd))
>  				return -1;
>  
>  		populate_pte(cpa, start, end, num_pages - cur_pages,
> -- 
> 2.52.0
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH v2 1/3] x86/mm/pat: Convert pte code to use ptdescs

[Vishal Moola (Oracle)]

On Thu, Jan 29, 2026 at 10:08:33AM +0200, Mike Rapoport wrote:
> On Wed, Jan 28, 2026 at 02:40:47PM -0800, Vishal Moola (Oracle) wrote:
> > In order to separately allocate ptdescs from pages, we need all allocation
> > and free sites to use the appropriate functions. Convert these pte
> > allocation/free sites to use ptdescs.
> > 
> > Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
> > ---
> >  arch/x86/mm/pat/set_memory.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> > index 6c6eb486f7a6..2dcb565d8f9b 100644
> > --- a/arch/x86/mm/pat/set_memory.c
> > +++ b/arch/x86/mm/pat/set_memory.c
> > @@ -1408,7 +1408,7 @@ static bool try_to_free_pte_page(pte_t *pte)
> >  		if (!pte_none(pte[i]))
> >  			return false;
> >  
> > -	free_page((unsigned long)pte);
> > +	pagetable_free(virt_to_ptdesc((void *)pte));
> >  	return true;
> >  }
> >  
> > @@ -1537,9 +1537,10 @@ static void unmap_pud_range(p4d_t *p4d, unsigned long start, unsigned long end)
> >  	 */
> >  }
> >  
> > -static int alloc_pte_page(pmd_t *pmd)
> > +static int alloc_pte_ptdesc(pmd_t *pmd)
> >  {
> > -	pte_t *pte = (pte_t *)get_zeroed_page(GFP_KERNEL);
> > +	pte_t *pte = (pte_t *) ptdesc_address(
> > +			pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0));
> 
> Sorry I missed this last time, but ptdesc_address(NULL) does not return
> NULL. 
> The allocation and conversion should be split IMHO.

Good catch.

> This applies to all instances in all the patches.

Thanks for reviewing, I'll send v3 with your feedback included next
week.

> >  	if (!pte)
> >  		return -1;
> >  
> > @@ -1600,7 +1601,7 @@ static long populate_pmd(struct cpa_data *cpa,
> >  		 */
> >  		pmd = pmd_offset(pud, start);
> >  		if (pmd_none(*pmd))
> > -			if (alloc_pte_page(pmd))
> > +			if (alloc_pte_ptdesc(pmd))
> >  				return -1;
> >  
> >  		populate_pte(cpa, start, pre_end, cur_pages, pmd, pgprot);
> > @@ -1641,7 +1642,7 @@ static long populate_pmd(struct cpa_data *cpa,
> >  	if (start < end) {
> >  		pmd = pmd_offset(pud, start);
> >  		if (pmd_none(*pmd))
> > -			if (alloc_pte_page(pmd))
> > +			if (alloc_pte_ptdesc(pmd))
> >  				return -1;
> >  
> >  		populate_pte(cpa, start, end, num_pages - cur_pages,
> > -- 
> > 2.52.0
> > 
> 
> -- 
> Sincerely yours,
> Mike.