[PATCH 0/3] Convert x86/mm/pat to ptdescs

[PATCH 0/3] Convert 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. And in the long term, this will help us cleanly split
ptdesc allocations from struct page.

------

Based on current mm-new.

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 | 37 +++++++++++++++++++-----------------
 1 file changed, 20 insertions(+), 17 deletions(-)

-- 
2.52.0

[PATCH 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 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.

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 2dcb565d8f9b..ded1ba11c68f 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,
-- 
2.52.0

[PATCH 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 ded1ba11c68f..246b9cd3d13d 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 0/3] Convert x86/mm/pat to ptdescs

[Mike Rapoport]

Hi Vishal,

On Mon, Jan 26, 2026 at 04:51:37PM -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. And in the long term, this will help us cleanly split
> ptdesc allocations from struct page.
> 
> ------
> 
> Based on current mm-new.
> 
> Vishal Moola (Oracle) (3):
>   x86/mm/pat: Convert pte code to use ptdescs
>   x86/mm/pat: Convert pmd code to use ptdescs

There are still get_zeroed_page() calls in populate_pgd(). I think they
also should be converted to pagetable_alloc().

Other than that LGTM.

>   x86/mm/pat: Convert split_large_page() to use ptdescs
> 
>  arch/x86/mm/pat/set_memory.c | 37 +++++++++++++++++++-----------------
>  1 file changed, 20 insertions(+), 17 deletions(-)
> 
> -- 
> 2.52.0
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH 0/3] Convert x86/mm/pat to ptdescs

[Vishal Moola (Oracle)]

On Wed, Jan 28, 2026 at 01:52:43PM +0200, Mike Rapoport wrote:
> Hi Vishal,
> 
> On Mon, Jan 26, 2026 at 04:51:37PM -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. And in the long term, this will help us cleanly split
> > ptdesc allocations from struct page.
> > 
> > ------
> > 
> > Based on current mm-new.
> > 
> > Vishal Moola (Oracle) (3):
> >   x86/mm/pat: Convert pte code to use ptdescs
> >   x86/mm/pat: Convert pmd code to use ptdescs
> 
> There are still get_zeroed_page() calls in populate_pgd(). I think they
> also should be converted to pagetable_alloc().

Thanks, I missed those. They should be converted too, so I'll add those
in v2.

> Other than that LGTM.
> 
> >   x86/mm/pat: Convert split_large_page() to use ptdescs
> > 
> >  arch/x86/mm/pat/set_memory.c | 37 +++++++++++++++++++-----------------
> >  1 file changed, 20 insertions(+), 17 deletions(-)
> > 
> > -- 
> > 2.52.0
> > 
> 
> -- 
> Sincerely yours,
> Mike.