[PATCH v3 2/3] x86/mm/pat: Convert pmd code to use ptdescs

Vishal Moola (Oracle)
2026-02-02T17:20:24Z

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 | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index f9f9d4ca8e71..9f531c87531b 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;
}

@@ -1550,12 +1550,15 @@ 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);
- if (!pmd)
+ pmd_t *pmd;
+ struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0);
+
+ if (!ptdesc)
return -1;

+ pmd = (pmd_t *) ptdesc_address(ptdesc);
set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
return 0;
}
@@ -1625,7 +1628,7 @@ 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);
@@ -1681,7 +1684,7 @@ 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,
@@ -1718,7 +1721,7 @@ 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,
@@ -1742,14 +1745,16 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
p4d_t *p4d;
pgd_t *pgd_entry;
long ret;
+ struct ptdesc *ptdesc;

pgd_entry = cpa->pgd + pgd_index(addr);

if (pgd_none(*pgd_entry)) {
- p4d = (p4d_t *)get_zeroed_page(GFP_KERNEL);
- if (!p4d)
+ ptdesc = pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0);
+ if (!ptdesc)
return -1;

+ p4d = (p4d_t *) ptdesc_address(ptdesc);
set_pgd(pgd_entry, __pgd(__pa(p4d) | _KERNPG_TABLE));
}

@@ -1758,10 +1763,11 @@ 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);
- if (!pud)
+ ptdesc = pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0);
+ if (!ptdesc)
return -1;

+ pud = (pud_t *) ptdesc_address(ptdesc);
set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
}

--
2.52.0