Re: [PATCH v3 1/3] x86/mm/pat: Convert pte code to use ptdescs

Mike Rapoport
2026-02-03T17:03:10Z

Hi Vishal,

On Mon, Feb 02, 2026 at 09:20:03AM -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 | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 6c6eb486f7a6..f9f9d4ca8e71 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;
> }
>
> @@ -1537,12 +1537,15 @@ 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);
> - if (!pte)
> + pte_t *pte;
> + struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0);

AFAIR, x86 folks like reverse xmas tree for variable declarations.

> +
> + if (!ptdesc)
> return -1;
>
> + pte = (pte_t *) ptdesc_address(ptdesc);

No need to cast void * to another pointer type.

Same comments are relevant for two other patches as well.

> set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
> return 0;
> }
> @@ -1600,7 +1603,7 @@ 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 +1644,7 @@ 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.