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

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Message-ID: <aXsVgUHCnnvxtanV@kernel.org>
Date: Thu, 29 Jan 2026 10:08:33 +0200
From: Mike Rapoport <rppt@...nel.org>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	akpm@...ux-foundation.org,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 1/3] x86/mm/pat: Convert pte code to use ptdescs

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@...il.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.