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

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Message-ID: <aXuTAtwpSD8IABp_@fedora>
Date: Thu, 29 Jan 2026 09:04:02 -0800
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: Mike Rapoport <rppt@...nel.org>
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 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@...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.

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.