linux-kernel - Re: [PATCH v7 6/8] x86/mm: Use pagetable

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Message-ID: <aRvWfv_fc60zUK1d@fedora>
Date: Mon, 17 Nov 2025 18:14:22 -0800
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...dia.com>,
	Jann Horn <jannh@...gle.com>, Vasant Hegde <vasant.hegde@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...el.com>,
	Alistair Popple <apopple@...dia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Andy Lutomirski <luto@...nel.org>, Yi Lai <yi1.lai@...el.com>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Michal Hocko <mhocko@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Vinicius Costa Gomes <vinicius.gomes@...el.com>,
	iommu@...ts.linux.dev, security@...nel.org, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 6/8] x86/mm: Use pagetable_free()

On Wed, Oct 22, 2025 at 04:26:32PM +0800, Lu Baolu wrote:
> The kernel's memory management subsystem provides a dedicated interface,
> pagetable_free(), for freeing page table pages. Updates two call sites to
> use pagetable_free() instead of the lower-level __free_page() or
> free_pages(). This improves code consistency and clarity, and ensures the
> correct freeing mechanism is used.

In doing these ptdesc calls here, we're running into issues with the
concurrent work around ptdescs: Allocating frozen page tables[1] and
separately allocating ptdesc[2].

What we're seeing is attempts to cast a page that has still been
allocated by the regular page allocator to a ptdesc - which won't work
anymore.

My hunch is we want alot of the code in pat/set_memory.c to be using ptdescs
aka page table descriptors. At least all the allocations/frees for now.
Does that seem right? I'm not really familiar with this code though...

[1] https://lore.kernel.org/linux-mm/202511172257.ffd96dab-lkp@intel.com/T/#mf68f9c13f4b188eac08ae261c0172afe81a75827
[2] https://lore.kernel.org/linux-mm/20251020001652.2116669-1-willy@infradead.org/T/#md72f66473e017d6f3ce277405ad115e71898f418

> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> ---
>  arch/x86/mm/init_64.c        | 2 +-
>  arch/x86/mm/pat/set_memory.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 0e4270e20fad..3d9a5e4ccaa4 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1031,7 +1031,7 @@ static void __meminit free_pagetable(struct page *page, int order)
>  		free_reserved_pages(page, nr_pages);
>  #endif
>  	} else {
> -		__free_pages(page, order);
> +		pagetable_free(page_ptdesc(page));
>  	}
>  }
>  
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 970981893c9b..fffb6ef1997d 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -429,7 +429,7 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)
>  
>  	list_for_each_entry_safe(ptdesc, tmp, &pgtables, pt_list) {
>  		list_del(&ptdesc->pt_list);
> -		__free_page(ptdesc_page(ptdesc));
> +		pagetable_free(ptdesc);
>  	}
>  }
>  
> -- 
> 2.43.0
>