linux-kernel - Re: [PATCH v5 1/8] mm: Add a ptdesc flag to mark kernel page tables

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Message-ID: <aObCAwbf1-Sxepni@casper.infradead.org>
Date: Wed, 8 Oct 2025 20:56:51 +0100
From: Matthew Wilcox <willy@...radead.org>
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>,
	iommu@...ts.linux.dev, security@...nel.org, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v5 1/8] mm: Add a ptdesc flag to mark kernel page tables

On Fri, Sep 19, 2025 at 01:39:59PM +0800, Lu Baolu wrote:
> +static inline void ptdesc_set_kernel(struct ptdesc *ptdesc)
> +{
> +	struct folio *folio = ptdesc_folio(ptdesc);
> +
> +	folio_set_referenced(folio);
> +}

So this was the right way to do this at the time.  However, if you look
at commit 522abd92279a this should now be ...

 enum pt_flags {
 	PT_reserved = PG_reserved,
+	PT_kernel = PG_referenced,
 	/* High bits are used for zone/node/section */
 };
[...]

+static inline void ptdesc_set_kernel(struct ptdesc *ptdesc)
+{
+	set_bit(PT_kernel, &pt->pt_flags.f);
+}

(etc)