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X-CSE-ConnectionGUID: Nqr2Hhl4QSKIFj4Lj7OHyw== X-CSE-MsgGUID: I/yGvG9kSfaUefEm8Ngf+g== X-IronPort-AV: E=McAfee;i="6800,10657,11578"; a="62258570" X-IronPort-AV: E=Sophos;i="6.19,220,1754982000"; d="scan'208";a="62258570" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by orvoesa111.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Oct 2025 23:28:20 -0700 X-CSE-ConnectionGUID: ak6XigH/QdeMlk+cNQCyDA== X-CSE-MsgGUID: +31j5JXqT2muzztIzmPLXQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,220,1754982000"; d="scan'208";a="180257706" Received: from allen-sbox.sh.intel.com (HELO [10.239.159.30]) ([10.239.159.30]) by orviesa006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Oct 2025 23:28:14 -0700 Message-ID: <3971a3fd-c733-4864-851a-87dc9d3f686a@linux.intel.com> Date: Sat, 11 Oct 2025 14:24:41 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 1/8] mm: Add a ptdesc flag to mark kernel page tables To: Matthew Wilcox Cc: Joerg Roedel , Will Deacon , Robin Murphy , Kevin Tian , Jason Gunthorpe , Jann Horn , Vasant Hegde , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Alistair Popple , Peter Zijlstra , Uladzislau Rezki , Jean-Philippe Brucker , Andy Lutomirski , Yi Lai , iommu@lists.linux.dev, security@kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen References: <20250919054007.472493-1-baolu.lu@linux.intel.com> <20250919054007.472493-2-baolu.lu@linux.intel.com> Content-Language: en-US From: Baolu Lu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 6C7CC100009 X-Stat-Signature: mhehj7uurppng5so1eoqy87ksmyfsnnh X-Rspam-User: X-HE-Tag: 1760164101-230741 X-HE-Meta: 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 pwqxrK0s KaGWXXiVOo6nms9FTQQcW3w3EXabnEu4yqMHDNTrmzEi/nZL992T2HTn2lLoYjWFEdGh5TlUduZ003mjLkHhRZWJNV+mMid4PQ3Uc/ObUIm1WDLNR2+ImThUY958JBKVrkpICxbi0pt/R0oTFwk12Tvwqj4awHXLdH90V4gSgIft6uoCvsZXnzlNaR4n6aMZFA6e2yg/HizfAlee1z6LcD5i5WUWyLZjyOeqPd2uu5oh8DcU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/9/25 03:56, Matthew Wilcox wrote: > 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); > +} Thank you for the review comment. I updated the patch like the following: diff --git a/include/linux/mm.h b/include/linux/mm.h index a3f97c551ad8..5abd427b6202 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2940,6 +2940,7 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a #endif /* CONFIG_MMU */ enum pt_flags { + PT_kernel = PG_referenced, PT_reserved = PG_reserved, /* High bits are used for zone/node/section */ }; @@ -2965,6 +2966,46 @@ static inline bool pagetable_is_reserved(struct ptdesc *pt) return test_bit(PT_reserved, &pt->pt_flags.f); } +/** + * ptdesc_set_kernel - Mark a ptdesc used to map the kernel + * @ptdesc: The ptdesc to be marked + * + * Kernel page tables often need special handling. Set a flag so that + * the handling code knows this ptdesc will not be used for userspace. + */ +static inline void ptdesc_set_kernel(struct ptdesc *ptdesc) +{ + set_bit(PT_kernel, &ptdesc->pt_flags.f); +} + +/** + * ptdesc_clear_kernel - Mark a ptdesc as no longer used to map the kernel + * @ptdesc: The ptdesc to be unmarked + * + * Use when the ptdesc is no longer used to map the kernel and no longer + * needs special handling. + */ +static inline void ptdesc_clear_kernel(struct ptdesc *ptdesc) +{ + /* + * Note: the 'PG_referenced' bit does not strictly need to be + * cleared before freeing the page. But this is nice for + * symmetry. + */ + clear_bit(PT_kernel, &ptdesc->pt_flags.f); +} + +/** + * ptdesc_test_kernel - Check if a ptdesc is used to map the kernel + * @ptdesc: The ptdesc being tested + * + * Call to tell if the ptdesc used to map the kernel. + */ +static inline bool ptdesc_test_kernel(struct ptdesc *ptdesc) +{ + return test_bit(PT_kernel, &ptdesc->pt_flags.f); +} + /** * pagetable_alloc - Allocate pagetables * @gfp: GFP flags Thanks, baolu