From nobody Thu Oct 2 09:19:20 2025 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DFFF426B96A for ; Fri, 19 Sep 2025 05:43:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.13 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758260589; cv=none; b=Noe6vULB/72C1fGxHalhn372DMSPgR4XLnXbP4T4tDR4PPg2KyU0B026AdC0VEIn6J29dPjEFmOLoOaC4KLopZfgE9HQI4VRtaMHzsKrCOsp4/ylahU0YfXXvGZqwQxP8grbqofkYRNp0W+tmBjk6Gt434y/plBNNVk9rC9GXvI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758260589; c=relaxed/simple; bh=XUszhuNZ389vB8JW9mMK3FCAh5uDSfA8sbiYQetS8U0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JtcXuz6fay1KvvmcGZR5TVE6TRmVTPOh3anEfAuqyHnD3cyV+79in/7JjIbaRm0DFezrwWMWdmBZS1vNer887mBPC2kyxS/XTxnYz8rjIDMlU7RyMcpMGQ9oj2Vyuss5eSNL9hxxfN6KJwkwaWF5K2LBsW4rAzLZiKQov/wxuDI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=ZEIF1OsF; arc=none smtp.client-ip=192.198.163.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="ZEIF1OsF" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1758260588; x=1789796588; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=XUszhuNZ389vB8JW9mMK3FCAh5uDSfA8sbiYQetS8U0=; b=ZEIF1OsFtQdFiuX9PDBXFdWVpOKW31yi8UaqowLiPrXuuRk0O2EnKwSN BXw8Rd/oMAk4D0Q6ak8n6ssnUK7m7YQ9cTi46jDXM6UDtXJDzRLDFR2e/ xSxFq43Ai5Lt1d0+WsnGzu3x7vPwD+y3SGrTynn9XnJ1QOrunl3kR2tVj xm6GoXlwkA4b11dkIJIFmsKnnalmZGa8QZAbmDDPyC60kZguNkV4xT4M6 a7hUQpf30eySkW0RPRm43II+pdwqK/jSrOJbFs/8jEA18RzQkWThp3rJz 4AbpOMt+gfTnwHAB2iHu9tK/2PohjpZX4Sb/xkJVQcEp3aYYHGXm1w0jL g==; X-CSE-ConnectionGUID: bIRhlVJDSG6Wy5qvIL3hlg== X-CSE-MsgGUID: axMiEAZqTH2o0QT0ZZQBmg== X-IronPort-AV: E=McAfee;i="6800,10657,11557"; a="63235837" X-IronPort-AV: E=Sophos;i="6.18,277,1751266800"; d="scan'208";a="63235837" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by fmvoesa107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Sep 2025 22:43:08 -0700 X-CSE-ConnectionGUID: bQxzzAHVRQKGYHmNzIp8gA== X-CSE-MsgGUID: DXTduhSRRmiv7fQx7EjT8A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.18,277,1751266800"; d="scan'208";a="180858756" Received: from allen-box.sh.intel.com ([10.239.159.52]) by orviesa005.jf.intel.com with ESMTP; 18 Sep 2025 22:43:01 -0700 From: Lu Baolu To: 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 Cc: iommu@lists.linux.dev, security@kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen , Lu Baolu Subject: [PATCH v5 6/8] mm: Introduce deferred freeing for kernel page tables Date: Fri, 19 Sep 2025 13:40:04 +0800 Message-ID: <20250919054007.472493-7-baolu.lu@linux.intel.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250919054007.472493-1-baolu.lu@linux.intel.com> References: <20250919054007.472493-1-baolu.lu@linux.intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Dave Hansen This introduces a conditional asynchronous mechanism, enabled by CONFIG_ASYNC_PGTABLE_FREE. When enabled, this mechanism defers the freeing of pages that are used as page tables for kernel address mappings. These pages are now queued to a work struct instead of being freed immediately. This deferred freeing provides a safe context for a future patch to add an IOMMU-specific callback, which might be expensive on large-scale systems. This ensures the necessary IOMMU cache invalidation is performed before the page is finally returned to the page allocator outside of any critical, non-sleepable path. Signed-off-by: Dave Hansen Signed-off-by: Lu Baolu Reviewed-by: Jason Gunthorpe Reviewed-by: Kevin Tian --- include/linux/mm.h | 16 +++++++++++++--- mm/pgtable-generic.c | 37 +++++++++++++++++++++++++++++++++++++ 2 files changed, 50 insertions(+), 3 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 668d519edc0f..2d7b4af40442 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2891,6 +2891,14 @@ static inline void __pagetable_free(struct ptdesc *p= t) __free_pages(page, compound_order(page)); } =20 +#ifdef CONFIG_ASYNC_PGTABLE_FREE +void pagetable_free_kernel(struct ptdesc *pt); +#else +static inline void pagetable_free_kernel(struct ptdesc *pt) +{ + __pagetable_free(pt); +} +#endif /** * pagetable_free - Free pagetables * @pt: The page table descriptor @@ -2900,10 +2908,12 @@ static inline void __pagetable_free(struct ptdesc *= pt) */ static inline void pagetable_free(struct ptdesc *pt) { - if (ptdesc_test_kernel(pt)) + if (ptdesc_test_kernel(pt)) { ptdesc_clear_kernel(pt); - - __pagetable_free(pt); + pagetable_free_kernel(pt); + } else { + __pagetable_free(pt); + } } =20 #if defined(CONFIG_SPLIT_PTE_PTLOCKS) diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c index 567e2d084071..0279399d4910 100644 --- a/mm/pgtable-generic.c +++ b/mm/pgtable-generic.c @@ -406,3 +406,40 @@ pte_t *__pte_offset_map_lock(struct mm_struct *mm, pmd= _t *pmd, pte_unmap_unlock(pte, ptl); goto again; } + +#ifdef CONFIG_ASYNC_PGTABLE_FREE +static void kernel_pgtable_work_func(struct work_struct *work); + +static struct { + struct list_head list; + /* protect above ptdesc lists */ + spinlock_t lock; + struct work_struct work; +} kernel_pgtable_work =3D { + .list =3D LIST_HEAD_INIT(kernel_pgtable_work.list), + .lock =3D __SPIN_LOCK_UNLOCKED(kernel_pgtable_work.lock), + .work =3D __WORK_INITIALIZER(kernel_pgtable_work.work, kernel_pgtable_wor= k_func), +}; + +static void kernel_pgtable_work_func(struct work_struct *work) +{ + struct ptdesc *pt, *next; + LIST_HEAD(page_list); + + spin_lock(&kernel_pgtable_work.lock); + list_splice_tail_init(&kernel_pgtable_work.list, &page_list); + spin_unlock(&kernel_pgtable_work.lock); + + list_for_each_entry_safe(pt, next, &page_list, pt_list) + __pagetable_free(pt); +} + +void pagetable_free_kernel(struct ptdesc *pt) +{ + spin_lock(&kernel_pgtable_work.lock); + list_add(&pt->pt_list, &kernel_pgtable_work.list); + spin_unlock(&kernel_pgtable_work.lock); + + schedule_work(&kernel_pgtable_work.work); +} +#endif --=20 2.43.0