From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 523E953363 for ; Mon, 3 Nov 2025 08:44:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762159447; cv=none; b=KkdlTnLhHqT5Cm1Q9mNs2zirFNqUWjrT+4EVg9EpyOMCJk8E+oXCZWPpJr4CivDDoLtV/p9AeByvj4iqF+6c0l/HHATNH4ZESCCl4BgKhsoUAyBF8A8CL5pXb1RXbAG+R6lERatOPMau6YGxxQUs8i9J8Tw0iPa3zqMEqDyc/Gw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762159447; c=relaxed/simple; bh=ErdmyhYmbu+Q9MnDZ2ZB5VBnhzRHqOJACZeTJaH+/b4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=RUfqDOQ5cOmNSKUy7U5lu0oBFevxzB/BBFhpHPGj1cj0FBlCrv/5xl4/yHC+DzsMauql8fRdioOP2wlgGT2MPsXWktbUf9z6YP+anLTaJsGF78RXWPrntIA99aP+L+42o5qyskLDTJv2aJbkStuXOZ6KmToYEiUzKBt2SZrRW1o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BF88A1D13; Mon, 3 Nov 2025 00:43:56 -0800 (PST) Received: from [10.164.136.41] (unknown [10.164.136.41]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3999F3F694; Mon, 3 Nov 2025 00:43:57 -0800 (PST) Message-ID: <666e012e-0b13-4def-82de-55ccd5868d36@arm.com> Date: Mon, 3 Nov 2025 14:13:55 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: Enable CONFIG_PT_RECLAIM on all architectures To: Qi Zheng , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, catalin.marinas@arm.com, will@kernel.org, akpm@linux-foundation.org, david@redhat.com, hannes@cmpxchg.org Cc: ryan.roberts@arm.com, hpa@zytor.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, ppt@kernel.org, surenb@google.com, mhocko@suse.com, shakeel.butt@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20251103063718.90743-1-dev.jain@arm.com> <044e3f9a-3de2-4939-afff-3bb527eb024b@bytedance.com> Content-Language: en-US From: Dev Jain In-Reply-To: <044e3f9a-3de2-4939-afff-3bb527eb024b@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 03/11/25 12:33 pm, Qi Zheng wrote: > Hi Dev, > > On 11/3/25 2:37 PM, Dev Jain wrote: >> The implementation of CONFIG_PT_RECLAIM is completely contained in >> generic >> mm code. It depends on the RCU callback which will reclaim the >> pagetables - >> there is nothing arch-specific about that. So, enable this config for >> all architectures. > > Thanks for doing this! > > But unfortunately, not all architectures call tlb_remove_ptdesc() in > __pte_free_tlb(). Some architectures directly call pte_free() to > free PTE pages (without RCU). Thanks! This was not obvious to figure out. Is there an arch bottleneck because of which they do this? I mean to say, is something stopping us from simply redirecting __pte_free_tlb to tlb_remove_ptdesc or pte_free_defer? I am looking to enable this config at least on arm64 by default, I believe it will be legal to do this at least here. > > We need to modify these architectures first, otherwise it will > lead to UAF. This approach is feasible because Hugh provides similar > support in pte_free_defer(). > > Enabling PT_RECLAIM on all architecture has always been on my > TODO list, but it's been blocked by other things. :( > > Thanks, > Qi > >> >> Signed-off-by: Dev Jain >> --- >>   arch/x86/Kconfig | 1 - >>   mm/Kconfig       | 5 +---- >>   mm/pt_reclaim.c  | 2 +- >>   3 files changed, 2 insertions(+), 6 deletions(-) >> >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >> index fa3b616af03a..5681308a5650 100644 >> --- a/arch/x86/Kconfig >> +++ b/arch/x86/Kconfig >> @@ -327,7 +327,6 @@ config X86 >>       select FUNCTION_ALIGNMENT_4B >>       imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI >>       select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE >> -    select ARCH_SUPPORTS_PT_RECLAIM        if X86_64 >>       select ARCH_SUPPORTS_SCHED_SMT        if SMP >>       select SCHED_SMT            if SMP >>       select ARCH_SUPPORTS_SCHED_CLUSTER    if SMP >> diff --git a/mm/Kconfig b/mm/Kconfig >> index 0e26f4fc8717..903c37d02555 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -1355,13 +1355,10 @@ config ARCH_HAS_USER_SHADOW_STACK >>         The architecture has hardware support for userspace shadow call >>             stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss). >>   -config ARCH_SUPPORTS_PT_RECLAIM >> -    def_bool n >> - >>   config PT_RECLAIM >>       bool "reclaim empty user page table pages" >>       default y >> -    depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP >> +    depends on MMU && SMP >>       select MMU_GATHER_RCU_TABLE_FREE >>       help >>         Try to reclaim empty user page table pages in paths other >> than munmap >> diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c >> index 7e9455a18aae..049e17f08c6a 100644 >> --- a/mm/pt_reclaim.c >> +++ b/mm/pt_reclaim.c >> @@ -1,6 +1,6 @@ >>   // SPDX-License-Identifier: GPL-2.0 >>   #include >> -#include >> +#include >>   #include >>     #include "internal.h" >