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 1172C4052B1 for ; Tue, 11 Aug 2026 16:47:49 +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=1786466871; cv=none; b=sXbxKF4K9Y3ykYHl4ftVhtieoQwqrt8+1dIOyYctZ3mZsPLsjxdKEOHgeo2rGFfBxBDIiGx34SvAl8R+JvmO++kAVkKPNLJX3loMGLg6UR8iLviTljJxW4HlThlS0pmZwd77d3j7x6WK0LDCatRzAJ2+FxZVmbmLOXZ9l6El3Bk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786466871; c=relaxed/simple; bh=k6fuvdQDvEP8Vgz2PTv5lXUtwGGjwj2b08wkJAsWaVA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qW1FYA0keoy4q9biUuHww2LSoKk6cXRLEoLC2e7s7BzMp21dm4Bn1dvpALAixwX3IFI1b/id/CHiFBz7spYL6zND+60UOee2THlbbGcV+kzxugFIwA0xMdqcFBjUHbPZTryLnuyOv3XbJs2AccokubjB2Tjf+lLyjDR6EV68MpU= 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; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=gTV/2I8H; 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="gTV/2I8H" 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 392871516; Tue, 11 Aug 2026 09:47:45 -0700 (PDT) Received: from [10.57.5.246] (unknown [10.57.5.246]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CAF723F86F; Tue, 11 Aug 2026 09:47:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1786466869; bh=k6fuvdQDvEP8Vgz2PTv5lXUtwGGjwj2b08wkJAsWaVA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gTV/2I8He3BRcDFubFelv3SAtZiIJOlWDCGYb/PqwlMmSJRZUV+SfPlIf2y0trfly nKQsPwWsI+/aVoYR5dV3ihriAWJ5e9TgHciz8Ikf7zi44esgAkNV9YyJAGhPOgjzVd dWAjOsQ/MfHlSTn8IGEVVhT1EzNUwNUvSRhbFuk4= Message-ID: Date: Tue, 11 Aug 2026 18:47:36 +0200 Precedence: bulk X-Mailing-List: loongarch@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/22] mm: introduce MMF_KERNEL flag and set it for init_mm To: David Laight , "Christophe Leroy (CS GROUP)" Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Pasha Tatashin , Russell King , Catalin Marinas , Will Deacon , Ryan Roberts , linux-arm-kernel@lists.infradead.org, Huacai Chen , loongarch@lists.linux.dev, "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Gerald Schaefer , linux-s390@vger.kernel.org, "David S. Miller" , Andreas Larsson , sparclinux@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Ning Sun , x86@kernel.org, tboot-devel@lists.sourceforge.net, Ard Biesheuvel , Ilias Apalodimas , linux-efi@vger.kernel.org, Vishal Moola , Alistair Popple , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: <20260714-remove_pgtable_cdtor-v1-0-44be8a7685d7@arm.com> <20260714-remove_pgtable_cdtor-v1-3-44be8a7685d7@arm.com> <01f07ea2-8bdd-4450-8a49-548f8b646cfd@kernel.org> <20260811142507.4c6c760f@pumpkin> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260811142507.4c6c760f@pumpkin> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 11/08/2026 15:25, David Laight wrote: > On Mon, 3 Aug 2026 15:59:35 +0200 > "Christophe Leroy (CS GROUP)" wrote: > >> Le 14/07/2026 à 16:03, Kevin Brodsky a écrit : >>> mm code often needs to know whether some mm represents a kernel or >>> user address space. This is currently done by comparing the mm >>> pointer with &init_mm; besides not being particularly elegant, this >>> ignores the fact that other mm's (e.g. efi_mm) may also represent >>> parts of the kernel address space. >>> >>> Introduce a new mm flag MMF_KERNEL and set it for init_mm. >>> Subsequent patches will use this flag to replace comparisons with >>> &init_mm. No functional change is introduced for now. >> Did you consider performance impact ? This test is usually done in quite >> critical memory handling functions. >> >> init_mm is known at link time. Before your patch 08/22 there is just a >> comparison of mm (r3) with a constant (loaded in r10): >> >> c0014048 : >> c0014048: 3d 40 c1 09 lis r10,-16119 >> c001404c: 39 4a 03 98 addi r10,r10,920 >> c0014050: 7c 03 50 00 cmpw r3,r10 >> c0014054: 4d 82 00 20 beqlr >> ... >> >> After patch 08/22 we have, it first checks that mm is not 0, then it >> loads the word located at mm+528 then AND it with 0x1. This load might >> be costly. >> >> c0014048 : >> c0014048: 2c 03 00 00 cmpwi r3,0 >> c001404c: 7c 85 23 78 mr r5,r4 >> c0014050: 41 82 00 10 beq c0014060 >> c0014054: 81 23 02 10 lwz r9,528(r3) >> c0014058: 71 29 00 01 andi. r9,r9,1 >> c001405c: 4c 82 00 20 bnelr >> ... > Thought... > Could the check be replaced by one that checks for kernel static data? > That would require that other mm that represent part of the kernel > address space be static (and probably not in modules). > ISTR there is an address range check that can be used - and might be > cheaper than the explicit test for init_mm on many 64bit archs. That is actually an interesting idea. Finding those "kernel mms" boils down to looking for global mm_struct, so checking if mm points to global data would achieve essentially the same thing without a flag (and likely faster). I'm not sure we want to bake in the assumption that "kernel mm" is equivalent to "mm is global" though. - Kevin From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D4D6BC5B56A for ; Tue, 11 Aug 2026 16:48:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=24d7F6RqIX+xQnS4TfwFhcZngN5ZdljH4P4qE7KOtSM=; b=VP9v9JrAX0Ci65 I3EKZj91fHv88grMSPVeD6uS98q2BcS07tMG4BAGb8rFQxCG/EFfA7vDbsrooAuY/AnyV0KA8qiut d3lAR4BaL3rpeCTr+LakVRKd52f5QVj+PedTRwr72rEUAGTCrHw/5WPDFYDxFXpHqKThucQry1qbA pjgUskGgjk2rlRddB7dI0X5SrXq0FKrPDO2BS8/3RQPBdnBcdFD0jgnB7CNwnlDWFSA3a62n60h65 HzoXHF0FzqaQZQ9bd3zlruz+ue+N2TKSQqdRqr2NfM39eDpW3ra4URLWJVoFl2D/y3HNSFFuxzZJ/ Kh2exxghQnwrTqJkQovA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wtpds-0000000EY6p-3Lfg; Tue, 11 Aug 2026 16:47:56 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wtpdp-0000000EY5Q-14Dt; Tue, 11 Aug 2026 16:47:54 +0000 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 392871516; Tue, 11 Aug 2026 09:47:45 -0700 (PDT) Received: from [10.57.5.246] (unknown [10.57.5.246]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CAF723F86F; Tue, 11 Aug 2026 09:47:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1786466869; bh=k6fuvdQDvEP8Vgz2PTv5lXUtwGGjwj2b08wkJAsWaVA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gTV/2I8He3BRcDFubFelv3SAtZiIJOlWDCGYb/PqwlMmSJRZUV+SfPlIf2y0trfly nKQsPwWsI+/aVoYR5dV3ihriAWJ5e9TgHciz8Ikf7zi44esgAkNV9YyJAGhPOgjzVd dWAjOsQ/MfHlSTn8IGEVVhT1EzNUwNUvSRhbFuk4= Message-ID: Date: Tue, 11 Aug 2026 18:47:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/22] mm: introduce MMF_KERNEL flag and set it for init_mm To: David Laight , "Christophe Leroy (CS GROUP)" Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Pasha Tatashin , Russell King , Catalin Marinas , Will Deacon , Ryan Roberts , linux-arm-kernel@lists.infradead.org, Huacai Chen , loongarch@lists.linux.dev, "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Gerald Schaefer , linux-s390@vger.kernel.org, "David S. Miller" , Andreas Larsson , sparclinux@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Ning Sun , x86@kernel.org, tboot-devel@lists.sourceforge.net, Ard Biesheuvel , Ilias Apalodimas , linux-efi@vger.kernel.org, Vishal Moola , Alistair Popple , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: <20260714-remove_pgtable_cdtor-v1-0-44be8a7685d7@arm.com> <20260714-remove_pgtable_cdtor-v1-3-44be8a7685d7@arm.com> <01f07ea2-8bdd-4450-8a49-548f8b646cfd@kernel.org> <20260811142507.4c6c760f@pumpkin> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260811142507.4c6c760f@pumpkin> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260811_094753_461604_BB9591B9 X-CRM114-Status: GOOD ( 17.13 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org T24gMTEvMDgvMjAyNiAxNToyNSwgRGF2aWQgTGFpZ2h0IHdyb3RlOgo+IE9uIE1vbiwgMyBBdWcg MjAyNiAxNTo1OTozNSArMDIwMAo+ICJDaHJpc3RvcGhlIExlcm95IChDUyBHUk9VUCkiIDxjaGxl cm95QGtlcm5lbC5vcmc+IHdyb3RlOgo+Cj4+IExlIDE0LzA3LzIwMjYgw6AgMTY6MDMsIEtldmlu IEJyb2Rza3kgYSDDqWNyaXTCoDoKPj4+IG1tIGNvZGUgb2Z0ZW4gbmVlZHMgdG8ga25vdyB3aGV0 aGVyIHNvbWUgbW0gcmVwcmVzZW50cyBhIGtlcm5lbCBvcgo+Pj4gdXNlciBhZGRyZXNzIHNwYWNl LiBUaGlzIGlzIGN1cnJlbnRseSBkb25lIGJ5IGNvbXBhcmluZyB0aGUgbW0KPj4+IHBvaW50ZXIg d2l0aCAmaW5pdF9tbTsgYmVzaWRlcyBub3QgYmVpbmcgcGFydGljdWxhcmx5IGVsZWdhbnQsIHRo aXMKPj4+IGlnbm9yZXMgdGhlIGZhY3QgdGhhdCBvdGhlciBtbSdzIChlLmcuIGVmaV9tbSkgbWF5 IGFsc28gcmVwcmVzZW50Cj4+PiBwYXJ0cyBvZiB0aGUga2VybmVsIGFkZHJlc3Mgc3BhY2UuCj4+ Pgo+Pj4gSW50cm9kdWNlIGEgbmV3IG1tIGZsYWcgTU1GX0tFUk5FTCBhbmQgc2V0IGl0IGZvciBp bml0X21tLgo+Pj4gU3Vic2VxdWVudCBwYXRjaGVzIHdpbGwgdXNlIHRoaXMgZmxhZyB0byByZXBs YWNlIGNvbXBhcmlzb25zIHdpdGgKPj4+ICZpbml0X21tLiBObyBmdW5jdGlvbmFsIGNoYW5nZSBp cyBpbnRyb2R1Y2VkIGZvciBub3cuICAKPj4gRGlkIHlvdSBjb25zaWRlciBwZXJmb3JtYW5jZSBp bXBhY3QgPyBUaGlzIHRlc3QgaXMgdXN1YWxseSBkb25lIGluIHF1aXRlIAo+PiBjcml0aWNhbCBt ZW1vcnkgaGFuZGxpbmcgZnVuY3Rpb25zLgo+Pgo+PiBpbml0X21tIGlzIGtub3duIGF0IGxpbmsg dGltZS4gQmVmb3JlIHlvdXIgcGF0Y2ggMDgvMjIgdGhlcmUgaXMganVzdCBhIAo+PiBjb21wYXJp c29uIG9mIG1tIChyMykgd2l0aCBhIGNvbnN0YW50IChsb2FkZWQgaW4gcjEwKToKPj4KPj4gYzAw MTQwNDggPGFzc2VydF9wdGVfbG9ja2VkPjoKPj4gYzAwMTQwNDg6CTNkIDQwIGMxIDA5IAlsaXMg ICAgIHIxMCwtMTYxMTkKPj4gYzAwMTQwNGM6CTM5IDRhIDAzIDk4IAlhZGRpICAgIHIxMCxyMTAs OTIwCj4+IGMwMDE0MDUwOgk3YyAwMyA1MCAwMCAJY21wdyAgICByMyxyMTAKPj4gYzAwMTQwNTQ6 CTRkIDgyIDAwIDIwIAliZXFscgo+PiAuLi4KPj4KPj4gQWZ0ZXIgcGF0Y2ggMDgvMjIgd2UgaGF2 ZSwgaXQgZmlyc3QgY2hlY2tzIHRoYXQgbW0gaXMgbm90IDAsIHRoZW4gaXQgCj4+IGxvYWRzIHRo ZSB3b3JkIGxvY2F0ZWQgYXQgbW0rNTI4IHRoZW4gQU5EIGl0IHdpdGggMHgxLiBUaGlzIGxvYWQg bWlnaHQgCj4+IGJlIGNvc3RseS4KPj4KPj4gYzAwMTQwNDggPGFzc2VydF9wdGVfbG9ja2VkPjoK Pj4gYzAwMTQwNDg6CTJjIDAzIDAwIDAwIAljbXB3aSAgIHIzLDAKPj4gYzAwMTQwNGM6CTdjIDg1 IDIzIDc4IAltciAgICAgIHI1LHI0Cj4+IGMwMDE0MDUwOgk0MSA4MiAwMCAxMCAJYmVxICAgICBj MDAxNDA2MCA8YXNzZXJ0X3B0ZV9sb2NrZWQrMHgxOD4KPj4gYzAwMTQwNTQ6CTgxIDIzIDAyIDEw IAlsd3ogICAgIHI5LDUyOChyMykKPj4gYzAwMTQwNTg6CTcxIDI5IDAwIDAxIAlhbmRpLiAgIHI5 LHI5LDEKPj4gYzAwMTQwNWM6CTRjIDgyIDAwIDIwIAlibmVscgo+PiAuLi4KPiBUaG91Z2h0Li4u Cj4gQ291bGQgdGhlIGNoZWNrIGJlIHJlcGxhY2VkIGJ5IG9uZSB0aGF0IGNoZWNrcyBmb3Iga2Vy bmVsIHN0YXRpYyBkYXRhPwo+IFRoYXQgd291bGQgcmVxdWlyZSB0aGF0IG90aGVyIG1tIHRoYXQg cmVwcmVzZW50IHBhcnQgb2YgdGhlIGtlcm5lbAo+IGFkZHJlc3Mgc3BhY2UgYmUgc3RhdGljIChh bmQgcHJvYmFibHkgbm90IGluIG1vZHVsZXMpLgo+IElTVFIgdGhlcmUgaXMgYW4gYWRkcmVzcyBy YW5nZSBjaGVjayB0aGF0IGNhbiBiZSB1c2VkIC0gYW5kIG1pZ2h0IGJlCj4gY2hlYXBlciB0aGFu IHRoZSBleHBsaWNpdCB0ZXN0IGZvciBpbml0X21tIG9uIG1hbnkgNjRiaXQgYXJjaHMuCgpUaGF0 IGlzIGFjdHVhbGx5IGFuIGludGVyZXN0aW5nIGlkZWEuIEZpbmRpbmcgdGhvc2UgImtlcm5lbCBt bXMiIGJvaWxzCmRvd24gdG8gbG9va2luZyBmb3IgZ2xvYmFsIG1tX3N0cnVjdCwgc28gY2hlY2tp bmcgaWYgbW0gcG9pbnRzIHRvIGdsb2JhbApkYXRhIHdvdWxkIGFjaGlldmUgZXNzZW50aWFsbHkg dGhlIHNhbWUgdGhpbmcgd2l0aG91dCBhIGZsYWcgKGFuZCBsaWtlbHkKZmFzdGVyKS4gSSdtIG5v dCBzdXJlIHdlIHdhbnQgdG8gYmFrZSBpbiB0aGUgYXNzdW1wdGlvbiB0aGF0ICJrZXJuZWwgbW0i CmlzIGVxdWl2YWxlbnQgdG8gIm1tIGlzIGdsb2JhbCIgdGhvdWdoLgoKLSBLZXZpbgoKX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX18KbGludXgtcmlzY3YgbWFp bGluZyBsaXN0CmxpbnV4LXJpc2N2QGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0cDovL2xpc3RzLmlu ZnJhZGVhZC5vcmcvbWFpbG1hbi9saXN0aW5mby9saW51eC1yaXNjdgo=