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 F2E3FCA0FED for ; Wed, 10 Sep 2025 16:12:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type: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=cdS8DQ91Fk2KRig7JcdWAE1Tb1sePXx/4ByqYYrByXY=; b=fQ5mXzNHoNa5ljmpn99QxhuSvV lewUs46OwBf1VG6TarCsuS6Nnl9Rud6u6prD112eswdTQPTYxVAYAVjPsp5AacRQNAtgdarqALC4a rA3IYOFEwjcMRy2Wfan8SMN3lDrnfekpMskLBcVnIhm1tckc25UhD338Gst8pAgFxaDSJIBEVUJ43 9Aw9hL3w4h60Woiru4DL3kSTxdTlPIA+HJspi6grQlUDkf+/tWHlv0SUYmkZPEUDdexOsWWNGdL6j VSRitGqyphY9yuhFyQretgKj8TebC6WEkRso/23r/CKwxFufzLwqUVMc6IG54FsjYdkHyZfCg23bG XJCddGYQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwNQW-0000000FNuG-2Flf; Wed, 10 Sep 2025 16:12:08 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwNQT-0000000FNsl-1aOM for linux-arm-kernel@lists.infradead.org; Wed, 10 Sep 2025 16:12:07 +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 B91C716F2; Wed, 10 Sep 2025 09:11:55 -0700 (PDT) Received: from [10.57.67.148] (unknown [10.57.67.148]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8F3D43F63F; Wed, 10 Sep 2025 09:11:56 -0700 (PDT) Message-ID: <250835cd-f07a-4b8a-bc01-ace24b407efc@arm.com> Date: Wed, 10 Sep 2025 18:11:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/7] mm: introduce local state for lazy_mmu sections To: Alexander Gordeev Cc: David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , "David S. Miller" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Ryan Roberts , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, Mark Rutland References: <20250908073931.4159362-1-kevin.brodsky@arm.com> <20250908073931.4159362-3-kevin.brodsky@arm.com> <2fecfae7-1140-4a23-a352-9fd339fcbae5-agordeev@linux.ibm.com> <47ee1df7-1602-4200-af94-475f84ca8d80@arm.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250910_091205_539397_628F205F X-CRM114-Status: GOOD ( 18.74 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 09/09/2025 16:38, Alexander Gordeev wrote: >>>>> Would that integrate well with LAZY_MMU_DEFAULT etc? >>>> Hmm... I though the idea is to use LAZY_MMU_* by architectures that >>>> want to use it - at least that is how I read the description above. >>>> >>>> It is only kasan_populate|depopulate_vmalloc_pte() in generic code >>>> that do not follow this pattern, and it looks as a problem to me. >> This discussion also made me realise that this is problematic, as the >> LAZY_MMU_{DEFAULT,NESTED} macros were meant only for architectures' >> convenience, not for generic code (where lazy_mmu_state_t should ideally >> be an opaque type as mentioned above). It almost feels like the kasan >> case deserves a different API, because this is not how enter() and >> leave() are meant to be used. This would mean quite a bit of churn >> though, so maybe just introduce another arch-defined value to pass to >> leave() for such a situation - for instance, >> arch_leave_lazy_mmu_mode(LAZY_MMU_FLUSH)? > What about to adjust the semantics of apply_to_page_range() instead? > > It currently assumes any caller is fine with apply_to_pte_range() to > enter the lazy mode. By contrast, kasan_(de)populate_vmalloc_pte() are > not fine at all and must leave the lazy mode. That literally suggests > the original assumption is incorrect. > > We could change int apply_to_pte_range(..., bool create, ...) to e.g. > apply_to_pte_range(..., unsigned int flags, ...) and introduce a flag > that simply skips entering the lazy mmu mode. This is pretty much what Ryan proposed [1r] some time ago, although for a different purpose (avoiding nesting). There wasn't much appetite for it then, but I agree that this would be a more logical way to go about it. - Kevin [1r] https://lore.kernel.org/all/20250530140446.2387131-4-ryan.roberts@arm.com/