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 CEEA01A4E70; Tue, 9 Sep 2025 09:05:54 +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=1757408757; cv=none; b=JtvpYCV5eTOmEyHuvsj0MVqP5eEPxvzg/MrteE4prSWhrW2riuoxyeYYoRWmZ6qbJaCQDNWrrhjhZ2shsw2KjZ5PLUIChZleA26v3cAkwlD++IEkBT40/JOziQtYpt3TzvxokCjdIp3LEw0NGUvW1Aa3ULCx+Zjh+YwNu2Cx4ow= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757408757; c=relaxed/simple; bh=PVcoYVsra2VVivjHJdr9TtHT2LeuybiCAVcVkV8gtlw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AesuKOx0XX08B418JmAAMDnZmKLXYseCwURUq2JbWVLP8G9gaN+O64LELqdysT/Hr8HBILfYJfzJc7/4WQmRWbP1ukXadq89mhgliKIU8WCwXM8a6aNtyvxaJhGRvb/egxjN5xHsCYzMjTsyisJ7kjRIOUpXhLsHpHvVJ78zrMY= 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 E25F015A1; Tue, 9 Sep 2025 02:05:44 -0700 (PDT) Received: from [10.57.60.124] (unknown [10.57.60.124]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A7EF13F63F; Tue, 9 Sep 2025 02:05:39 -0700 (PDT) Message-ID: Date: Tue, 9 Sep 2025 11:05:35 +0200 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: [PATCH v2 2/7] mm: introduce local state for lazy_mmu sections To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , David Hildenbrand , "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 References: <20250908073931.4159362-1-kevin.brodsky@arm.com> <20250908073931.4159362-3-kevin.brodsky@arm.com> <20250908224054.0a1969b493d8a837addd782e@linux-foundation.org> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: <20250908224054.0a1969b493d8a837addd782e@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 09/09/2025 07:40, Andrew Morton wrote: > On Mon, 8 Sep 2025 08:39:26 +0100 Kevin Brodsky wrote: > >> arch_{enter,leave}_lazy_mmu_mode() currently have a stateless API >> (taking and returning no value). This is proving problematic in >> situations where leave() needs to restore some context back to its >> original state (before enter() was called). In particular, this >> makes it difficult to support the nesting of lazy_mmu sections - >> leave() does not know whether the matching enter() call occurred >> while lazy_mmu was already enabled, and whether to disable it or >> not. >> >> This patch gives all architectures the chance to store local state >> while inside a lazy_mmu section by making enter() return some value, >> storing it in a local variable, and having leave() take that value. >> That value is typed lazy_mmu_state_t - each architecture defining >> __HAVE_ARCH_ENTER_LAZY_MMU_MODE is free to define it as it sees fit. >> For now we define it as int everywhere, which is sufficient to >> support nesting. >> >> The diff is unfortunately rather large as all the API changes need >> to be done atomically. Main parts: > This has a build error: > > CC arch/x86/kernel/asm-offsets.s > In file included from ./arch/x86/include/asm/irqflags.h:102, > from ./include/linux/irqflags.h:18, > from ./include/linux/spinlock.h:59, > from ./include/linux/swait.h:7, > from ./include/linux/completion.h:12, > from ./include/linux/crypto.h:15, > from arch/x86/kernel/asm-offsets.c:9: > ./arch/x86/include/asm/paravirt.h: In function 'arch_enter_lazy_mmu_mode': > ./arch/x86/include/asm/paravirt.h:534:16: error: 'LAZY_MMU_DEFAULT' undeclared (first use in this function) > 534 | return LAZY_MMU_DEFAULT; > | ^~~~~~~~~~~~~~~~ > ./arch/x86/include/asm/paravirt.h:534:16: note: each undeclared identifier is re > > which gets fixed up later in the series. Oh indeed good catch! I don't think there's an easy way to fix this cleanly due to the header soup. Since it's just a temporary change, I suggest: diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h index 65a0d394fba1..67b9549b4255 100644 --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -531,7 +531,7 @@ static inline lazy_mmu_state_t arch_enter_lazy_mmu_mode(void)  {      PVOP_VCALL0(mmu.lazy_mode.enter);   -    return LAZY_MMU_DEFAULT; +    return 0; /* LAZY_MMU_DEFAULT */  }    static inline void arch_leave_lazy_mmu_mode(lazy_mmu_state_t state) That will generate a trivial conflict with patch 4, naturally. Should I send a v3 with that change? - Kevin