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 C61F91E515; Thu, 4 Dec 2025 04:34:17 +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=1764822860; cv=none; b=LL+fy4zY5CAz5mnFdOqXiKv32JwYaIgKhci7A31vOS9N/dVUUFXA6EYEgCoYFvmsu4axqtw2y4kXO76kp4kOcCX/EEWshUke+8ZeAEqCs+volPgDw7HgyI2R2ZNGzQQ/h4trA5Xf5kjVBCcE91Zxr/2FxiJON+p+jpF9KtOmBPY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764822860; c=relaxed/simple; bh=TWSO2r05d0Wp8yOH3Z+lta+FonomABUz77+wZWudcdo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WTo7vo/NJeKohSDwysX1kECgkxI3yguRM/5IMClhijSdtYrjmgwij+S6Fr4V+qtUzBZA9iLg+wx6C+RVjxc1M31Diqdk2rz/NTBkJAWMvVH4VWg3VomwQOCvF1AhuddrYB93EKo/LwDYSC6xH3THhg4iGn+mSviPmn0JhiW2PPg= 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 64906339; Wed, 3 Dec 2025 20:34:09 -0800 (PST) Received: from [10.164.18.78] (unknown [10.164.18.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E05AF3F73B; Wed, 3 Dec 2025 20:34:06 -0800 (PST) Message-ID: <565ac89c-1e7a-4e2f-a866-15039fbe22f6@arm.com> Date: Thu, 4 Dec 2025 10:04:04 +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: [PATCH v5 07/12] mm: bail out of lazy_mmu_mode_* in interrupt context To: Kevin Brodsky , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , David Hildenbrand , "David S. Miller" , David Woodhouse , "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 , "Ritesh Harjani (IBM)" , Ryan Roberts , Suren Baghdasaryan , Thomas Gleixner , Venkat Rao Bagalkote , 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, x86@kernel.org References: <20251124132228.622678-1-kevin.brodsky@arm.com> <20251124132228.622678-8-kevin.brodsky@arm.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <20251124132228.622678-8-kevin.brodsky@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 24/11/25 6:52 PM, Kevin Brodsky wrote: > The lazy MMU mode cannot be used in interrupt context. This is > documented in , but isn't consistently handled > across architectures. > > arm64 ensures that calls to lazy_mmu_mode_* have no effect in > interrupt context, because such calls do occur in certain > configurations - see commit b81c688426a9 ("arm64/mm: Disable barrier > batching in interrupt contexts"). Other architectures do not check > this situation, most likely because it hasn't occurred so far. > > Let's handle this in the new generic lazy_mmu layer, in the same > fashion as arm64: bail out of lazy_mmu_mode_* if in_interrupt(). > Also remove the arm64 handling that is now redundant. Ensuring a common behaviour across platforms such as this in interrupt context bail out - can now be easily achieved now as there are generic helpers that call the platform ones. > > Both arm64 and x86/Xen also ensure that any lazy MMU optimisation is > disabled while in interrupt (see queue_pte_barriers() and > xen_get_lazy_mode() respectively). This will be handled in the > generic layer in a subsequent patch. Makes sense. > > Signed-off-by: Kevin Brodsky > --- > arch/arm64/include/asm/pgtable.h | 9 --------- > include/linux/pgtable.h | 17 +++++++++++++++-- > 2 files changed, 15 insertions(+), 11 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 54f8d6bb6f22..e596899f4029 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -94,26 +94,17 @@ static inline void arch_enter_lazy_mmu_mode(void) > * keeps tracking simple. > */ > > - if (in_interrupt()) > - return; > - > set_thread_flag(TIF_LAZY_MMU); > } > > static inline void arch_flush_lazy_mmu_mode(void) > { > - if (in_interrupt()) > - return; > - > if (test_and_clear_thread_flag(TIF_LAZY_MMU_PENDING)) > emit_pte_barriers(); > } > > static inline void arch_leave_lazy_mmu_mode(void) > { > - if (in_interrupt()) > - return; > - > arch_flush_lazy_mmu_mode(); > clear_thread_flag(TIF_LAZY_MMU); > } > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index c121358dba15..8ff6fdb4b13d 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -228,27 +228,40 @@ static inline int pmd_dirty(pmd_t pmd) > * of the lazy mode. So the implementation must assume preemption may be enabled > * and cpu migration is possible; it must take steps to be robust against this. > * (In practice, for user PTE updates, the appropriate page table lock(s) are > - * held, but for kernel PTE updates, no lock is held). Nesting is not permitted > - * and the mode cannot be used in interrupt context. > + * held, but for kernel PTE updates, no lock is held). The mode is disabled in > + * interrupt context and calls to the lazy_mmu API have no effect. > + * Nesting is not permitted. Right - nesting is still not not permitted. > */> #ifdef CONFIG_ARCH_HAS_LAZY_MMU_MODE > static inline void lazy_mmu_mode_enable(void) > { > + if (in_interrupt()) > + return; > + > arch_enter_lazy_mmu_mode(); > } > > static inline void lazy_mmu_mode_disable(void) > { > + if (in_interrupt()) > + return; > + > arch_leave_lazy_mmu_mode(); > } > > static inline void lazy_mmu_mode_pause(void) > { > + if (in_interrupt()) > + return; > + > arch_leave_lazy_mmu_mode(); > } > > static inline void lazy_mmu_mode_resume(void) > { > + if (in_interrupt()) > + return; > + > arch_enter_lazy_mmu_mode(); > } > #else LGTM Reviewed-by: Anshuman Khandual