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 D3AFA17A2EF for ; Mon, 9 Jun 2025 11:01:33 +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=1749466896; cv=none; b=ntHnCeFR0UDIrluXrGuWf9Oc5SVU0Vuz63F0OTj2xwzG2/cljoKsyPeIISkjQDyF4mpPTsxPKhcP+pXwANyB5MGV3lpfhXPKib3Fbp2kYiALTWztCccHJ1XX0gmw4jTOtLun8q2tcA6zt6alxWYzZ+fNsR5zcEpyyDHkXWtCX28= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749466896; c=relaxed/simple; bh=sW/tuZS+zOkPGXhMcIMsU9CmOXZjhK5Sr/PFTnT/LY8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lLDHWgUV8CV4MlHMTnza0ePM2MlK8qbGMYtxLeoveI9JlAQu6hgGUuc1Mh1/Yz6YAhEDXsdlhwWzYWJBnqfjkPqZ1jGhJEpE1la3xRlpEJTAEudHIAm1kwIkc02pnY8kg8nxS1rJdf2QgMMZNn3R6Q9sf6fyo9VQMI5Ykon7ZsY= 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 F02C2150C; Mon, 9 Jun 2025 04:01:13 -0700 (PDT) Received: from [10.1.39.162] (XHFQ2J9959.cambridge.arm.com [10.1.39.162]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C82543F59E; Mon, 9 Jun 2025 04:01:29 -0700 (PDT) Message-ID: Date: Mon, 9 Jun 2025 12:01:28 +0100 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 v1] mm: Remove arch_flush_tlb_batched_pending() arch helper Content-Language: en-GB To: Lorenzo Stoakes Cc: Andrew Morton , Catalin Marinas , Will Deacon , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , David Hildenbrand , Rik van Riel , "Liam R. Howlett" , Vlastimil Babka , Harry Yoo , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-mm@kvack.org References: <20250609103132.447370-1-ryan.roberts@arm.com> <48375ad8-7461-446e-9002-8d326fba137b@lucifer.local> From: Ryan Roberts In-Reply-To: <48375ad8-7461-446e-9002-8d326fba137b@lucifer.local> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 09/06/2025 11:45, Lorenzo Stoakes wrote: > On Mon, Jun 09, 2025 at 11:31:30AM +0100, Ryan Roberts wrote: >> Since commit 4b634918384c ("arm64/mm: Close theoretical race where stale >> TLB entry remains valid"), all arches that use tlbbatch for reclaim >> (arm64, riscv, x86) implement arch_flush_tlb_batched_pending() with a >> flush_tlb_mm(). >> >> So let's simplify by removing the unnecessary abstraction and doing the >> flush_tlb_mm() directly in flush_tlb_batched_pending(). This effectively >> reverts commit db6c1f6f236d ("mm/tlbbatch: introduce >> arch_flush_tlb_batched_pending()"). >> >> Suggested-by: Will Deacon >> Signed-off-by: Ryan Roberts > > Thanks, love to see an arch_*() helper go :) > > Reviewed-by: Lorenzo Stoakes Thanks! > > Couple points below. > >> --- >> arch/arm64/include/asm/tlbflush.h | 11 ----------- >> arch/riscv/include/asm/tlbflush.h | 1 - >> arch/riscv/mm/tlbflush.c | 5 ----- >> arch/x86/include/asm/tlbflush.h | 5 ----- >> mm/rmap.c | 2 +- >> 5 files changed, 1 insertion(+), 23 deletions(-) >> >> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h >> index aa9efee17277..18a5dc0c9a54 100644 >> --- a/arch/arm64/include/asm/tlbflush.h >> +++ b/arch/arm64/include/asm/tlbflush.h >> @@ -322,17 +322,6 @@ static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm) >> return true; >> } >> >> -/* >> - * If mprotect/munmap/etc occurs during TLB batched flushing, we need to ensure >> - * all the previously issued TLBIs targeting mm have completed. But since we >> - * can be executing on a remote CPU, a DSB cannot guarantee this like it can >> - * for arch_tlbbatch_flush(). Our only option is to flush the entire mm. >> - */ > > Hm are we losing information here? I guess it's hard to know whewre to put > this though. The generic version of this comment exists above flush_tlb_batched_pending() in rmap.c. For the arm64-specific description of why we need to flush the whole mm, that's captured in Commit 4b634918384c ("arm64/mm: Close theoretical race where stale TLB entry remains valid"), although I accept that may not be the first place someone looks. I don't think we should be defining arch_ helpers just to provide a hook for some arch-specific comments though. > >> -static inline void arch_flush_tlb_batched_pending(struct mm_struct *mm) >> -{ >> - flush_tlb_mm(mm); >> -} >> - >> /* >> * To support TLB batched flush for multiple pages unmapping, we only send >> * the TLBI for each page in arch_tlbbatch_add_pending() and wait for the >> diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h >> index 1a20dd746a49..eed0abc40514 100644 >> --- a/arch/riscv/include/asm/tlbflush.h >> +++ b/arch/riscv/include/asm/tlbflush.h >> @@ -63,7 +63,6 @@ void flush_pud_tlb_range(struct vm_area_struct *vma, unsigned long start, >> bool arch_tlbbatch_should_defer(struct mm_struct *mm); >> void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch, >> struct mm_struct *mm, unsigned long start, unsigned long end); >> -void arch_flush_tlb_batched_pending(struct mm_struct *mm); >> void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch); >> >> extern unsigned long tlb_flush_all_threshold; >> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c >> index e737ba7949b1..8404530ec00f 100644 >> --- a/arch/riscv/mm/tlbflush.c >> +++ b/arch/riscv/mm/tlbflush.c >> @@ -234,11 +234,6 @@ void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch, >> mmu_notifier_arch_invalidate_secondary_tlbs(mm, start, end); >> } >> >> -void arch_flush_tlb_batched_pending(struct mm_struct *mm) >> -{ >> - flush_tlb_mm(mm); >> -} >> - >> void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) >> { >> __flush_tlb_range(NULL, &batch->cpumask, >> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h >> index e9b81876ebe4..00daedfefc1b 100644 >> --- a/arch/x86/include/asm/tlbflush.h >> +++ b/arch/x86/include/asm/tlbflush.h >> @@ -356,11 +356,6 @@ static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *b >> mmu_notifier_arch_invalidate_secondary_tlbs(mm, 0, -1UL); >> } >> >> -static inline void arch_flush_tlb_batched_pending(struct mm_struct *mm) >> -{ >> - flush_tlb_mm(mm); >> -} >> - >> extern void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch); >> >> static inline bool pte_flags_need_flush(unsigned long oldflags, >> diff --git a/mm/rmap.c b/mm/rmap.c >> index fb63d9256f09..fd160ddaa980 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -746,7 +746,7 @@ void flush_tlb_batched_pending(struct mm_struct *mm) >> int flushed = batch >> TLB_FLUSH_BATCH_FLUSHED_SHIFT; >> >> if (pending != flushed) { >> - arch_flush_tlb_batched_pending(mm); >> + flush_tlb_mm(mm); > > I see that CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH is only implemented in > riscv (if !nommu), x86, arm64, and therefore we are only going to invoke > this for those arches which previously did the same anyway, so this is > safe. It's also the way it used to be done before arm64 joined the party and thought it could optimize by just issuing a DSB. I since discoved that the DSB approach is buggy so arm64 has now fallen back to flush_tlb_mm() so the reason for the original introduction of arch_flush_tlb_batched_pending() has gone. Thanks, Ryan > > Kinda wish we could avoid this ugly #ifdef #else #endif pattern here in > mm/rmap.c but probably necessary in this case. > >> /* >> * If the new TLB flushing is pending during flushing, leave >> * mm->tlb_flush_batched as is, to avoid losing flushing. >> -- >> 2.43.0 >>