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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B878BEE49B4 for ; Tue, 30 Dec 2025 20:32:05 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2489E6B0088; Tue, 30 Dec 2025 15:32:05 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1CBFF6B0089; Tue, 30 Dec 2025 15:32:05 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0CEF66B008A; Tue, 30 Dec 2025 15:32:05 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id F3A8D6B0088 for ; Tue, 30 Dec 2025 15:32:04 -0500 (EST) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 9C9D91AEF3 for ; Tue, 30 Dec 2025 20:32:04 +0000 (UTC) X-FDA: 84277284168.02.7414D7D Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf26.hostedemail.com (Postfix) with ESMTP id C6BF1140004 for ; Tue, 30 Dec 2025 20:32:02 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=RFImDH+K; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf26.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1767126722; a=rsa-sha256; cv=none; b=nwRD+7w/Shly+BU5QEuoj5/EXp31VNJKCM3ipohCUrTALyGXv2H+AbVkFBj5ZWRvFSePtg Sd6gfKFGRyEOyYySSOWQKeJ/v8hBX0W7CYblqPHjLT6nOKtpQGkJlVnCUweKh1o6V54g6x bORB1riFmBINRb5LufVAc35j+BL2jPs= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=RFImDH+K; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf26.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1767126722; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=1x7fIpOg2y0mjOcKCE55ce3Dx6ueRBGLk5DeTPxsvd0=; b=YlFdhcowVKnwycEFYBUyRa2vGGFIXX3yf9bC3Pjwx6V/yEIwSLJC6LO8NBxZJj4kPVfMdL Ojjslwx9fEtXQVBh7M0+Rn43XFaiCzkaCuHr8ucqAP7GYfNfM0T0sHUqmR7bEKQyoYp4wB kI2RjLDbb5aCTKtA4yIkjW257UuOjr0= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 50EB9433B9; Tue, 30 Dec 2025 20:32:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2AB22C4CEFB; Tue, 30 Dec 2025 20:31:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767126721; bh=cndBsIdqWaO0mAWgypNK8SdnZmIn09dB7jgukNbm22w=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RFImDH+KE8o0n4QR10H4g03pXnoFVlnXi95t2jkVwzBvm3iUyPAFFUDsKjAGKDS6O 1384jK4bXsTUKQREFbHc8T14YsyjZ+5+N8hJOzl4uztvoAtlBb3DmFTDK6k9t9bzqf ZJEBD9PvLpA5IArOlpb5q2+k+IMGVc11Rw89kMQbSOPhEt7RAZUMFXt8wVmNpDEzR+ 1c2TTUYBxQn4PU1f477EIXkUnOabLBlYBPHtygvfN3TT098hZXv+M8VvSEg+q82w0L Lyje7kaCTXZXIiAkmhIbGXmDPlFCtiuzom3Hy4MBH5P6HZtutqAiPtkJM6DqHmd2LZ zJ4zf1lkPnAhw== Message-ID: <725b85bf-ff5e-45d6-991e-d92598779f98@kernel.org> Date: Tue, 30 Dec 2025 21:31:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] mm/tlb: allow architectures to skip redundant TLB sync IPIs To: Lance Yang , akpm@linux-foundation.org Cc: will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, ioworker0@gmail.com, shy828301@gmail.com, riel@surriel.com, jannh@google.com, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251229145245.85452-1-lance.yang@linux.dev> <20251229145245.85452-2-lance.yang@linux.dev> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251229145245.85452-2-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C6BF1140004 X-Stat-Signature: nfd8eirn7kjzyy9tr7iy9romoybimby7 X-HE-Tag: 1767126722-286727 X-HE-Meta: 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 wvdiBWu/ zztZuT91M3QhN/Hh69booAMaIbDfJfYfUnTb7kiwurIqW2EOvyvIrbPELiI76m0ToQv6O2hQOuzFtRci6F7+Yj7hcHD/LmLur5Ad3vlKJ1a6fFQFOobIB2W6Xz4RwX7LXqht2reiwqXM/a/4wkDiex81495FW/MoWtBKwpJLgN806AjAPpV1rfBQlJkZYWhbgMmCN5Rm1l2FZm8JuExSC1W7uYf2kYXOvF03OwSJUc5lRY9sKlvMIgXXhsw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/29/25 15:52, Lance Yang wrote: > From: Lance Yang > > When unsharing hugetlb PMD page tables, we currently send two IPIs: one > for TLB invalidation, and another to synchronize with concurrent GUP-fast > walkers. > > However, if the TLB flush already reaches all CPUs, the second IPI is > redundant. GUP-fast runs with IRQs disabled, so when the TLB flush IPI > completes, any concurrent GUP-fast must have finished. > > Add tlb_table_flush_implies_ipi_broadcast() to let architectures indicate > their TLB flush provides full synchronization, enabling the redundant IPI > to be skipped. > > Suggested-by: David Hildenbrand (Red Hat) > Signed-off-by: Lance Yang > --- > include/asm-generic/tlb.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h > index 4d679d2a206b..e8d99b5e831f 100644 > --- a/include/asm-generic/tlb.h > +++ b/include/asm-generic/tlb.h > @@ -261,6 +261,20 @@ static inline void tlb_remove_table_sync_one(void) { } > > #endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */ > > +/* > + * Architectures can override if their TLB flush already broadcasts IPIs to all > + * CPUs when freeing or unsharing page tables. > + * > + * Return true only when the flush guarantees: > + * - IPIs reach all CPUs with potentially stale paging-structure cache entries > + * - Synchronization with IRQ-disabled code like GUP-fast > + */ > +#ifndef tlb_table_flush_implies_ipi_broadcast > +static inline bool tlb_table_flush_implies_ipi_broadcast(void) > +{ > + return false; > +} > +#endif > > #ifndef CONFIG_MMU_GATHER_NO_GATHER > /* This should likely get squashed into patch #3. Patch #1 itself does not add a lot of value to be had separately. So best to squash both and have them as #1, to then implement it in #2 for x86. -- Cheers David