From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0E39A1A9F94; Mon, 2 Feb 2026 13:42:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770039767; cv=none; b=Wh+bKpvCIe0413ezoS1w09vEeQmw/r8MKXHbHVxk2G1rTXyutp52Mi+d+TJUN/BlH0WDiHpOiw60fzfvZFx1vdfmZc2leub103g6X/7nd7u/pGnyy0IWCPH9VUijOLU/LhEoKvYJCecN9/QmaFzrosbK1zqjJyUpfBsI4Z4wFqA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770039767; c=relaxed/simple; bh=flMm1mESK5rb95gVoH/aoKPcdiwGr5AJdSSN5BWIm9w=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nbpxoxdpoQD5TTztgaeutddQLzOzfG4k5d71fyObqFcgwPdZDdPKZ6v9O+Yp28PvD0ZwLROfWu6qDHFa+W0lFMfjAiD5EvJSvUjSzrPahJ5++oislTVW7O+ATbeLocDZXj5N0oX4ICmKSUo2OHWx9MVcEOJAIOPIaCbGL6GpxxY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=cML3Fvhx; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="cML3Fvhx" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=FYBvBVbQkUIJwBmMc3AmsjMQCAxLks2LNy5Ykb6Sbho=; b=cML3FvhxJ1RsP4ckPgCxzFMSSr 9X3dZB/+mAIDMaVtX8ICs5bLtkwwc0zKhd8MTQKfuLTvwhz+EGXgnS53RvFh2k6KEDFqkrKNAMm6M Juo4Yb1Tr/4Sgit3UdkfczDLuNCxto9d2UbIUdz8V2s4dzvLQE+wzTyGsMF9GYawGWhFYGr/Y0upH RSMOH379lYU0kjXrDJKiwIJvPJg+TtTISWh7WOVQmjW4HKcBUMNtwepXv/Y3veDlKrdjnTttUCSid ZznXVmu493xJXmiHSYKXiZ4a/7XVyfCfcW3J2Z9BmrABABfgFvF3w+Z3AFCvIUhLqTdukfLSfBwTU 3bSohcPQ==; Received: from 2001-1c00-8d85-5700-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:5700:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vmuCI-0000000GYdY-0git; Mon, 02 Feb 2026 13:42:34 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id A9BFF3008E2; Mon, 02 Feb 2026 14:42:33 +0100 (CET) Date: Mon, 2 Feb 2026 14:42:33 +0100 From: Peter Zijlstra To: Lance Yang Cc: akpm@linux-foundation.org, david@kernel.org, dave.hansen@intel.com, dave.hansen@linux.intel.com, ypodemsk@redhat.com, hughd@google.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, 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, shy828301@gmail.com, riel@surriel.com, jannh@google.com, jgross@suse.com, seanjc@google.com, pbonzini@redhat.com, boris.ostrovsky@oracle.com, virtualization@lists.linux.dev, kvm@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ioworker0@gmail.com Subject: Re: [PATCH v4 1/3] mm: use targeted IPIs for TLB sync with lockless page table walkers Message-ID: <20260202134233.GG1395266@noisy.programming.kicks-ass.net> References: <20260202074557.16544-1-lance.yang@linux.dev> <20260202074557.16544-2-lance.yang@linux.dev> <20260202094245.GD2995752@noisy.programming.kicks-ass.net> <0f44dfb7-fce3-44c1-ab25-b013ba18a59b@linux.dev> <20260202125146.GC1395266@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Feb 02, 2026 at 09:23:07PM +0800, Lance Yang wrote: > Hmm... we need MB rather than RMB on the sync side. Is that correct? > > Walker: > [W]active_lockless_pt_walk_mm = mm -> MB -> [L]page-tables > > Sync: > [W]page-tables -> MB -> [L]active_lockless_pt_walk_mm > This can work -- but only if the walker and sync touch the same page-table address. Now, typically I would imagine they both share the p4d/pud address at the very least, right?