From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 F3C374657CC; Tue, 28 Jul 2026 15:03:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785250996; cv=none; b=f4xuxz+LTMdG4nYmrx/MzpiBCNPOEL5+gdQ2M0GTLxoTbGKnrfrr51QNMOwTtVEMd+w6fmlE2C6Z6pyGaxYQqYJ6GGPTz854FaGINMQ7jPwnQN53TwsV0RMwZie9f0wgdzP33DkdRLb1g7PVcZPUAt+PZEIqDNMze3o/V5We4J8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785250996; c=relaxed/simple; bh=2N83pgTb9rWXLPNPZC4FlvkefVz3L8EuP76ymrB5nt8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QfMz5lylajc8iFc+ytV985Djy0TraL1KzuJULRsQe0Ctc/aufkCPhjZWo/ekbI7dyEeVo2RvMR8g5ngbZvEsk8VCc9ypr5/kWkNIQHVmd5r5KX1rqZDhWOYP3m/4d3I9ChX5hKXUEbcdIG7J68776UUZ7R6g6lW9vZdB71lYbjc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BsT11Mus; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BsT11Mus" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7E3221F000E9; Tue, 28 Jul 2026 15:03:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785250994; bh=OZYCAEb0HM9rfGd3QRD8GMQog/bF2RXcJS7UIluiZL4=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=BsT11Musj5q8C0iTcuGYFJ6t+D6ns5bM8zQlELONuV/VX/yrCA018Wh0N7Gwlznfd aotiaq/I6OR8LKclH4M5+e4rAxmJyw3vUQECHwkeFMfQIQ/tFPlCTWglK3b/Tpzdww +bRNamfIQhuehUPoKSWXhm/ZLQvVUAWtUFMzGr+dfkJUvNs5Ryut3TSr4HBqIqxCdV 45BanpsTI0eHKnIwuq5OGl4NbtzaGlFQdEx9DUFUydqVDv7DsG4XLVGAH0lz5LJISE muvDh8wTByYOUEi4WYqtLE9IsNM7nj4Y4uHVDKRCrIrLpKMxJrdjaTi8nK3Kwr3pXt 8QQmczoQHS6GQ== Date: Tue, 28 Jul 2026 16:02:54 +0100 From: "Lorenzo Stoakes (ARM)" To: Peter Zijlstra Cc: Mike Rapoport , Dave Hansen , Dave Hansen , Andrew Morton , Andy Lutomirski , Borislav Petkov , David CARLIER , David Hildenbrand , Ingo Molnar , Jason Gunthorpe , Juergen Gross , Kevin Tian , Kiryl Shutsemau , "Liam R. Howlett" , Lu Baolu , "H. Peter Anvin" , Shakeel Butt , Suren Baghdasaryan , Thomas Gleixner , Toshi Kani , Vishal Moola , Vlastimil Babka , Will Deacon , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 1/5] x86/mm/pat: introcude cpa_lock() and cpa_unlock() Message-ID: References: <20260728-cpa-fixes-v1-0-2ed2352300b3@kernel.org> <20260728-cpa-fixes-v1-1-2ed2352300b3@kernel.org> <20260728142108.GW751831@noisy.programming.kicks-ass.net> <20260728143135.GG651302@noisy.programming.kicks-ass.net> <20260728145528.GI651302@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260728145528.GI651302@noisy.programming.kicks-ass.net> On Tue, Jul 28, 2026 at 04:55:28PM +0200, Peter Zijlstra wrote: > On Tue, Jul 28, 2026 at 05:46:30PM +0300, Mike Rapoport wrote: > > On Tue, Jul 28, 2026 at 04:31:35PM +0200, Peter Zijlstra wrote: > > > On Tue, Jul 28, 2026 at 07:30:27AM -0700, Dave Hansen wrote: > > > > On 7/28/26 07:21, Peter Zijlstra wrote: > > > > > There was already a patch merged that removed the shole debug_pagealloc > > > > > exception. Is that not better? > > > > > > > > As I'm scanning through email this morning, there's another issue that > > > > popped up with that patch. It's causing hangs on boot. > > > > > > > > It's looking like debug pagealloc not taking the lock is actually > > > > functional, not an optimization. Although, I hesitate to say > > > > "functional" and would prefer to use much less nice words to describe it. > > > > > > Yeah, lets figure out why that is before we retain this wart ;-) > > > > As Lorenzo said: > > > > __kernel_map_pages() can be called from irq context: > > > > < GFP_ATOMIC context > > > kfree() or whatever > > -> ... > > -> __free_pages_prepare() > > -> debug_pagealloc_unmap_pages() > > -> __kernel_map_pages() > > -> __change_page_attr_set_clr() > > -> cpa_lock > > > > The TLBI hack in __kernel_map_pages() makes me wonder how any of this is > correct to begin with. That comment isn't helping. > I think there's probably more horror shows there, it's a case of put out the most immediate fires, leave the probably remaining flaming trash pile for later ;) I thought x86 allowing arbitrary mm ptdump walks was crazy enough but this debug pagealloc stuff kinda pushes things further crazy-wise...