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 EF9B230C146; Tue, 28 Jul 2026 15:33:52 +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=1785252834; cv=none; b=hPNxF34oCXNdR6KYYyj8IBdmG/3Z0YDyl5qPmtKrel+ct064yZj+kTQWVrJKfHEf0297jZh+rKinJkTsSCM2Yj+m9JpZCD03AJ+SqsOi34GM6BFspSf8wZ+1PLmcE3WgT1E8Rkt6s44q6iROxZonVIctLmgSDqAtBLoczVsBgoY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785252834; c=relaxed/simple; bh=zQIwOSKn/0R8Y2guuiO/EQFjFuK6aMrhavXHWbZlyhw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Bu3Qy8vuAdBSJ4B08z+WKNItH3FzJieBDc8VeamvxeeUlcXLDsxQnqbhwEQTR3BIMRPA78LUItYEyEWR026GgwpH/HNHjPdxvOHAKyJ5H1SllG1ax3+CjrAoRm9+6tj98eATfgNkLPkZGULyi5vMjDhqYvnfr2wTTJ5bfkXseqU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=ZR7XTAvt; 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=pass 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="ZR7XTAvt" 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=MtI8BjVNz9fvIWLLabGAXhTyjAUw+ny5VCHWBMfAP7U=; b=ZR7XTAvtNIKJro36JxE/8l5Q/W ReI+Qiwt7PsTt2gjKRFN+94VxnT4QcNzzua3897tbbBK2zoDqEElZSnqusWc70POKhKhprFcGTNel J2sUYUxGJAlwLorD5mn+tYu+56aQUqbZpxu3dhCYYZ8pNYNCHs42fILaFYFNMHG8B71NmI7hFnLUd 3FMIbQlnGUw6or7BLKSbHdVRtXp2cacvktYZFtfsB6ZLR6NRE/Ww4KeGKcd3/39EpDCsALZVL8P4W 03P8v3ZO3dhnkJHv1fe24ssYJX/CLUcU6wNX4smqEXCVYrj7WjL9XaT5srV1LsLj+wgcalmaoKbbM ZA0j0ndQ==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wojoM-0000000DaEn-0Vwv; Tue, 28 Jul 2026 15:33:42 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id A12183004AB; Tue, 28 Jul 2026 17:33:41 +0200 (CEST) Date: Tue, 28 Jul 2026 17:33:41 +0200 From: Peter Zijlstra To: "Lorenzo Stoakes (ARM)" 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: <20260728153341.GY751831@noisy.programming.kicks-ass.net> 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> <20260728150126.GC921102@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: iommu@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 Tue, Jul 28, 2026 at 04:20:10PM +0100, Lorenzo Stoakes (ARM) wrote: > On Tue, Jul 28, 2026 at 05:01:26PM +0200, Peter Zijlstra wrote: > > 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. > > > > > > > Also, the 'atomic context' usage hereabout seems confused. In particular > > the issue is with IRQ-disabled context, they are not the same thing. > > I mean yeah the IRQs being off is the issue with holding the lock over an IPI, a > softirq allocating GFP_ATOMIC won't be a problem for that, but I think all the > conclusions are still the same. preempt_disable() is an 'atomic context', but does not present the problem. Anyway, yes not saying the conclusions are wrong, just that the wording is confusing at heck.