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 DF16A2EC0A4 for ; Tue, 15 Sep 2026 13:52:18 +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=1789480340; cv=none; b=JWAmaytP7kN0Y67skWzOsGFSK6rVmzLwgWNLQyy8IXlucso9q3LlLCtGy5liAxN+n2w8+g74YZb2s7eB9GP9MuQaz8w+E9muNgiVkxH4FkSL43ScADkgzgkfUfEAwxbXLaePyz8fz14Ur6ou+F7Eo3OVk7m/9nR+cwES0lNwl+E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789480340; c=relaxed/simple; bh=ZAms6xLFIiVySZXmTurNlRNYz1fQZdQMmujTnwJtQkU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=draf54Yoxwe9ZYb1b6pgV1PTO06BYihEy1hq0y8zbLOgzOzXMqCJ9bdAQiWEKFGEilzXw4UGp4Nl+Y0IapD4eQle/sjAYFtFLQVeSH3xmv6KnS8z60FZiXKEcJNKiUPAK6LHdTLqgROL4shsLyFWO147j1Xyn4xU1QvjfmJ2EM8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=it4mEL39; 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="it4mEL39" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B0831F00893; Tue, 15 Sep 2026 13:52:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789480338; bh=5JZvciHOubNz1++8I3c/2N9YUlCfXc/5f861xiy4ft0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=it4mEL392VOylMtWKucJN1H/SF3DAnw0vMuOMuzOxgyrfVosMCtYFPEOzDYEmBrW2 W+hJM+/RR/gY7ErtRBZSwl+WlJhSXohUCn6o1XeZ5ycAVGIW3kJ6OjOCPHwu/L+pGK 3ewVonc7r4UoKGfvtY6i8NU2P25btpAx/REc/e00UQY7GKiqtjsugzZ0EDzQXqhGbx DTQLHHJXWC7QgdC95T0OSpDwm2v9UDD/SPGVZgjCkxcnGnPS+6Bj6wVpNIvstFD8Uf JqsdvI//38sC3gA3EB0fPBHDwi5qqkPzu8hm4b42Ytx76sVcEa8g/ceU/zcGffVBHK 0czi5YHXvhY1A== Received: from phl-compute-01.internal (phl-compute-01.internal [10.202.2.41]) by mailfauth.ams.internal (Postfix) with ESMTP id 20534198003A; Tue, 15 Sep 2026 09:52:13 -0400 (EDT) Received: from phl-frontend-04 ([10.202.2.163]) by phl-compute-01.internal (MEProxy); Tue, 15 Sep 2026 09:52:15 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTGFaXHpQBoGzjJpzXuLzZEpEDoJVlEK8qfTCGlpZSscY902ocbS+NTIbNE8tMLKHV Kw+V8ruiMZ5vcsUwLmFvicjQ5fT2dEGX6BR2ofYNuwhWcszZXWDOzUPFZV9Kf2hTY0XyYu jgPRsVUGCvAoUBVHrbjcyoU/B85MGHEOvmNw+eGSCdPHSF+WLKvCB+LRHaJjwhCDtr3onu 9t7U2m3RKVIfG63unn994NKXoenEEAMJlO4Bca8sh/2dGdJkRJfrRO11fJi78OFB2d6mXQ f6/BbV5VWGgDSXWO0Q4c80Vk7TllbENgzRJLLQpIDfQ0PD5mAXpy4gZfEHx7Mr9L/IT0K6 qh4TshP2kn6kCNLC26NFy23vTdqmsw8g3megqLyVsGqfTaooE+RYvVeuOIYZy7Gn/syAK/ mNQESXCErDbA14ZJWZl10saMPTrc6xf8XeOzvS/LSSWkGC977QeRJhhixrzJbfu+n81g9e 1UH9yXgjzdTmINJ0W1c/2l/8tsZ5SsrH+DBIDUf7x1iNg5JRg4E76mGNLhLbU0PpzmXwuz fxsbi5T4JDhLZVv7EnZRfeABl7Tvmoe5VcDJ5trMTr/Py6Jb0oHqYqPMt54lsK/cZ45fqp eYKlOCmUSIfa9v0foUvG1fSeSBnE2eyER4tyPwmWpyxheKzoGzIAZR2ZhruA X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 15 Sep 2026 09:52:12 -0400 (EDT) Date: Tue, 15 Sep 2026 14:52:11 +0100 From: Kiryl Shutsemau To: Lance Yang Cc: Andrew Morton , "David Hildenbrand (Arm)" , ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, ljs@kernel.org, surenb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/1] mm/huge_memory: fix pgtable withdrawal for huge zero PMDs Message-ID: References: <20260912234635.db50397364858aa15f58f4d7@linux-foundation.org> <20260913072312.52111-1-lance.yang@linux.dev> <20260914111940.f7e2c72eac4a2df97a646793@linux-foundation.org> <30bcc70c-be07-4237-9bb1-554aa5b5c5c2@linux.dev> 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: <30bcc70c-be07-4237-9bb1-554aa5b5c5c2@linux.dev> On Tue, Sep 15, 2026 at 09:43:15PM +0800, Lance Yang wrote: > > > On 2026/9/15 02:19, Andrew Morton wrote: > > On Mon, 14 Sep 2026 16:29:00 +0200 "David Hildenbrand (Arm)" wrote: > > > > > On 9/14/26 12:59, Kiryl Shutsemau wrote: > > > > On Sun, Sep 13, 2026 at 03:23:12PM +0800, Lance Yang wrote: > > > > > > > > > > On Sat, Sep 12, 2026 at 11:46:35PM -0700, Andrew Morton wrote: > > > > > > > > > > > > > > > > > > That's the sort of thing we'd prefer to avoid. > > > > > > > > > > > > > > > > > > How real is this? Is there a reported-by:? Do you have a reproducer? > > > > > > > > > > Yes, I reproduced it on x86 with a small test module. It sets > > > > > VM_MIXEDMAP | VM_HUGEPAGE and calls vmf_insert_pfn_pmd() with > > > > > huge_zero_pfn, without touching the page tables directly. A full-PMD > > > > > munmap() crashes before the split series[1] as well. > > > > > > > > Ah. So there's no real bug upstream, right? > > > > > > Matches my understanding. > > > > Thanks. I'll remove cc:stable, move this into mm-unstable as a > > next-merge-window thing. > > Sounds good to me, thanks, Andrew! > > Kiryl, David, would you prefer the validation for raw-PFN mappings > of the huge zero page as a separate follow-up, or should that > validation replace this patch? wdyt I think this patch can be useful for graceful recovery if we somehow ended up with a zero page in a mapping where we shouldn't have one. A separate patch with validation would be great. -- Kiryl Shutsemau / Kirill A. Shutemov