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 3A84C41DEE7; Thu, 24 Sep 2026 07:07:57 +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=1790233683; cv=none; b=K3kR9qOCG3S9bFbqcIQoCzixvxSEoh1rJE4QZ91IB+I4Yt+rAwgjl3rZDAfj7mvuig3mmMkE4HSKVOu4mkk2zfUGuRLG+sl5Ta77UJCFMP25/mG0YjZep2Z3INiBUxGPF64Pk130aKJOV0C/ubuac8F3VpvnGMiHUg4zYZxwXBg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790233683; c=relaxed/simple; bh=Icj/hgctX9XKLRGJgAUX+/cnp4d0vWoBSdT27qFinws=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cXME208jXcrLuo6EGkx5UlzoCOpPFB+eAONaiAq51QibCR+MdH3d/Q61/JYN4pOAB/hka/hud+p8k+bGRPJzd4Yt0XqjFVcpOuwtRHKyC1VT+Kn7daA6WPapHJ8J2MI84EKRg8iIk5yHdbc3z+It2u+U5xzm9vh6rmHjO5jN4VI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KQJbdOLA; 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="KQJbdOLA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C128A1F000FF; Thu, 24 Sep 2026 07:07:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790233675; bh=mEMedDFi9mFkp6jCqF0VrbvDKNuIkj1/7PXdOKCq+kE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=KQJbdOLAdAoeUmQNZYOWsQ+KwIVQmJINzs5RxLAPvqdG8+KBfOeVGO8ywz2N9NiDK xwiiDNSHGv/1iLZNFDDuOyrlVMeHRxjM0ppRkOf3GTYhRiIPhq4As0s1tgvNcJQz9z 0ijoG8Xw3nf4hs4eZQ4hCBMBgwvmw0L/g9ZWWZpoNlLCYVOKPW6lHZ7G9Y47Tk6VpN qPeyAk+4a22CaO2FuE7Jeynwu99I5ZyvbEqc4l6srO7RdlFq/wGeW8EU9Rw04hfEPB PQmNs/ZdZ5ahp839B/m4yzyQgTiUWhxr5JRnXBVeyUnxG2dClGLnqyJ1m1/jFe2vss VlPOQIS/zdvtQ== Message-ID: <41a59ba9-039e-454f-8d31-f647db802ada@kernel.org> Date: Thu, 24 Sep 2026 09:07:45 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: don't defer freeing kernel page tables while booting To: Mikhail Gavrilov , Andrew Morton , Dave Hansen Cc: Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Vishal Moola , Ingo Molnar , Lu Baolu , Jason Gunthorpe , Steven Rostedt , x86@kernel.org, linux-mm@kvack.org, regressions@lists.linux.dev, linux-kernel@vger.kernel.org References: <20260924064321.23787-1-mikhail.v.gavrilov@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260924064321.23787-1-mikhail.v.gavrilov@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/24/26 08:43, Mikhail Gavrilov wrote: > Booting with a boot-time function tracer and a filter, for example > > ftrace=function ftrace_filter=pud_free_pmd_page > > panics on 7.3-rc4 as soon as the tracer starts: > > [ 23.531178] Starting tracer 'function' > [ 23.675800] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000038: 0000 [#1] SMP KASAN NOPTI > [ 23.819917] KASAN: null-ptr-deref in range [0x00000000000001c0-0x00000000000001c7] > [ 23.964025] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 7.3.0-rc4-fe2ec83746e5-with-fixes-v2+ #195 PREEMPT(undef) > [ 24.252248] RIP: 0010:__queue_work+0xab/0xf00 > [ 25.981629] Call Trace: > [ 26.125727] > [ 26.413912] ? pagetable_free_kernel+0x20/0x120 > [ 26.990283] queue_work_on+0x97/0xf0 > [ 27.134382] __cpa_collapse_large_pages+0x501/0x6f0 > [ 27.566662] cpa_flush+0x394/0x620 > [ 27.998953] change_page_attr_set_clr+0x321/0x4a0 > [ 29.151729] set_memory_rox+0xa2/0xf0 > [ 29.584018] create_trampoline+0x431/0x6f0 > ... > [ 44.343347] Kernel panic - not syncing: Attempted to kill the idle task! > > The boot-time tracer is started from early_trace_init(), which runs > before workqueue_init_early(). Making its trampoline read-only splits a > large page, and CPA collapses it again right away. The split table has > been a kernel page table since commit 9e4a3ec3411b > ("x86/mm/pat: Allocate split page tables as kernel page tables"), so the > collapse frees it through pagetable_free_kernel(), which queues work on > system_percpu_wq - still NULL at that point. > > The deferral exists so that IOMMUs using SVA can have their paging > structure caches flushed before a kernel page table is freed. While > system_state is still SYSTEM_BOOTING only the boot CPU runs and no IOMMU > has been initialised yet (on x86 that happens from pci_iommu_init(), a > rootfs_initcall), so there is nothing to flush. Free the table directly > in that case. > > Fixes: 9e4a3ec3411b ("x86/mm/pat: Allocate split page tables as kernel page tables") > Cc: stable@vger.kernel.org > Signed-off-by: Mikhail Gavrilov > --- > #regzbot introduced: 9e4a3ec3411b > > Tested on a Ryzen 9 7950X with a Radeon RX 7900 XTX, lockdep and KASAN > enabled, booting with the command line above plus earlycon=efifb so > that the oops is visible: > > 7.3-rc4 (fe2ec83746e5) panics as quoted > + revert of 9e4a3ec3411b boots > + this patch, 9e4a3ec3411b kept boots > > With this patch the boot-time tracer works as intended and records > pud_free_pmd_page() being called from vmap_p4d_range() during boot. > All three kernels also carry my pud_free_pmd_page() v2 patch and > unrelated local changes elsewhere (HID, sound/usb, Bluetooth, debugfs); > none of them is on this path. > > 9e4a3ec3411b is also in 7.2.7 and 6.18.53, together with the deferred > pagetable_free_kernel(); I have not tried those. > > mm/pgtable-generic.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c > index b91b1a98029c..2d9b4ba33b46 100644 > --- a/mm/pgtable-generic.c > +++ b/mm/pgtable-generic.c > @@ -440,6 +440,17 @@ static void kernel_pgtable_work_func(struct work_struct *work) > > void pagetable_free_kernel(struct ptdesc *pt) > { > + /* > + * While the system is still booting only the boot CPU runs and no > + * IOMMU has been set up, so nothing can be caching this table and > + * there is nothing to flush. The workqueue this defers to may not > + * exist yet either. > + */ > + if (system_state == SYSTEM_BOOTING) { > + __pagetable_free(pt); > + return; > + } > + > spin_lock(&kernel_pgtable_work.lock); > list_add(&pt->pt_list, &kernel_pgtable_work.list); > spin_unlock(&kernel_pgtable_work.lock); Should we instead simply skip the schedule_work(&kernel_pgtable_work.work); and rely on anybody freeing stuff later to just free that one alongside? That avoids throwing in more freeing handling. -- Cheers, David