From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id F0DFCC43458 for ; Mon, 29 Jun 2026 16:19:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C588C6B010F; Mon, 29 Jun 2026 12:19:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C098B6B0110; Mon, 29 Jun 2026 12:19:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AF7FC6B0113; Mon, 29 Jun 2026 12:19:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 6D67C6B010F for ; Mon, 29 Jun 2026 12:19:07 -0400 (EDT) Received: from smtpin28.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id D98AEA01D4 for ; Mon, 29 Jun 2026 16:19:06 +0000 (UTC) X-FDA: 84933459492.28.CA51E9B Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf28.hostedemail.com (Postfix) with ESMTP id 132A1C0006 for ; Mon, 29 Jun 2026 16:19:04 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ns1HpxUY; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf28.hostedemail.com: domain of vbabka@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=vbabka@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782749945; b=DoCoWmj2lF7WkLuiuyixzGWthUdogZYvUtHkghUoP221saWSVIRjoVhtOh+col+MZAVq51 NXnU0csFyf+ISCkieWBx6lr3TBUpF7mA54ooXTW1tM4SrOWBVJrkynoA6JUczcwejaOXZ4 f/bpLp8MVgbMwLgwvDullCO77d51GPM= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782749945; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ibo377gytuiH+zAA1DlGc+J0ntd31pmDjKTXixp+0P4=; b=LnSQLf7J8lMMWer3umc4jv2Cw8gie2Czorn/PeN1fReKhLUb1+1r3CFvrJe0jVtihD0KXx 1cE6kswM7jpjOW3Nz+Kb5gIRfIrQLcQSq5+MwdtaxjBr6TNmj+/NeQiGfmmya4oyEkRP7o vd5LXnZapw9JPY2UhGRT0dJYRlRuCrc= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ns1HpxUY; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf28.hostedemail.com: domain of vbabka@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=vbabka@kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 0B9A84067F; Mon, 29 Jun 2026 16:19:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A41D31F000E9; Mon, 29 Jun 2026 16:18:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782749943; bh=ibo377gytuiH+zAA1DlGc+J0ntd31pmDjKTXixp+0P4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ns1HpxUYzzA0svp08ErwLHFvPp9K9nG7flBt+w47R/JL1U5AzUbspZ4Lt25bMJOhu FungwpCqa4GLqwE/fgQSVyG4d9awwVP69g8+lVMKi7UqoGSwxzp1vdZSotrffSgg/5 hn5wVzTSZcZ2Q1TeUPhwO5cN7MAmH20AjPvQCKJNFh/22jzT8+WZGQIOK/umsgNP5U cq6YwkT9sGbO1s3eOcV3T/5lFzoRVxLob7iZzfrdRYCaMGlOXNgi56+1urTN1k/AF+ C5VvwCqza8WX2qypmPQGKPFs3f1++vvWdaTPA7PK8CQOgtzUJwfSkmmS/poMO1YwIf XPbmUXZ9UQMtQ== Message-ID: Date: Mon, 29 Jun 2026 18:18:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 00/13] Dynamic Kernel Stacks Content-Language: en-US To: Dave Hansen , Thomas Gleixner , Zach O'Keefe Cc: "H. Peter Anvin" , David Stevens , Pasha Tatashin , Linus Walleij , Will Deacon , Quentin Perret , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Andy Lutomirski , Xin Li , Peter Zijlstra , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , Kees Cook , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260424191456.2679717-1-stevensd@google.com> <6369e5ce-74e3-4c68-8053-d7d7d21b6955@zytor.com> <87pl1md7h0.ffs@fw13> <87qzm2b39k.ffs@fw13> <87mrwon5uw.ffs@fw13> <87cxxgly12.ffs@fw13> <5604a47b-9457-4162-bd23-720e29cf1983@intel.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <5604a47b-9457-4162-bd23-720e29cf1983@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 132A1C0006 X-Rspam-User: X-Stat-Signature: djemf5jo3585m99zjaqdxrg35q3j5xop X-HE-Tag: 1782749944-214166 X-HE-Meta: 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 E0ZHP21S ++auQ3pUrFV8DYP1hvZpeYNXAaHCPawLSiuNU1UZwKVAPC2iRin9SBnGIY1dvyTsp+HJXFAVCl/+snkrIvsBTnVBI0TxCuu43zxQQR90jhJQvCmzZtWzx/1WcMGQ+Sp3Bo4TF7vhHDp2DR+DEJpHuZQGoEheAbBX97rtNKym4J/sngv98A3qCD9RiKpsQkaUnpMgb0UvDWa4vZfB7GRWgKnHI7Er3AtGFSgNeQw+mGEMwAD7olYWxeNqn7CC0410O4EfFBC/0SX7IRvGyj0Os8Evy4zZxJRxlkwJD Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/29/26 18:02, Dave Hansen wrote: > On 6/23/26 14:58, Thomas Gleixner wrote: >> So as you already confirmed that the number of offenders is really low, >> it'd be definitely a worthwhile effort to fix that for everyone and also >> make the compiler people to get their act together 🙂 > > One other thing comes to mind... > > We have debugging options for looking at max stack depth, like > CONFIG_DEBUG_STACK_USAGE. But no distros seem to turn that on. There's > also some ftrace stuff, but I assume none of that is used at runtime either. > > Do we need some max stack depth instrumentation that folks will actually > turn on? It would be nice if we spat out warnings when folks went > through 12k (or 8k) of stack so there was a chance of closing the loop > and getting feedback from them. > > It could be done with really little overhead if the vmalloc()'d stacks > set Accessed=0 on their PTEs and then checked them near vfree(). The > PTEs are already getting touched there, so the cachelines should be hot > anyway. > > The granularity would only be 4k, but it would be so cheap that we could > turn it on universally. It would also be 100% deterministic. But it wouldn't tell you what was the large stack? Or we could try to print it inaccurately, and hope the non-overwritten deep part gives us enough insight? > There are, of course, more games that could be played with stack depth > checks on normal interrupts or NMIs. But those would be less deterministic. > > Thoughts?