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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43DF1D1713F for ; Mon, 21 Oct 2024 21:35:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B53D76B009C; Mon, 21 Oct 2024 17:35:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id ADC7C6B009E; Mon, 21 Oct 2024 17:35:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8E0BD6B00A1; Mon, 21 Oct 2024 17:35:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 6DEEF6B009C for ; Mon, 21 Oct 2024 17:35:29 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 97D5DA0B8A for ; Mon, 21 Oct 2024 21:35:00 +0000 (UTC) X-FDA: 82698915684.11.830D319 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) by imf10.hostedemail.com (Postfix) with ESMTP id 07172C001B for ; Mon, 21 Oct 2024 21:35:19 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=cFvJRvVG; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=rvkCmFuW; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=cFvJRvVG; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=rvkCmFuW; dmarc=none; spf=pass (imf10.hostedemail.com: domain of vbabka@suse.cz designates 195.135.223.131 as permitted sender) smtp.mailfrom=vbabka@suse.cz ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1729546490; a=rsa-sha256; cv=none; b=D47FBZFpd9V1GVYJUg8ggz2Z7EcCdWZXjNG901K3i5Vyor/Z2UK8coEj0JKld9d2PbuR9E l0KZtY9esxfrkswpYksOGEJIE4noTeGYxg+plibUFMTXYgB4euuzhzZ/vhaiC/ErSWP4/j /nAbgH2RORCEdyGnrq3C7rk7s04TQ3A= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=cFvJRvVG; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=rvkCmFuW; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=cFvJRvVG; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=rvkCmFuW; dmarc=none; spf=pass (imf10.hostedemail.com: domain of vbabka@suse.cz designates 195.135.223.131 as permitted sender) smtp.mailfrom=vbabka@suse.cz ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1729546490; 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=LoXARsrdlSvPgawSsVLMjLV+iv37QoPv7vysgYEzKsg=; b=GRXgw91c97CHty+O3ndGp6aAFisJTAshT9EKOiM+M1D9CofoW4Ecx+ExXRflwTfNoN0fd4 NcYvzVbqr0vovnpjK0mOsGBa3QX5eQD2peDdXOHhCiyttfwCLgzX94s/1IrKdTNfrKbetR QxQUL3H3s/eSNKSII1vzRIgpS/6xN54= Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id BCD671F8A6; Mon, 21 Oct 2024 21:35:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1729546524; h=from:from:reply-to: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:autocrypt:autocrypt; bh=LoXARsrdlSvPgawSsVLMjLV+iv37QoPv7vysgYEzKsg=; b=cFvJRvVGMF2wcUPN8PdbgZVakQEPaxUr7/nF4sjo1tow3oF/BDbBvO8qcWD0uNZBDdNbpv PizfmLSkBHCS8cB5yUU2VZELh8PoVKg8ru3xTyjJxmVT2Eji1OLlm6tkRa9TLOeijc4H0n opZyaVSpAM+v0NBPIhudvoPCficNAlQ= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1729546524; h=from:from:reply-to: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:autocrypt:autocrypt; bh=LoXARsrdlSvPgawSsVLMjLV+iv37QoPv7vysgYEzKsg=; b=rvkCmFuWiO6/tJTeMTWfd3dpHmsiE12L6ZoIVIuep/6wUwx2k6C+Z3nrFXr0WaGiefz2EB lCjFk+wgkLnYPuBg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1729546524; h=from:from:reply-to: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:autocrypt:autocrypt; bh=LoXARsrdlSvPgawSsVLMjLV+iv37QoPv7vysgYEzKsg=; b=cFvJRvVGMF2wcUPN8PdbgZVakQEPaxUr7/nF4sjo1tow3oF/BDbBvO8qcWD0uNZBDdNbpv PizfmLSkBHCS8cB5yUU2VZELh8PoVKg8ru3xTyjJxmVT2Eji1OLlm6tkRa9TLOeijc4H0n opZyaVSpAM+v0NBPIhudvoPCficNAlQ= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1729546524; h=from:from:reply-to: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:autocrypt:autocrypt; bh=LoXARsrdlSvPgawSsVLMjLV+iv37QoPv7vysgYEzKsg=; b=rvkCmFuWiO6/tJTeMTWfd3dpHmsiE12L6ZoIVIuep/6wUwx2k6C+Z3nrFXr0WaGiefz2EB lCjFk+wgkLnYPuBg== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 7B3FC136DC; Mon, 21 Oct 2024 21:35:24 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id yI9oHRzJFmeBUwAAD6G6ig (envelope-from ); Mon, 21 Oct 2024 21:35:24 +0000 Message-ID: Date: Mon, 21 Oct 2024 23:35:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/5] mm: madvise: implement lightweight guard page mechanism Content-Language: en-US To: David Hildenbrand , Lorenzo Stoakes Cc: Andrew Morton , Suren Baghdasaryan , "Liam R . Howlett" , Matthew Wilcox , "Paul E . McKenney" , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song , Richard Henderson , Ivan Kokshaysky , Matt Turner , Thomas Bogendoerfer , "James E . J . Bottomley" , Helge Deller , Chris Zankel , Max Filippov , Arnd Bergmann , linux-alpha@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-arch@vger.kernel.org, Shuah Khan , Christian Brauner , linux-kselftest@vger.kernel.org, Sidhartha Kumar , Jeff Xu , Christoph Hellwig , linux-api@vger.kernel.org, John Hubbard References: <6c282299-506f-45c9-9ddc-9ef4de582394@redhat.com> <9727ada4-0048-499b-a43f-ac0a625bae5d@redhat.com> <73134e10-19eb-4e52-b87f-5fbfd322b575@lucifer.local> <0f7a6b69-5706-4010-ba7a-68a071922c80@redhat.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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 BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <0f7a6b69-5706-4010-ba7a-68a071922c80@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspam-User: X-Stat-Signature: 8qzazgqqkmh9co4ohkcr3x4eeskgut3a X-Rspamd-Queue-Id: 07172C001B X-Rspamd-Server: rspam02 X-HE-Tag: 1729546519-334796 X-HE-Meta: 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 brguSjRy gImyr9A8nCm0ahcLXmHh11xaOlxQVQhkv2dkUazwnEsmeqgFgoAmNgdF0rLaEDOq6fuUkNMbI0cPkYX8AvKXprySgfp5g0dt1yTjJDrl2phqtadO4eBkF7+F5nblzfphYPDXEkhVdn46qD7l6y1ZzvIsMwis+AuOLzHuuSrggZIfbBqrviA9wpn4HgBhrg1YcNhKdoOQ2NS0vi8c4JYfFYqogK96iuZFnRnYCAD6ewQeW9z9jEkGYExAoCLdf0PhDrmnSzztcuWaeXY/AG+Vd0VU1y6qsp5itnVqGhKVolkAHz6S202SO9q/iTjbV2gbyzJO6j1vKKwG8MGr8KFPBviAZJw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/21/24 23:20, David Hildenbrand wrote: >> I don't think there's really any value in that. There's just no sensible >> situation in which a user would care about this I don't think. > > Making sure nobody touches an area, and wile doing that somebody already > touched that area? I guess it could be worked around by > mprotect(PROT_NONE),madvise(GUARD),mprotect(PROT_READ|PROT_WRITE) ... > which is not particularly nice :) > >> >> And if you're saying 'hey do MADV_DONTNEED if this fails and keep trying!' >> then why not just do that in the kernel? > > Heh, no! > > If user space doesn't expect there to be something, it should *fail*. > That's likely going to be the majority of use cases for guard pages > (happy to be told otherwise). No retry. > > And if user space expects there to be something it should zap ahead of > time (which some allocators maybe already do to free up memory after > free()) to then install the guard. No retry. > > There is this case where user space might be unsure. There, it might > make sense to retry exactly once. I've thought so too and the RFC was implemented like this, but Jann came up with a scenario where a THP can cause the range including our to-be-installed guard pte to be populated even if the userspace is not trying to access that exact address, see here: https://lore.kernel.org/all/CAG48ez3vqbqyWb4bLdpqSUnhwqGo2OQetecNhEGPdCGDr94nbQ@mail.gmail.com/ So unless we can't *reliably* detect that userspace is really shooting itself in the foot and return a failure to install guard pte *only* in that case (which would be useful), and not horribly complicate everything to ensure that reliability and to avoid false positives due to races with THP's, then it's probably better to just retry as this version does. >> >> Trying to explain to a user 'hey this is for installing guard pages but if >> there's a facing fault it'll fail and that could keep happening and then >> you'll have to zap and maybe in a loop' just... seems like a bloody awful >> interface? > > Hope my example above made it clearer. This "retry forever until it > works" use case doesn't quite make sense to me, but I might just be > missing something important. > > But again, I have to do more reading on the history of the current > approach ... and it's fairly late here. Yeah see the RFC thread linked above.