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Fri, 25 Oct 2024 21:44:56 +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 BSAiL1gRHGfAWAAAD6G6ig (envelope-from ); Fri, 25 Oct 2024 21:44:56 +0000 Message-ID: <0ed7b766-1e7d-4f77-bf5a-bfa52d36ca8e@suse.cz> Date: Fri, 25 Oct 2024 23:44:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page mechanism Content-Language: en-US To: Lorenzo Stoakes , Andrew Morton Cc: Suren Baghdasaryan , "Liam R . Howlett" , Matthew Wilcox , "Paul E . McKenney" , Jann Horn , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song , Richard Henderson , 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: <415da1e6c5828d96db3af480d243a7f68ccabf6d.1729699916.git.lorenzo.stoakes@oracle.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: <415da1e6c5828d96db3af480d243a7f68ccabf6d.1729699916.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: swaenqs57m8exgeiwksx37ubz43mm5ck X-Rspamd-Queue-Id: 18245160020 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1729892685-988574 X-HE-Meta: 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 uLF2KuQ4 6aUu0elQmBYru8C+KVY6fL0Yc3X7RLzmk08L+2nqa5AJuSspOSrJfK1IjJWIfAUKpuXlGH3b4iA2IY9/QSEIiUhOVCg0gDgNIi07h46E3mu9JObpbFoJbn81n1KeTkDAuMNspxo1dE1PUEL1ic1B1mCz54OjiE77v/e8YuYi9g2YMORR5uOVLPRmMey1q1l/8mrCfd5mrT7+1XIiwtSDNb8OAab0fbWXkySHlmbUbbQTtMz7qFWaUlo4B3b7ov/KTgAP6ttQDleVhUwgCOrbYtSxHkGPIO+H0/WGmeEIhq8U/ERlpVcp38cmtnV9k4z3k+tVbJoBYhkZMS2ZZq1xU6GZqylvndLqoyhninKTIk5UyQpg= 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 10/23/24 18:24, Lorenzo Stoakes wrote: > Implement a new lightweight guard page feature, that is regions of userland > virtual memory that, when accessed, cause a fatal signal to arise. > > Currently users must establish PROT_NONE ranges to achieve this. > > However this is very costly memory-wise - we need a VMA for each and every > one of these regions AND they become unmergeable with surrounding VMAs. > > In addition repeated mmap() calls require repeated kernel context switches > and contention of the mmap lock to install these ranges, potentially also > having to unmap memory if installed over existing ranges. > > The lightweight guard approach eliminates the VMA cost altogether - rather > than establishing a PROT_NONE VMA, it operates at the level of page table > entries - establishing PTE markers such that accesses to them cause a fault > followed by a SIGSGEV signal being raised. > > This is achieved through the PTE marker mechanism, which we have already > extended to provide PTE_MARKER_GUARD, which we installed via the generic > page walking logic which we have extended for this purpose. > > These guard ranges are established with MADV_GUARD_INSTALL. If the range in > which they are installed contain any existing mappings, they will be > zapped, i.e. free the range and unmap memory (thus mimicking the behaviour > of MADV_DONTNEED in this respect). > > Any existing guard entries will be left untouched. There is therefore no > nesting of guarded pages. > > Guarded ranges are NOT cleared by MADV_DONTNEED nor MADV_FREE (in both > instances the memory range may be reused at which point a user would expect > guards to still be in place), but they are cleared via MADV_GUARD_REMOVE, > process teardown or unmapping of memory ranges. > > The guard property can be removed from ranges via MADV_GUARD_REMOVE. The > ranges over which this is applied, should they contain non-guard entries, > will be untouched, with only guard entries being cleared. > > We permit this operation on anonymous memory only, and only VMAs which are > non-special, non-huge and not mlock()'d (if we permitted this we'd have to > drop locked pages which would be rather counterintuitive). > > Racing page faults can cause repeated attempts to install guard pages that > are interrupted, result in a zap, and this process can end up being > repeated. If this happens more than would be expected in normal operation, > we rescind locks and retry the whole thing, which avoids lock contention in > this scenario. > > Suggested-by: Vlastimil Babka > Suggested-by: Jann Horn > Suggested-by: David Hildenbrand > Signed-off-by: Lorenzo Stoakes Reviewed-by: Vlastimil Babka > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -423,6 +423,12 @@ extern unsigned long highest_memmap_pfn; > */ > #define MAX_RECLAIM_RETRIES 16 > > +/* > + * Maximum number of attempts we make to install guard pages before we give up > + * and return -ERESTARTNOINTR to have userspace try again. > + */ > +#define MAX_MADVISE_GUARD_RETRIES 3 Can't we simply put this in mm/madvise.c ? Didn't find usage elsewhere.