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Tue, 29 Oct 2024 10:32:27 +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 MkaFJLu5IGeENAAAD6G6ig (envelope-from ); Tue, 29 Oct 2024 10:32:27 +0000 Message-ID: Date: Tue, 29 Oct 2024 11:32:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 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: <6aafb5821bf209f277dfae0787abb2ef87a37542.1730123433.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: <6aafb5821bf209f277dfae0787abb2ef87a37542.1730123433.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: A3FCE4000B X-Stat-Signature: q4drmtw3skubiqqmxjdw16344gikpbmy X-HE-Tag: 1730197924-905599 X-HE-Meta: U2FsdGVkX1+QDJs59HG92lWbr7RxU7VXM6YU7jJ1pFqHaMRkwruCO798JgckgOHUWF1sw1F9yfZT/w4xwfWUpWBSVSuLZQjDb3TzFPCItYv2DLvetRvjv6V1SxfQuD5E0I17DLnU7RpbnbNOESzcgY758Kx8TfZPsuxuVJkPHN0OG00+sfULuBuXCyzEqF+KasdBwoheka3hk31JCW6NDo5dA/RWzCpD1XL0U1T5iv+L6AtuX91/P+8Y/CfysYMw+YRq1k8IZKZUIdFIxMymN4QdyZKnI3kk6eoYxinTcr4W/Ojl/tV+PW0UxJttOfWP7BUpO9yCG8M5kpTD0UhyxgeHCkn7lvsEF7B7BkzMNI3dVCscKLQfLj5BapB0Lwbt0NvMXc5ax5Hw5nVCpp5AAnz0DlnN1X0J6ok2YIEvAekbqORDtU92ASqpMfVJ31kw/KtcdsxznkXpq4FvUBgnYUkj5zBeFO1znmEKKhs1ttoLSJYkRgLSm41K+XY+cJHtDT11SCwv/G8bPKHF9uD4KDtt4rSDk+a7sG8nrRht/+GShbMSvwQXjGyC9ZjqNsd+Os9ZZYyJbDwF83arCQntb1Yr6VRixNgf89FVmTkTbAmiB/Hgguy8WzsgtO4qifC/+uOMtDt9aY8VjsWn1tMfLKLP6QqRauPq2Gzf9VTR12OE8SFcDkYlH/8/TK1lQmCGrb5NCqfdB6xXEelLdrsHp6NEhy2G3tjAdUsbClguEQypP5XkmwE6p0u1NeXu3DTazz85vsYnOXipBxNjWe/TcWMfL4m86jdeMxibrp/0WUoume7l9kXoKwR1oeo1b0SzBMuQScu7Q0TWJedGh9YliJ84bbkJlpH5N0jvQ6IbQDQ7wO2F6kOCYC05UosyzvaGdFqehljfCOfWXf5yC2Cw7abC4NHNPbOw/cggc2pQbBeJQgvDdBX3pjV4k9pWmnF4KSeIml5QNntFZ06/vZu VasuzfyW 2n1nuIXHdnrPPYVJxH+0KLUJceDG+RjNmXDfKAXPKWSvqci21CyBGLGX9JKmxZyPrlhyEeGI8dp+TIHSDIbiBGKFJDTC1B8o74+xsnWfIls9qLHe094rfjtzPXUNqQPTY3UqPj8WsgnJ0Ug7dNr/ROTmsBUWBu9bmbOfhHKQBPcsHPvVvIM8w/oRoFkuPoF3DK7F5RLPtrEAxxM61Yj6zkY3mBjTFoPIm4631l6rkOrqnhkt4rhiB7rwCiszKDeAHisDEb+yKLkBLgHVPRWJYLIaXAvOoT3Op+bL5jsIMJ8mlnm+7zXC44bJZpA2xvE9SZWixoKG6UsDYyoUPQ6vPIajnns/7N90YBAXFRftpoVpiS5k= 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 10/28/24 15:13, 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 Acked-by: Vlastimil Babka