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Fri, 25 Oct 2024 18:13:26 +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 HFLaG8bfG2edIQAAD6G6ig (envelope-from ); Fri, 25 Oct 2024 18:13:26 +0000 Message-ID: <8b1854b5-5c0a-43b1-aed7-aa4e8b8e8a1a@suse.cz> Date: Fri, 25 Oct 2024 20:13:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/5] mm: pagewalk: add the ability to install PTEs 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: <9be732fd0e897453116b433fe2f468ef7795602e.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: <9be732fd0e897453116b433fe2f468ef7795602e.1729699916.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 7ctpgf7r1zwo1ddydke9dngysdnzcgey X-Rspamd-Queue-Id: B9791140002 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1729879993-204514 X-HE-Meta: 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 3grVjL/M kQJg9CETc3sXgIfdWH0pe/q2nZgRY85ImYTyuqtvE19/2ET0b6ulT+x00aT18EAYrO9iYxDzCCtcOWhgOQf97cOmYXkrseioo8PCUpIjAe8x/+wU3BUao9K7WhbDygZF/14R1FWvYPWuz4aVCT/Xs6tekOmAjXhpPDzZWLpcMNYirc/e7RhjFzsZ/zGfLIxUA21oy/DRanUqZymnMOeyU2fhd3dAwnmcCLd2mu0dtyWDbLOXWiUngTw/mVsFw/s1UqVcorpEyd1Vjv16SuUWaOPkaM7ySAWVT9KR2xoCzR1wO1XeuXaNCArFUlAwd1SnrEaJltI639tSQKDNRDPuL9OJktg== 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: > The existing generic pagewalk logic permits the walking of page tables, > invoking callbacks at individual page table levels via user-provided > mm_walk_ops callbacks. > > This is useful for traversing existing page table entries, but precludes > the ability to establish new ones. > > Existing mechanism for performing a walk which also installs page table > entries if necessary are heavily duplicated throughout the kernel, each > with semantic differences from one another and largely unavailable for use > elsewhere. > > Rather than add yet another implementation, we extend the generic pagewalk > logic to enable the installation of page table entries by adding a new > install_pte() callback in mm_walk_ops. If this is specified, then upon > encountering a missing page table entry, we allocate and install a new one > and continue the traversal. > > If a THP huge page is encountered at either the PMD or PUD level we split > it only if there are ops->pte_entry() (or ops->pmd_entry at PUD level), > otherwise if there is only an ops->install_pte(), we avoid the unnecessary > split. > > We do not support hugetlb at this stage. > > If this function returns an error, or an allocation fails during the > operation, we abort the operation altogether. It is up to the caller to > deal appropriately with partially populated page table ranges. > > If install_pte() is defined, the semantics of pte_entry() change - this > callback is then only invoked if the entry already exists. This is a useful > property, as it allows a caller to handle existing PTEs while installing > new ones where necessary in the specified range. > > If install_pte() is not defined, then there is no functional difference to > this patch, so all existing logic will work precisely as it did before. > > As we only permit the installation of PTEs where a mapping does not already > exist there is no need for TLB management, however we do invoke > update_mmu_cache() for architectures which require manual maintenance of > mappings for other CPUs. > > We explicitly do not allow the existing page walk API to expose this > feature as it is dangerous and intended for internal mm use only. Therefore > we provide a new walk_page_range_mm() function exposed only to > mm/internal.h. > > Reviewed-by: Jann Horn > Signed-off-by: Lorenzo Stoakes Reviewed-by: Vlastimil Babka Just a small subjective suggestion in case you agree and there's a respin or followups: > @@ -109,18 +131,19 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, > > if (walk->action == ACTION_AGAIN) > goto again; > - > - /* > - * Check this here so we only break down trans_huge > - * pages when we _need_ to > - */ > - if ((!walk->vma && (pmd_leaf(*pmd) || !pmd_present(*pmd))) || > - walk->action == ACTION_CONTINUE || > - !(ops->pte_entry)) > + if (walk->action == ACTION_CONTINUE) > continue; > + if (!ops->install_pte && !ops->pte_entry) > + continue; /* Nothing to do. */ > + if (!ops->pte_entry && ops->install_pte && > + pmd_present(*pmd) && > + (pmd_trans_huge(*pmd) || pmd_devmap(*pmd))) > + continue; /* Avoid unnecessary split. */ Much better now, thanks, but maybe the last 2 parts could be: if (!ops->pte_entry) { if (!ops->install_pte) continue; /* Nothing to do. */ else if (pmd_present(*pmd) && (pmd_trans_huge(*pmd) || pmd_devmap(*pmd))) continue; /* Avoid unnecessary split. */ } Or at least put !ops->pte_entry first in both conditions? > if (walk->vma) > split_huge_pmd(walk->vma, pmd, addr); > + else if (pmd_leaf(*pmd) || !pmd_present(*pmd)) > + continue; /* Nothing to do. */ > > err = walk_pte_range(pmd, addr, next, walk); > if (err) > @@ -148,11 +171,14 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, > again: > next = pud_addr_end(addr, end); > if (pud_none(*pud)) { > - if (ops->pte_hole) > + if (ops->install_pte) > + err = __pmd_alloc(walk->mm, pud, addr); > + else if (ops->pte_hole) > err = ops->pte_hole(addr, next, depth, walk); > if (err) > break; > - continue; > + if (!ops->install_pte) > + continue; > } > > walk->action = ACTION_SUBTREE; > @@ -164,14 +190,20 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, > > if (walk->action == ACTION_AGAIN) > goto again; > - > - if ((!walk->vma && (pud_leaf(*pud) || !pud_present(*pud))) || > - walk->action == ACTION_CONTINUE || > - !(ops->pmd_entry || ops->pte_entry)) > + if (walk->action == ACTION_CONTINUE) > continue; > + if (!ops->install_pte && !ops->pte_entry && !ops->pmd_entry) > + continue; /* Nothing to do. */ > + if (!ops->pmd_entry && !ops->pte_entry && ops->install_pte && > + pud_present(*pud) && > + (pud_trans_huge(*pud) || pud_devmap(*pud))) > + continue; /* Avoid unnecessary split. */ Ditto. Thanks!