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[2003:cb:c707:3d00:d57f:b4c9:850e:d0b8]) by smtp.gmail.com with ESMTPSA id k6-20020a5d6d46000000b003434f526cb5sm32448217wri.95.2024.04.30.11.21.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Apr 2024 11:21:12 -0700 (PDT) Message-ID: <35c88b38-96e6-4092-a7e0-fd22f6d784cc@redhat.com> Date: Tue, 30 Apr 2024 20:21:11 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC][PATCH] uprobe: support for private hugetlb mappings To: Guillaume Morin , oleg@redhat.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, muchun.song@linux.dev References: <22fcde31-16c4-42d0-ad99-568173ec4dd0@redhat.com> <8d5314ac-5afe-41d4-9d27-9512cd96d21c@redhat.com> <385d3516-95bb-4ff9-9d60-ac4e46104130@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 30.04.24 17:22, Guillaume Morin wrote: > On 26 Apr 21:55, Guillaume Morin wrote: >> >> On 26 Apr 9:19, David Hildenbrand wrote: >>> A couple of points: >>> >>> a) Don't use page_mapcount(). Either folio_mapcount(), but likely you want >>> to check PageAnonExclusive. >>> >>> b) If you're not following the can_follow_write_pte/_pmd model, you are >>> doing something wrong :) >>> >>> c) The code was heavily changed in mm/mm-unstable. It was merged with t >>> the common code. >>> >>> Likely, in mm/mm-unstable, the existing can_follow_write_pte and >>> can_follow_write_pmd checks will already cover what you want in most cases. >>> >>> We'd need a can_follow_write_pud() to cover follow_huge_pud() and >>> (unfortunately) something to handle follow_hugepd() as well similarly. >>> >>> Copy-pasting what we do in can_follow_write_pte() and adjusting for >>> different PTE types is the right thing to do. Maybe now it's time to factor >>> out the common checks into a separate helper. >> >> I tried to get the hugepd stuff right but this was the first I heard >> about it :-) Afaict follow_huge_pmd and friends were already DTRT > > I got it working on top of your uprobes-cow branch with the foll force > patch sent friday. Still pretty lightly tested Sorry for not replying earlier, was busy with other stuff. I'll try getiing that stuff into shape and send it out soonish. > > I went with using one write uprobe function with some additional > branches. I went back and forth between that and making them 2 different > functions. All the folio_test_hugetlb() special casing is a bit suboptimal. Likely we want a separate variant, because we should be sing hugetlb PTE functions consistently (e.g., huge_pte_uffd_wp() vs pte_uffd_wp(), softdirty does not exist etc.) > > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c > index 2f4e88552d3f..8a33e380f7ea 100644 > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -83,6 +83,10 @@ static const struct fs_parameter_spec hugetlb_fs_parameters[] = { > {} > }; > > +bool hugetlbfs_mapping(struct address_space *mapping) { > + return mapping->a_ops == &hugetlbfs_aops; is_vm_hugetlb_page() might be what you are looking for. [...] > } > > -static void copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len) > +static void copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len, unsigned long page_mask) > { > void *kaddr = kmap_atomic(page); > - memcpy(dst, kaddr + (vaddr & ~PAGE_MASK), len); > + memcpy(dst, kaddr + (vaddr & ~page_mask), len); > kunmap_atomic(kaddr); > } > > -static void copy_to_page(struct page *page, unsigned long vaddr, const void *src, int len) > +static void copy_to_page(struct page *page, unsigned long vaddr, const void *src, int len, unsigned long page_mask) > { > void *kaddr = kmap_atomic(page); > - memcpy(kaddr + (vaddr & ~PAGE_MASK), src, len); > + memcpy(kaddr + (vaddr & ~page_mask), src, len); > kunmap_atomic(kaddr); > } These two changes really are rather ugly ... An why are they even required? We get a PAGE_SIZED-based subpage of a hugetlb page. We only kmap that one and copy within that one. In other words, I don't think the copy_from_page() and copy_to_page() changes are even required when we consistently work on subpages and not suddenly on head pages. > > -static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode) > +static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode, unsigned long page_mask) > { > uprobe_opcode_t old_opcode; > bool is_swbp; > @@ -191,7 +192,8 @@ static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t > * is a trap variant; uprobes always wins over any other (gdb) > * breakpoint. > */ > - copy_from_page(page, vaddr, &old_opcode, UPROBE_SWBP_INSN_SIZE); > + copy_from_page(page, vaddr, &old_opcode, UPROBE_SWBP_INSN_SIZE, > + page_mask); > is_swbp = is_swbp_insn(&old_opcode); > > if (is_swbp_insn(new_opcode)) { > @@ -376,8 +378,8 @@ struct uwo_data { > uprobe_opcode_t opcode; > }; > > -static int __write_opcode_pte(pte_t *ptep, unsigned long vaddr, > - unsigned long next, struct mm_walk *walk) > +static int __write_opcode(pte_t *ptep, unsigned long vaddr, > + unsigned long page_mask, struct mm_walk *walk) Unrelated alignment change. > { > struct uwo_data *data = walk->private;; > const bool is_register = !!is_swbp_insn(&data->opcode); > @@ -415,9 +417,12 @@ static int __write_opcode_pte(pte_t *ptep, unsigned long vaddr, > > /* Unmap + flush the TLB, such that we can write atomically .*/ > flush_cache_page(vma, vaddr, pte_pfn(pte)); > - pte = ptep_clear_flush(vma, vaddr, ptep); > + if (folio_test_hugetlb(folio)) > + pte = huge_ptep_clear_flush(vma, vaddr, ptep); > + else > + pte = ptep_clear_flush(vma, vaddr, ptep); > copy_to_page(page, data->opcode_vaddr, &data->opcode, > - UPROBE_SWBP_INSN_SIZE); > + UPROBE_SWBP_INSN_SIZE, page_mask); > > /* When unregistering, we may only zap a PTE if uffd is disabled ... */ > if (is_register || userfaultfd_missing(vma)) > @@ -443,13 +448,18 @@ static int __write_opcode_pte(pte_t *ptep, unsigned long vaddr, > if (!identical || folio_maybe_dma_pinned(folio)) > goto remap; > > - /* Zap it and try to reclaim swap space. */ > - dec_mm_counter(mm, MM_ANONPAGES); > - folio_remove_rmap_pte(folio, page, vma); > - if (!folio_mapped(folio) && folio_test_swapcache(folio) && > - folio_trylock(folio)) { > - folio_free_swap(folio); > - folio_unlock(folio); > + if (folio_test_hugetlb(folio)) { > + hugetlb_remove_rmap(folio); > + large = false; > + } else { > + /* Zap it and try to reclaim swap space. */ > + dec_mm_counter(mm, MM_ANONPAGES); > + folio_remove_rmap_pte(folio, page, vma); > + if (!folio_mapped(folio) && folio_test_swapcache(folio) && > + folio_trylock(folio)) { > + folio_free_swap(folio); > + folio_unlock(folio); > + } > } > folio_put(folio); > > @@ -461,11 +471,29 @@ static int __write_opcode_pte(pte_t *ptep, unsigned long vaddr, > */ > smp_wmb(); > /* We modified the page. Make sure to mark the PTE dirty. */ > - set_pte_at(mm, vaddr, ptep, pte_mkdirty(pte)); > + if (folio_test_hugetlb(folio)) > + set_huge_pte_at(mm , vaddr, ptep, huge_pte_mkdirty(pte), > + (~page_mask) + 1); > + else > + set_pte_at(mm, vaddr, ptep, pte_mkdirty(pte)); > return UWO_DONE; > } > > +static int __write_opcode_hugetlb(pte_t *ptep, unsigned long hmask, > + unsigned long vaddr, > + unsigned long next, struct mm_walk *walk) > +{ > + return __write_opcode(ptep, vaddr, hmask, walk); > +} > + > +static int __write_opcode_pte(pte_t *ptep, unsigned long vaddr, > + unsigned long next, struct mm_walk *walk) > +{ > + return __write_opcode(ptep, vaddr, PAGE_MASK, walk); > +} > + > static const struct mm_walk_ops write_opcode_ops = { > + .hugetlb_entry = __write_opcode_hugetlb, > .pte_entry = __write_opcode_pte, > .walk_lock = PGWALK_WRLOCK, > }; > @@ -492,7 +520,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma, > unsigned long opcode_vaddr, uprobe_opcode_t opcode) > { > struct uprobe *uprobe = container_of(auprobe, struct uprobe, arch); > - const unsigned long vaddr = opcode_vaddr & PAGE_MASK; > + unsigned long vaddr = opcode_vaddr & PAGE_MASK; > const bool is_register = !!is_swbp_insn(&opcode); > struct uwo_data data = { > .opcode = opcode, > @@ -503,6 +531,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma, > struct mmu_notifier_range range; > int ret, ref_ctr_updated = 0; > struct page *page; > + unsigned long page_size = PAGE_SIZE; > > if (WARN_ON_ONCE(!is_cow_mapping(vma->vm_flags))) > return -EINVAL; > @@ -521,7 +550,14 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma, > if (ret != 1) > goto out; > > - ret = verify_opcode(page, opcode_vaddr, &opcode); > + > + if (is_vm_hugetlb_page(vma)) { > + struct hstate *h = hstate_vma(vma); > + page_size = huge_page_size(h); > + vaddr &= huge_page_mask(h); > + page = compound_head(page); I think we should only adjust the range we pass to the mmu notifier and for walking the VMA range. But we should not adjust vaddr. Further, we should not adjust the page if possible ... ideally, we'll treat hugetlb folios just like large folios here and operate on subpages. Inside __write_opcode(), we can derive the the page of interest from data->opcode_vaddr. find_get_page() might need some though, if it won't return a subpage of a hugetlb folio. Should be solvable by a wrapper, though. > + } > + ret = verify_opcode(page, opcode_vaddr, &opcode, ~(page_size - 1)); > put_page(page); > if (ret <= 0) > goto out; -- Cheers, David / dhildenb