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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774428557; bh=TT8uCC50j5LON03XR+370wuR3/hgIDrv5RVCNkZprKc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gOISyRJN7vnYb+a/9jSJvZ1Y0J7sMVdE8pgl6Qji+DvsCJqcC4BVCv68kwZfJJjy2 RDzK3p4kbjpCa55e4ny9V+kMgzJB9shsVDKfuICtT/xbN6IIg2KqLkWQulSMR835Qr WFru7gPZ4qyk8gJ0Wax9oFoJK93Oc8aOL58m2h/DmGNOJlsCmGc8DBoCpwRumHT3yj sSMNs7E124BWgw2c8A9k59eHr1PPPagfSc16f0GPLTvINVasePOp4P5HOnCP3nsHwy VyEDkmBDFhHrptT9HVUR+wo6l17hvNTe6h6XVldBPR/MI6ODTymIAaEN52neaGN53K OVTU0Fz+5sM3g== Message-ID: <1075f7a0-232f-4268-94b3-573d11c4203f@kernel.org> Date: Wed, 25 Mar 2026 09:49:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm/userfaultfd: fix hugetlb fault mutex hash calculation To: Andrew Morton , Jianhui Zhou , Muchun Song , Oscar Salvador , Mike Rapoport Cc: jane.chu@oracle.com, Peter Xu , Andrea Arcangeli , Mike Kravetz , SeongJae Park , Hugh Dickins , Sidhartha Kumar , Jonas Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, syzbot+f525fd79634858f478e7@syzkaller.appspotmail.com References: <20260306140332.171078-1-jianhuizzzzz@gmail.com> <20260310110526.335749-1-jianhuizzzzz@gmail.com> <12e822c4-a4f2-4447-80b9-2eec35a03188@oracle.com> <20260324170311.dc5b54fe0765f2e680e3cc90@linux-foundation.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: uqwx3eo7xq7zdj5odtbqummcfo7hskd4 X-Rspamd-Queue-Id: 2FBDB160003 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1774428557-379823 X-HE-Meta: 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 /yObaTk2 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/25/26 01:03, Andrew Morton wrote: > On Wed, 11 Mar 2026 18:54:26 +0800 Jianhui Zhou wrote: > >> On Tue, Mar 10, 2026 at 12:47:07PM -0700, jane.chu@oracle.com wrote: >>> Just wondering whether making the shift explicit here instead of >>> introducing another hugetlb helper might be sufficient? >>> >>> idx >>= huge_page_order(hstate_vma(vma)); >> >> That would work for hugetlb VMAs since both (address - vm_start) and >> vm_pgoff are guaranteed to be huge page aligned. However, David >> suggested introducing hugetlb_linear_page_index() to provide a cleaner >> API that mirrors linear_page_index(), so I kept this approach. >> > > Thanks. > > Would anyone like to review this cc:stable patch for us? I would hope the hugetlb+userfaultfd submaintainers could have a detailed look! Moving them to "To:" One of the issue why this doesn't get more attention might be posting a new revision as reply to an old revision, which is an anti-pattern :) > > > From: Jianhui Zhou > Subject: mm/userfaultfd: fix hugetlb fault mutex hash calculation > Date: Tue, 10 Mar 2026 19:05:26 +0800 > > In mfill_atomic_hugetlb(), linear_page_index() is used to calculate the > page index for hugetlb_fault_mutex_hash(). However, linear_page_index() > returns the index in PAGE_SIZE units, while hugetlb_fault_mutex_hash() > expects the index in huge page units. This mismatch means that different > addresses within the same huge page can produce different hash values, > leading to the use of different mutexes for the same huge page. This can > cause races between faulting threads, which can corrupt the reservation > map and trigger the BUG_ON in resv_map_release(). > > Fix this by introducing hugetlb_linear_page_index(), which returns the > page index in huge page granularity, and using it in place of > linear_page_index(). > > Link: https://lkml.kernel.org/r/20260310110526.335749-1-jianhuizzzzz@gmail.com > Fixes: a08c7193e4f1 ("mm/filemap: remove hugetlb special casing in filemap.c") > Signed-off-by: Jianhui Zhou > Reported-by: syzbot+f525fd79634858f478e7@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=f525fd79634858f478e7 > Cc: Andrea Arcangeli > Cc: David Hildenbrand > Cc: Hugh Dickins > Cc: JonasZhou > Cc: Mike Rapoport > Cc: Muchun Song > Cc: Oscar Salvador > Cc: Peter Xu > Cc: SeongJae Park > Cc: Sidhartha Kumar > Cc: > Signed-off-by: Andrew Morton > --- > > include/linux/hugetlb.h | 17 +++++++++++++++++ > mm/userfaultfd.c | 2 +- > 2 files changed, 18 insertions(+), 1 deletion(-) > > --- a/include/linux/hugetlb.h~mm-userfaultfd-fix-hugetlb-fault-mutex-hash-calculation > +++ a/include/linux/hugetlb.h > @@ -796,6 +796,23 @@ static inline unsigned huge_page_shift(s > return h->order + PAGE_SHIFT; > } > > +/** > + * hugetlb_linear_page_index() - linear_page_index() but in hugetlb > + * page size granularity. > + * @vma: the hugetlb VMA > + * @address: the virtual address within the VMA > + * > + * Return: the page offset within the mapping in huge page units. > + */ > +static inline pgoff_t hugetlb_linear_page_index(struct vm_area_struct *vma, > + unsigned long address) > +{ > + struct hstate *h = hstate_vma(vma); > + > + return ((address - vma->vm_start) >> huge_page_shift(h)) + > + (vma->vm_pgoff >> huge_page_order(h)); > +} > + > static inline bool order_is_gigantic(unsigned int order) > { > return order > MAX_PAGE_ORDER; > --- a/mm/userfaultfd.c~mm-userfaultfd-fix-hugetlb-fault-mutex-hash-calculation > +++ a/mm/userfaultfd.c > @@ -573,7 +573,7 @@ retry: > * in the case of shared pmds. fault mutex prevents > * races with other faulting threads. > */ > - idx = linear_page_index(dst_vma, dst_addr); > + idx = hugetlb_linear_page_index(dst_vma, dst_addr); > mapping = dst_vma->vm_file->f_mapping; > hash = hugetlb_fault_mutex_hash(mapping, idx); > mutex_lock(&hugetlb_fault_mutex_table[hash]); > _ > Let's take a look at other hugetlb_fault_mutex_hash() users: * remove_inode_hugepages: uses folio->index >> huge_page_order(h) -> hugetlb granularity * hugetlbfs_fallocate(): start/index is in hugetlb granularity -> hugetlb granularity * memfd_alloc_folio(): idx >>= huge_page_order(h); -> hugetlb granularity * hugetlb_wp(): uses vma_hugecache_offset() -> hugetlb granularity * hugetlb_handle_userfault(): uses vmf->pgoff, which hugetlb_fault() sets to vma_hugecache_offset() -> hugetlb granularity * hugetlb_no_page(): similarly uses vmf->pgoff -> hugetlb granularity * hugetlb_fault(): similarly uses vmf->pgoff -> hugetlb granularity So this change here looks good to me Reviewed-by: David Hildenbrand (Arm) But it raises the question: (1) should be convert all that to just operate on the ordinary index, such that we don't even need hugetlb_linear_page_index()? That would be an addon patch. (2) Alternatively, could we replace all users of vma_hugecache_offset() by the much cleaner hugetlb_linear_page_index() ? In general, I think we should look into having idx/vmf->pgoff being consistent with the remainder of MM, converting all code in hugetlb to do that. Any takers? -- Cheers, David