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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id v130-20020a252f88000000b00b7767ca7490sm1755262ybv.45.2023.03.26.07.46.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 26 Mar 2023 07:46:24 -0700 (PDT) Date: Sun, 26 Mar 2023 10:46:22 -0400 From: Peter Xu To: David Hildenbrand Cc: Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Mike Rapoport , Nadav Amit , Axel Rasmussen , Andrea Arcangeli , Muhammad Usama Anjum , linux-stable Subject: Re: [PATCH v3] mm/hugetlb: Fix uffd wr-protection for CoW optimization path Message-ID: References: <20230324142620.2344140-1-peterx@redhat.com> <20230324222707.GA3046@monkey> <8a06be33-1b44-b992-f80a-8764810ebf3f@redhat.com> MIME-Version: 1.0 In-Reply-To: <8a06be33-1b44-b992-f80a-8764810ebf3f@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Queue-Id: C5287160019 X-Rspamd-Server: rspam01 X-Stat-Signature: dzk8m855igzjp3yhr8hufqy8d6qinekw X-HE-Tag: 1679841988-893512 X-HE-Meta: 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 mp73nO4b Obfe9iZTXnlj/c0507FEYk0eGxTcB7qfGfRj2yrg/19QpAGRK1yVEWFYoK+iJGoivk30+Vsg3uBuYVMsaP7F5iduC8kScK2cpkAigCiNC1QdYPAUbjka/2lWlukRYC403d3Z083DuOWpnSl4pwkUntY1FXCWHQkW9x0OCxuiRjWKge8hN849WprtjdiZNza9GstdtI532WOVgJSQYNfgzoHDQ9h00Z6BAhrG3A4f+fQMJ2bYCp+U0qs2ScLAt5pbuKmGHXeQsAnjlKVCrGtEh5Q0/qfwAh0rMR20rADj4HBRZpBYCYF4pEY9Xh7ot97iKb1/LmhjQeq/In3od/i0pX4vGcMHogdt5boB95TfFOe6MvUFud6LAq8YpRrXvhY+wjDxBsX08sdNvBQohgqZBHO0XgmOMdN2qXMtaVoIdmLDDCfjKMrAtlLCa5FgLjgkrPeMjz6FIk6q15Ik= 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: On Fri, Mar 24, 2023 at 11:36:53PM +0100, David Hildenbrand wrote: > > > @@ -5487,6 +5487,17 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma, > > > unsigned long haddr = address & huge_page_mask(h); > > > struct mmu_notifier_range range; > > > + /* > > > + * Never handle CoW for uffd-wp protected pages. It should be only > > > + * handled when the uffd-wp protection is removed. > > > + * > > > + * Note that only the CoW optimization path (in hugetlb_no_page()) > > > + * can trigger this, because hugetlb_fault() will always resolve > > > + * uffd-wp bit first. > > > + */ > > > + if (!unshare && huge_pte_uffd_wp(pte)) > > > + return 0; > > > > This looks correct. However, since the previous version looked correct I must > > ask. Can we have unshare set and huge_pte_uffd_wp true? If so, then it seems > > we would need to possibly propogate that uffd_wp to the new pte as in v2 Good point, thanks for spotting! > > We can. A reproducer would share an anon hugetlb page because parent and > child. In the parent, we would uffd-wp that page. We could trigger unsharing > by R/O-pinning that page. Right. This seems to be a separate bug.. It should be triggered in totally different context and much harder due to rare use of RO pins, meanwhile used with userfault-wp. If both of you agree, I can prepare a separate patch for this bug, and I'll better prepare a reproducer/selftest with it. -- Peter Xu