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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6cb3b66b5a8sm50841946d6.79.2024.10.01.08.10.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Oct 2024 08:10:03 -0700 (PDT) Date: Tue, 1 Oct 2024 11:10:02 -0400 From: Peter Xu To: Ryan Roberts Cc: David Hildenbrand , Mark Rutland , Linux-MM , Mike Rapoport Subject: Re: Warning on mremapped uffd-wp memory Message-ID: References: <810b44a8-d2ae-4107-b665-5a42eae2d948@arm.com> <520f4933-7164-4559-b6a9-8f28c1bff0d1@redhat.com> <7e52ca0b-39df-4979-8b16-9880e5a7149c@redhat.com> <97c7b531-daeb-468f-af2a-31980f6f6a84@redhat.com> <29404449-fcbe-4d54-85ce-44da0b202243@arm.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 6BCC3120003 X-Stat-Signature: pot8coegb5w9ai4ackxqohryywgxqmw5 X-Rspam-User: X-HE-Tag: 1727795408-178664 X-HE-Meta: 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 jEuun2yB qawdWVxCXOjmgWs6zvBT8AYhsgTU+qnq3LSKdRggdtriVDjA7QNr3I1tflfG4vwusWYlDxwb/Gu9PGuBZWS3sD8QGbhtBpTtWiG6wjxHnu21ZqwRBoxsxI/+F+WqVXYsDYEgnsOO8Lqz6aMh7nx1F+vidLMe+HjgD+d+gzCZBZzbEudsAnFl28iE/BGtGsu3e3guI9wF1zaXvQggvgCt26+D0/4SkTE6prMoPg/SJb5aaIXCkEnfXXTjjqqWKfK89/s7BxaaBTHAR+6M4cMYlW8zzhUpapHeRGWd5l+eK6fBjgZYH/WybJTfS3KQf03rUsYxp8nAPmIXHSMhVFGtFWHzkqnTnGuwwfdmP4H+DV28ANto7yxpGH64cpA== 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 Tue, Oct 01, 2024 at 03:27:48PM +0100, Ryan Roberts wrote: > Hi Peter, > > On 08/08/2024 12:25, Ryan Roberts wrote: > > On 07/08/2024 19:59, Peter Xu wrote: > >> On Wed, Aug 07, 2024 at 12:18:18PM +0200, David Hildenbrand wrote: > >>> On 07.08.24 10:58, David Hildenbrand wrote: > >>>> On 06.08.24 22:29, Peter Xu wrote: > >>>>> On Tue, Aug 06, 2024 at 06:37:55PM +0200, David Hildenbrand wrote: > >>>>>> On 06.08.24 17:15, Ryan Roberts wrote: > >>>>>>> Hi Peter, David, > >>>>> > >>>>> Hi, Ryan, > >>>>> > >>>>>>> > >>>>>>> syzkaller has found an issue (at least on arm64, but I suspect it will be > >>>>>>> visible on x86_64 too) that triggers the following warning: > >>>>> > >>>>> This is true. I can easily reproduce.. > >>>>> > > [...] > > >> When I'm looking at this specific issue again, it's more than ptes that > >> should need to remove the uffd-wp bit. We have: > >> > >> - pmd/pud/hugetlb in other paths that will need similar care.. > >> > >> - move_page_tables() smartness on HAVE_MOVE_PUD.. where we may need to > >> walk the pmd page removing the bits when necessary.. > >> > >> - more importantly, mremap_userfaultfd_prep() might be too late if it's > >> after moving pgtables.. > >> > >> - [not yet started looking] the mlock issue Ryan mentioned.. > >> > >> Looks like we'll need more things to fix and test.. > >> > >> I wished if I can simply disable UFFD_WP + EVENT_REMAP, but I think even > >> with that, by default when mremap() we should still logically tear down all > >> those uffd-wp bits which is the same as !EVENT_REMAP now.. > >> > >> Let me know if anyone would like to beat me to it on fixing the whole > >> thing, I'd be more than happy.. > > > > Afraid I won't be able to sign up to doing that work. > > > > Otherwise, I'll probably need to postpone > >> the fix of this issue for 1-2 weeks but finish some other things first.. > > I'm not sure if there was any progress on this? We are still seeing the problem > on v6.12-rc1. Hi, Ryan, I haven't yet got free time to look at this, sorry. I confess I didn't prioritize this as high, as I doubt anyone would make real use of it, or hit this issue in real workloads, and it'll even slow down generic workloads even if slightly. Do you want to have a look? It'll be great if so. Or I can try to find some time this month. Thanks, -- Peter Xu