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b=nmR4Y/kfmtn0Wmed73+zC6gl9p+RgdyAlq7iOw/eanf+Cq4YGxcOntSUAUlrVrkD5 /JTdTmJBH8ducDgUDNbg0eR0HP1wSy/cdADfacMkChwWXjmgBDWrcYjgVHWwdhh2Uo xkF6a3gTPxK9Jbio4tKD5k/Sfryr+KE+SAWvRneJ+AgOTTlCUA8r/MMuRFacp3R8TE ZxyFwU/yZDiTSDkyqGSli2izvVpe8HjQlQbTRfoAFvSHjMaNKJ0oqpVgTkpNvPl15p A5FNDAsUrZ9cHAPB5JTK7YZe6vHkD4j/ikMO4P2DXzyeOW5TfaDOUQfJMw5nxsOklg iXmEkqWlbBbQA== Date: Tue, 13 May 2025 21:46:04 +0100 From: Will Deacon To: Ryan Roberts Cc: Catalin Marinas , Pasha Tatashin , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , David Hildenbrand , "Matthew Wilcox (Oracle)" , Mark Rutland , Anshuman Khandual , Alexandre Ghiti , Kevin Brodsky , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+5c0d9392e042f41d45c5@syzkaller.appspotmail.com Subject: Re: [PATCH] arm64/mm: Disable barrier batching in interrupt contexts Message-ID: <20250513204603.GA9866@willie-the-truck> References: <20250512102242.4156463-1-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250512102242.4156463-1-ryan.roberts@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspam-User: X-Rspamd-Queue-Id: B1EEA2000B X-Rspamd-Server: rspam09 X-Stat-Signature: 3iutnyxcspf4y4rkcmbgbdbo68io7xpb X-HE-Tag: 1747169171-374232 X-HE-Meta: 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 h25Rd0br jbR11hymoYpLynw8//8wzIspETz5Y5MjUvvzDqLayG08Nfug9jPpec4puFVXjZr4zEplKPtOpA1jCpoOmjEzkeey/psbNuAxt9ayA1ec8l9tA/Fu6imnALcsKpiBZ6XFMNxzjH6JYqGolhd7QK/CRttVeK2/jJurpo4+xuavW7dsVu9BmrZ0whUMwGt7QUOh/FYm4i1+YWiwYGdOX41kByWvBGzIeEgT3rr3O84pehkBE+Var3Ajcd6a9hcTZqWXrEeBAPNe/gb0Sg/MS607CoYON9VmA/6s2ekrR9pDsLJuDMUvziQLcBOI1prn8ZW5vBjiS 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 Mon, May 12, 2025 at 11:22:40AM +0100, Ryan Roberts wrote: > Commit 5fdd05efa1cd ("arm64/mm: Batch barriers when updating kernel > mappings") enabled arm64 kernels to track "lazy mmu mode" using TIF > flags in order to defer barriers until exiting the mode. At the same > time, it added warnings to check that pte manipulations were never > performed in interrupt context, because the tracking implementation > could not deal with nesting. > > But it turns out that some debug features (e.g. KFENCE, DEBUG_PAGEALLOC) > do manipulate ptes in softirq context, which triggered the warnings. Hmm. Do we also have to worry about the case where a softirq is triggered off the back of a hardirq *and* that hardirq is taken while we're in the middle of e.g. queue_pte_barriers()? In that case, I think we can end up in strange situations, such as having LAZY_MMU_PENDING set when LAZY_MMU is clear, although it looks like things still work even in that case. Will