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[2003:cb:c708:1d00:99ec:9656:7475:678d]) by smtp.gmail.com with ESMTPSA id x1-20020adfec01000000b00332cfd83b8dsm15601843wrn.96.2023.11.28.09.55.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Nov 2023 09:55:20 -0800 (PST) Message-ID: <1c79ad05-cb52-4820-b2aa-bbe07ff82b19@redhat.com> Date: Tue, 28 Nov 2023 18:55:18 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 19/27] mm: mprotect: Introduce PAGE_FAULT_ON_ACCESS for mprotect(PROT_MTE) To: Alexandru Elisei , catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev, maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, arnd@arndb.de, akpm@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, mhiramat@kernel.org, rppt@kernel.org, hughd@google.com Cc: pcc@google.com, steven.price@arm.com, anshuman.khandual@arm.com, vincenzo.frascino@arm.com, eugenis@google.com, kcc@google.com, hyesoo.yu@samsung.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org References: <20231119165721.9849-1-alexandru.elisei@arm.com> <20231119165721.9849-20-alexandru.elisei@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 19.11.23 17:57, Alexandru Elisei wrote: > To enable tagging on a memory range, userspace can use mprotect() with the > PROT_MTE access flag. Pages already mapped in the VMA don't have the > associated tag storage block reserved, so mark the PTEs as > PAGE_FAULT_ON_ACCESS to trigger a fault next time they are accessed, and > reserve the tag storage on the fault path. That sounds alot like fake PROT_NONE. Would there be a way to unify hat handling and simply reuse pte_protnone()? For example, could we special case on VMA flags? Like, don't do NUMA hinting in these special VMAs. Then, have something like: if (pte_protnone(vmf->orig_pte)) return handle_pte_protnone(vmf); In there, special case on the VMA flags. I *suspect* that handle_page_missing_tag_storage() stole (sorry :P) some code from the prot_none handling path. At least the recovery path and writability handling looks like it better be located shared in handle_pte_protnone() as well. That might take some magic out of this patch. -- Cheers, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel