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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id bd22-20020a05600c1f1600b004090798d29csm1977198wmb.15.2023.11.30.04.49.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Nov 2023 04:49:36 -0800 (PST) Message-ID: <4e7a4054-092c-4e34-ae00-0105d7c9343c@redhat.com> Date: Thu, 30 Nov 2023 13:49:34 +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 , Hyesoo Yu Cc: 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, pcc@google.com, steven.price@arm.com, anshuman.khandual@arm.com, vincenzo.frascino@arm.com, eugenis@google.com, kcc@google.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> <20231129092725.GD2988384@tiffany> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: s7h81jenhmp84o747esxknhegzapmwo9 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 353BAA0019 X-Rspam-User: X-HE-Tag: 1701348582-636977 X-HE-Meta: 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 q6q9JA5j 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 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: >>> + >>> +out_retry: >>> + put_page(page); >>> + if (vmf->flags & FAULT_FLAG_VMA_LOCK) >>> + vma_end_read(vma); >>> + if (fault_flag_allow_retry_first(vmf->flags)) { >>> + err = VM_FAULT_RETRY; >>> + } else { >>> + /* Replay the fault. */ >>> + err = 0; >> >> Hello! >> >> Unfortunately, if the page continues to be pinned, it seems like fault will continue to occur. >> I guess it makes system stability issue. (but I'm not familiar with that, so please let me know if I'm mistaken!) >> >> How about migrating the page when migration problem repeats. > > Yes, I had the same though in the previous iteration of the series, the > page was migrated out of the VMA if tag storage couldn't be reserved. > > Only short term pins are allowed on MIGRATE_CMA pages, so I expect that the > pin will be released before the fault is replayed. Because of this, and > because it makes the code simpler, I chose not to migrate the page if tag > storage couldn't be reserved. There are still some cases that are theoretically problematic: vmsplice() can pin pages forever and doesn't use FOLL_LONGTERM yet. All these things also affect other users that rely on movability (e.g., CMA, memory hotunplug). -- Cheers, David / dhildenb