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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id s9-20020a05600c45c900b0040b4fca8620sm5777979wmo.37.2023.11.30.05.43.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Nov 2023 05:43:49 -0800 (PST) Message-ID: Date: Thu, 30 Nov 2023 14:43:48 +0100 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 Cc: Hyesoo Yu , 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> <4e7a4054-092c-4e34-ae00-0105d7c9343c@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 30.11.23 14:32, Alexandru Elisei wrote: > Hi, > > On Thu, Nov 30, 2023 at 01:49:34PM +0100, David Hildenbrand wrote: >>>>> + >>>>> +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). > > I wasn't aware of that, thank you for the information. Then to ensure that the > process doesn't hang by replying the loop indefinitely, I'll migrate the page if > tag storage cannot be reserved. Looking over the code again, I think I can reuse > the same function that migrates tag storage pages out of the MTE VMA (added in > patch #21), so no major changes needed. It's going to be interesting if migrating that page fails because it is pinned :/ -- Cheers, David / dhildenb