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Received: from [50.53.43.113] (helo=[192.168.254.34]) by bombadil.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vVOwz-00000004o6W-06pX; Tue, 16 Dec 2025 06:54:25 +0000 Message-ID: Date: Mon, 15 Dec 2025 22:54:24 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/26] Introduce meminspect To: Eugen Hristev , linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, tglx@linutronix.de, andersson@kernel.org, pmladek@suse.com, corbet@lwn.net, david@redhat.com, mhocko@suse.com Cc: tudor.ambarus@linaro.org, mukesh.ojha@oss.qualcomm.com, linux-arm-kernel@lists.infradead.org, linux-hardening@vger.kernel.org, jonechou@google.com, rostedt@goodmis.org, linux-doc@vger.kernel.org, devicetree@vger.kernel.org, linux-remoteproc@vger.kernel.org, linux-arch@vger.kernel.org, tony.luck@intel.com, kees@kernel.org, Trilok Soni , Kaushal Kumar , Shiraz Hashim , Peter Griffin , stephen.s.brennan@oracle.com, Will McVicker , "stefan.schmidt@linaro.org" References: <20251119154427.1033475-1-eugen.hristev@linaro.org> <5903a8e1-71c6-4546-ac50-35effa078dda@infradead.org> Content-Language: en-US From: Randy Dunlap In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/12/25 11:22 PM, Eugen Hristev wrote: > > > On 12/13/25 08:57, Randy Dunlap wrote: >> Hi, >> >> On 12/12/25 10:48 PM, Eugen Hristev wrote: >>> >>> >>> On 11/19/25 17:44, Eugen Hristev wrote: >>>> meminspect is a mechanism which allows the kernel to mark specific memory >>>> areas for memory dumping or specific inspection, statistics, usage. >>>> Once regions are marked, meminspect keeps an internal list with the regions >>>> in a dedicated table. >>> >>> [...] >>> >>> >>>> I will present this version at Plumbers conference in Tokyo on December 13th: >>>> https://lpc.events/event/19/contributions/2080/ >>>> I am eager to discuss it there face to face. >>> >>> Summary of the discussions at LPC talk on Dec 13th: >>> >>> One main idea on the static variables annotation was to do some linker >>> magic, to create a list of variables in the tree, that would be parsed >>> by some script, the addresses and sizes would be then stored into the >>> dedicated section at the script level, without having any C code change. >>> Pros: no C code change, Cons: it would be hidden/masked from the code, >>> easy to miss out, which might lead to people's variables being annotated >>> without them knowing >>> >>> Another idea was to have variables directly stored in a dedicated >>> section which would be added to the table. >>> e.g. static int __attribute(section (...)) nr_irqs; >>> Pros: no more meminspect section Cons: have to keep all interesting >>> variables in a separate section, which might not be okay for everyone. >>> >>> On dynamic memory, the memblock flag marking did not receive any obvious >>> NAKs. >>> >>> On dynamic memory that is bigger in size than one page, as the table >>> entries are registered by virtual address, this would be non-contiguous >>> in physical memory. How is this solved? >>> -> At the moment it's left for the consumer drivers to handle this >>> situation. If the region is a VA and the size > PAGE_SIZE, then the >>> driver needs to handle the way it handles it. Maybe the driver that >>> parses the entry needs to convert it into multiple contiguous entries, >>> or just have virtual address is enough. The inspection table does not >>> enforce or limit the entries to contiguous entries only. >>> >>> On the traverse/notifier system, the implementation did not receive any >>> obvious NAKs >>> >>> General comments: >>> >>> Trilok Soni from Qualcomm mentioned they will be using this into their >>> software deliveries in production. >>> >>> Someone suggested to have some mechanism to block specific data from >>> being added to the inspection table as being sensitive non-inspectable >>> data. >>> [Eugen]: Still have to figure out how that could be done. Stuff is not >>> being added to the table by default. >>> >>> Another comment was about what use case there is in mind, is this for >>> servers, or for confidential computing, because each different use case >>> might have different requirements, like ignoring some regions is an >>> option in one case, but bloating the table in another case might not be >>> fine. >>> [Eugen]: The meminspect scenario should cover all cases and not be too >>> specific. If it is generic enough and customizable enough to care for >>> everyone's needs then I consider it being a success. It should not >>> specialize in neither of these two different cases, but rather be >>> tailored by each use case to provide the mandatory requirements for that >>> case. >>> >>> Another comment mentioned that this usecase does not apply to many >>> people due to firmware or specific hardware needed. >>> [Eugen]: one interesting proposed usecase is to have a pstore >>> driver/implementation that would traverse the inspection table at panic >>> handler time, then gather data from there to store in the pstore >>> (ramoops, mtdoops or whatever backend) and have it available to the >>> userspace after reboot. This would be a nice use case that does not >>> require firmware nor specific hardware, just pstore backend support. >>> >>> Ending note was whether this implementation is going in a good direction >>> and what would be the way to having it moving upstream. >>> >>> Thanks everyone who attended and came up with ideas and comments. >>> There are a few comments which I may have missed, so please feel free to >>> reply to this email to start a discussion thread on the topic you are >>> interested in. >>> >>> Eugen >>> >> >> Maybe you or someone else has already mentioned this. If so, sorry I missed it. >> >> How does this compare or contrast to VMCOREINFO? >> >> thanks. > > This inspection table could be created in an VMCOREINFO way, the patch > series here[1] is something that would fit it best . > > The drawbacks are : > some static variables have to be registered to VMCOREINFO in their file > of residence. This means including vmcoreinfo header and adding > functions/code there, and everywhere that would be needed , or , the > variables have to be un-static'ed , which is a no-go. > This received more negative opinions on that particular patch series. > The annotation idea seemed cleaner and simpler, and more generic. > > We could add more and more entries to the vmcoreinfo table, but that > would mean expanding it a lot, which it would maybe defy its purpose, > and be getting too big, especially for the cases where custom drivers > would like to register data. > > How I see it, is that maybe the vmcoreinfo init function, could also > parse the inspection table and create more entries if that is needed. > So somehow memory inspection is a superset or generalization , while > VMCOREINFO is a more particular use case that would fit here. > > Do you think of some better way to integrate the meminspect table into > VMCOREINFO ? No, I just wanted to make sure that you or someone had looked into that. Thanks for your summary. > [1] > https://lore.kernel.org/all/20250912150855.2901211-1-eugen.hristev@linaro.org/ -- ~Randy