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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 1vVP2w-00000004ojt-3TS1; Tue, 16 Dec 2025 07:00:34 +0000 Message-ID: <93682055-4a6d-4098-b74f-afef735d1699@infradead.org> Date: Mon, 15 Dec 2025 23:00:33 -0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/26] Introduce meminspect From: Randy Dunlap 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, linux-debuggers@vger.kernel.org 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 In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/15/25 10:54 PM, Randy Dunlap wrote: > > > 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. Although you copied Stephen Brennan on this, I think it would be a good idea to copy the linux-debuggers@vger.kernel.org mailing list also to see if there are any other comments about it. [now done] >> [1] >> https://lore.kernel.org/all/20250912150855.2901211-1-eugen.hristev@linaro.org/ > -- ~Randy