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([2001:b07:6468:f312:9af8:e5f5:7516:fa89]) by smtp.googlemail.com with ESMTPSA id a2-20020adff7c2000000b003177074f830sm2383424wrq.59.2023.08.31.07.18.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 31 Aug 2023 07:18:49 -0700 (PDT) Message-ID: <122aefbf-0ed7-cdd3-5c0a-3d1c51429598@redhat.com> Date: Thu, 31 Aug 2023 16:18:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [RFC PATCH] Introduce persistent memory pool To: Greg Kroah-Hartman , Stanislav Kinsburskii Cc: Stanislav Kinsburskii , Derek Kiernan , Dragan Cvetic , Arnd Bergmann , Wei Liu , "K. Y. Srinivasan" , Madhavan Venkataraman , Anthony Yznaga , "Mike Rapoport (IBM)" , James Gowans , Anirudh Rayabharam , Jinank Jain , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <64e7cbf7.050a0220.114c7.b70dSMTPIN_ADDED_BROKEN@mx.google.com> <2023082506-enchanted-tripping-d1d5@gregkh> <64e8f6dd.050a0220.edb3c.c045SMTPIN_ADDED_BROKEN@mx.google.com> <2023082633-magnetize-cupcake-accc@gregkh> <64ea25cd.650a0220.642cc.50e6SMTPIN_ADDED_BROKEN@mx.google.com> <2023082620-saint-petition-bb89@gregkh> <64ea3699.170a0220.13ee0.5c3aSMTPIN_ADDED_BROKEN@mx.google.com> <2023082619-puzzling-viewable-fa69@gregkh> From: Paolo Bonzini In-Reply-To: <2023082619-puzzling-viewable-fa69@gregkh> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: CF32820020 X-Stat-Signature: xt8myjmg76dwp4wc9amuwqo9b5j1onr5 X-Rspam-User: X-HE-Tag: 1693491533-726884 X-HE-Meta: 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 TPG3RraN oeJHbUKoY4Km4nOwXWOo8WySrN8OU+BWrnITus7R2nQG9qo6u4Js8BUx46lxwcpHfuUY/Ex8NS1ddnfGSFpErXjrkyqbGc32k5LeDX72Mive+ZSIebKzjY2aasDhTBDalvO8bl2Ua0lfWeBUHK9Yivnd3EEMYnQRLpfb1VNeTUlRYmjbrfSf2Lf79aI/p0iOeRUNU7ZrDbYKdLxoH7GnoqUMQisVYUFn3/sy8qMZNO/ga3fLg+OBAzVA/zwp02nrqI8z1r0Na7Gtmzp7AQoSceNqxYT09Imev1qzV6WrfmTfmacAf+BUZtKa37tk2N63u4gJriel7xknPN4bjXKvicxV7ghxnF4e8wvxwRLYaXe+hiaJ5KsTbJtHGeDg5SyKP6NL2Udq+3zg3czBbkSPeXHLJI3Ffe1cYj1Yt 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: On 8/26/23 22:04, Greg Kroah-Hartman wrote: >> Yeah, I guess the "ABI" word in misleading here, especially the first >> letter. I mean something else: the old kernel/new kernel. >> This persistent memory pool (its metadata) is supposed to be passed >> across kexec with the data. That is probably the main difference in >> comparison to pmem or cma. >> Since the header can change its format between kernels, there should be >> a way to identify it. > > Ah. Hah, that's crazy, and it's never going to work, you need to just > test the version of the kernel that the image was created for (you have > that in the kernel already) and verify that it is the same before > loading the new one. > > That way you never have to worry about any "version number", it's just > the kernel specific version number instead. Checking the version of the kernel is not enough because you want to support kexec to a newer kernel. I agree though that a version number is not needed. In the end this is just like a filesystem and you'd better keep it backwards compatible. If you think you might need an extra field in the header, you have to leave some padding and add a "flags" field that right now is always zero. Or something like that. Paolo