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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37d4b6bd584sm11152917f8f.31.2024.10.14.04.54.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Oct 2024 04:54:30 -0700 (PDT) Message-ID: <2c854e5e-c200-4ed9-bf21-778779af7e5b@redhat.com> Date: Mon, 14 Oct 2024 13:54:27 +0200 Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] memory: extern memory_block_size_bytes and set_memory_block_size_order To: Gregory Price Cc: linux-cxl@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, osalvador@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, akpm@linux-foundation.org, dan.j.williams@intel.com, Jonathan.Cameron@huawei.com, alison.schofield@intel.com, rrichter@amd.com, terry.bowman@amd.com, lenb@kernel.org, dave.jiang@intel.com, ira.weiny@intel.com References: <20241008044355.4325-1-gourry@gourry.net> <20241008044355.4325-2-gourry@gourry.net> <039e8c87-c5da-4469-b10e-e57dd5662cff@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 08.10.24 17:21, Gregory Price wrote: > On Tue, Oct 08, 2024 at 05:02:33PM +0200, David Hildenbrand wrote: >> On 08.10.24 16:51, Gregory Price wrote: >>>>> +int __weak set_memory_block_size_order(unsigned int order) >>>>> +{ >>>>> + return -ENODEV; >>>>> +} >>>>> +EXPORT_SYMBOL_GPL(set_memory_block_size_order); >>>> >>>> I can understand what you are trying to achieve, but letting arbitrary >>>> modules mess with this sounds like a bad idea. >>>> >>> >>> I suppose the alternative is trying to scan the CEDT from inside each >>> machine, rather than the ACPI driver? Seems less maintainable. >>> >>> I don't entirely disagree with your comment. I hummed and hawwed over >>> externing this - hence the warning in the x86 machine. >>> >>> Open to better answers. >> >> Maybe an interface to add more restrictions on the maximum size might be >> better (instead of setting the size/order, you would impose another upper >> limit). > > That is effectively what set_memory_block_size_order is, though. Once > blocks are exposed to the allocators, its no longer safe to change the > size (in part because it was built assuming it wouldn't change, but I > imagine there are other dragons waiting in the shadows to bite me). Yes, we must run very early. How is this supposed to interact with code like set_block_size() that also calls set_memory_block_size_order() on UV systems (assuming there will be CXL support sooner or later?)? > > So this would basically amount to a lock-bit being set in the architecture, > beyond which block size can no longer be changed and a big ol' splat > can be generated that says "NO TOUCH". > >> Just imagine having various users of such an interface .. > > I don't wanna D: Right, and it also doesn't make sense as explained in my other comment: this should never apply to loaded modules. :) -- Cheers, David / dhildenb