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[46.139.12.213]) by smtp.gmail.com with ESMTPSA id v132sm12245695wme.20.2019.02.11.04.06.51 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 11 Feb 2019 04:06:52 -0800 (PST) Date: Mon, 11 Feb 2019 13:06:50 +0100 From: Ingo Molnar To: Juergen Gross Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, linux-mm@kvack.org, boris.ostrovsky@oracle.com, sstabellini@kernel.org, hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de Subject: Re: [PATCH v2 1/2] x86: respect memory size limiting via mem= parameter Message-ID: <20190211120650.GA74879@gmail.com> References: <20190130082233.23840-1-jgross@suse.com> <20190130082233.23840-2-jgross@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190130082233.23840-2-jgross@suse.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Juergen Gross wrote: > When limiting memory size via kernel parameter "mem=" this should be > respected even in case of memory made accessible via a PCI card. > > Today this kind of memory won't be made usable in initial memory > setup as the memory won't be visible in E820 map, but it might be > added when adding PCI devices due to corresponding ACPI table entries. > > Not respecting "mem=" can be corrected by adding a global max_mem_size > variable set by parse_memopt() which will result in rejecting adding > memory areas resulting in a memory size above the allowed limit. So historically 'mem=xxxM' was a way to quickly limit RAM. If PCI devices had physical mmio memory areas above this range, we'd still expect them to work - the option was really only meant to limit RAM. So I'm wondering what the new logic is here - why should an iomem resource from a PCI device be ignored? It's a completely separate area that might or might not be enumerated in the e820 table - the only requirement we have here I think is that it not overlap RAM areas or each other (obviously). So if I understood this new restriction you want mem= to imply, devices would start failing to initialize on bare metal when mem= is used? Thanks, Ingo