From patchwork Tue Apr 9 21:02:54 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13623259 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0D30D15886D; Tue, 9 Apr 2024 21:11:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712697076; cv=none; b=jS2w6PRcnTJZ/Vags1tudmP5mCBo2J67Xh9yDTk8NHE8QfxvcRRX+TFob+onpxv6NwJagBugTDH4ZKbnsUGY7QcBUyjEj7nc+IvPMjtJXz/U/7vh4wpZFleFVA8btZHMuJvtdBfOXx7yxAVf9jjd82CGlV2t4dwqh7xwfLSB73s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712697076; c=relaxed/simple; bh=8L0ERTzAy1BQjOx7mGGCwwAduTWBXdMYWDcECfPN7QY=; h=Message-ID:Date:From:To:Cc:Subject; b=FUiICzqKYXokk8KuS4rQs2Em71o0cmbtISei3DaouI4FM659Vxix357kmEpIZGGCzBnTIA2UOdm9I75l7TzDC0llbW2t6OiSTHehC1cTHJ8LnDmQdhZwHKbkf7r9LD5mVxt0BldSQ668dLvVwwfpPrBdXWW4/Z/V6bNfDBIMfk4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 83FA0C433C7; Tue, 9 Apr 2024 21:11:15 +0000 (UTC) Received: from rostedt by gandalf with local (Exim 4.97) (envelope-from ) id 1ruImt-00000000d1d-0Dhi; Tue, 09 Apr 2024 17:13:51 -0400 Message-ID: <20240409210254.660888920@goodmis.org> User-Agent: quilt/0.67 Date: Tue, 09 Apr 2024 17:02:54 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , linux-mm@kvack.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Peter Zijlstra , Kees Cook , Tony Luck , "Guilherme G. Piccoli" , linux-hardening@vger.kernel.org, Guenter Roeck , Ross Zwisler , wklin@google.com, Vineeth Remanan Pillai , Joel Fernandes , Suleiman Souhlal , Linus Torvalds , Catalin Marinas , Will Deacon Subject: [POC][RFC][PATCH 0/2] pstore/mm/x86: Add wildcard memmap to map pstore consistently Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Add wildcard option of reserving physical memory on kernel command line Background: In ChromeOS, we have 1 MB of pstore ramoops reserved so that we can extract dmesg output and some other information when a crash happens in the field. (This is only done when the user selects "Allow Google to collect data for improving the system"). But there are cases when there's a bug that requires more data to be retrieved to figure out what is happening. We would like to increase the pstore size, either temporarily, or maybe even permanently. The pstore on these devices are at a fixed location in RAM (as the RAM is not cleared on soft reboots nor crashes). The location is chosen by the BIOS (coreboot) and passed to the kernel via ACPI tables on x86. There's a driver that queries for this to initialize the pstore for ChromeOS: See drivers/platform/chrome/chromeos_pstore.c Problem: The problem is that, even though there's a process to change the kernel on these systems, and is done regularly to install updates, the firmware is updated much less frequently. Choosing the place in RAM also takes special care, and may be in a different address for different boards. Updating the size via firmware is a large effort and not something that many are willing to do for a temporary pstore size change. Requirement: Need a way to reserve memory that will be at a consistent location for every boot, if the kernel and system are the same. Does not need to work if rebooting to a different kernel, or if the system can change the memory layout between boots. The reserved memory can not be an hard coded address, as the same kernel / command line needs to run on several different machines. The picked memory reservation just needs to be the same for a given machine, but may be different for different machines. Solution: The solution I have come up with is to introduce a new "memmap=" kernel command line (for x86 and I would like something similar for ARM that uses device tree). As "memmap=" kernel command line parameter takes on several flavors already, I would like to introduce a new one. The "memmap=" kernel parameter is of the format of: memmap=nn[Xss] Where nn is the size, 'X' defines the flavor, and 'ss' usually a parameter to that flavor. The '$' flavor is to reserve physical memory where you could have: memmap=12M$0xb000000 Where 12 megs of memory will be reserved at the address 0xb0000000. This memory will not be part of the memory used by the kernel's memory management system. (e.g. alloc_pages() and kmalloc() will not return memory in that location). I would like to introduce a "wildcard" flavor that is of the format: memmap=nn*align:label Where nn is the size of memory to reserve, the align is the alignment of that memory, and label is the way for other sub-systems to find that memory. This way the kernel command line could have: memmap=12M*4096:oops ramoops.mem_name=oops At boot up, the kernel will search for 12 megabytes in usable memory regions with an alignment of 4096. It will start at the highest regions and work its way down (for those old devices that want access to lower address DMA). When it finds a region, it will save it off in a small table and mark it with the "oops" label. Then the pstore ramoops sub-system could ask for that memory and location, and it will map itself there. This prototype allows for 8 different mappings (which may be overkill, 4 is probably plenty) with 16 byte size to store the label. The table lookup is only available until boot finishes, which means it is only available for builtin code and not for modules. I have tested this and it works for us to solve the above problem. We can update the kernel and command line and increase the size of pstore without needing to update the firmware, or knowing every memory layout of each board. I only tested this locally, it has not been tested in the field. Before doing anything, I am looking for feedback. Maybe I missed something. Perhaps there's a better way. Anyway, this is both a Proof of Concept as well as a Request for Comments. Thanks! Steven Rostedt (Google) (2): mm/x86: Add wildcard '*' option as memmap=nn*align:name pstore/ramoops: Add ramoops.mem_name= command line option ---- arch/x86/kernel/e820.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++ fs/pstore/ram.c | 18 ++++++++++ include/linux/mm.h | 2 ++ mm/memory.c | 7 ++++ 4 files changed, 118 insertions(+)