From patchwork Fri Feb 25 15:55:52 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexander Graf X-Patchwork-Id: 12760517 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3928EC433EF for ; Fri, 25 Feb 2022 15:56:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239024AbiBYP45 (ORCPT ); Fri, 25 Feb 2022 10:56:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41082 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237999AbiBYP44 (ORCPT ); Fri, 25 Feb 2022 10:56:56 -0500 Received: from smtp-fw-80007.amazon.com (smtp-fw-80007.amazon.com [99.78.197.218]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 237941D8A82; Fri, 25 Feb 2022 07:56:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1645804584; x=1677340584; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=SWyuAuqtzwMzh5dusk1nwmrFDHzqhA5gzL9zdrzlblw=; b=nxT/lWz5t/rOIFwsLbsG74pH+PZoN4XgwZdxmqDd8kAeax/xutL6lxDS cvYkqcF3LgwHR7tkop9//Ku0kzu4oEZla5Sa12XN9t9AQk4XIPZ3gMXwG 0Rf1aaaUis3J5qQ7WInRsNFFF/2/JA/VrCVySaPUHVesqd/1WjHvJaWPC Y=; X-IronPort-AV: E=Sophos;i="5.90,136,1643673600"; d="scan'208";a="66236117" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO email-inbound-relay-iad-1d-9a235a16.us-east-1.amazon.com) ([10.25.36.210]) by smtp-border-fw-80007.pdx80.corp.amazon.com with ESMTP; 25 Feb 2022 15:56:06 +0000 Received: from EX13MTAUWC002.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1d-9a235a16.us-east-1.amazon.com (Postfix) with ESMTPS id DEFF381488; Fri, 25 Feb 2022 15:56:02 +0000 (UTC) Received: from EX13D20UWC001.ant.amazon.com (10.43.162.244) by EX13MTAUWC002.ant.amazon.com (10.43.162.240) with Microsoft SMTP Server (TLS) id 15.0.1497.28; Fri, 25 Feb 2022 15:56:02 +0000 Received: from u79c5a0a55de558.ant.amazon.com (10.43.160.203) by EX13D20UWC001.ant.amazon.com (10.43.162.244) with Microsoft SMTP Server (TLS) id 15.0.1497.28; Fri, 25 Feb 2022 15:56:00 +0000 From: Alexander Graf To: CC: , Len Brown , "Rafael J. Wysocki" , "Jason A . Donenfeld" , "Greg KH" , , Subject: [PATCH] ACPI: bus: Match first 9 bytes of device IDs Date: Fri, 25 Feb 2022 16:55:52 +0100 Message-ID: <20220225155552.30636-1-graf@amazon.com> X-Mailer: git-send-email 2.28.0.394.ge197136389 MIME-Version: 1.0 X-Originating-IP: [10.43.160.203] X-ClientProxiedBy: EX13D16UWC004.ant.amazon.com (10.43.162.72) To EX13D20UWC001.ant.amazon.com (10.43.162.244) Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org We create a list of ACPI "PNP" IDs which contains _HID, _CID and CLS entries of the respective devices. However, we squeeze them into struct acpi_device_id which only has 9 bytes space to store the identifier based on the ACPI spec: """ A _HID object evaluates to either a numeric 32-bit compressed EISA type ID or a string. If a string, the format must be an alphanumeric PNP or ACPI ID with no asterisk or other leading characters. A valid PNP ID must be of the form "AAA####" where A is an uppercase letter and # is a hex digit. A valid ACPI ID must be of the form "NNNN####" where N is an uppercase letter or a digit ('0'-'9') and # is a hex digit. This specification reserves the string "ACPI" for use only with devices defined herein. It further reserves all strings representing 4 HEX digits for exclusive use with PCI-assigned Vendor IDs. """ While most people adhere to the ACPI specs, Microsoft decided that its VM Generation Counter device [1] should only be identifiable by _CID with an value of "VM_Gen_Counter" - longer than 9 characters. To still allow device drivers to match identifiers that exceed the 9 byte limit, without wasting memory for the unlikely case that you have long identifiers, let's match only the first 9 characters of the identifier. This patch is a prerequisite to add support for VMGenID in Linux [2]. [1] https://download.microsoft.com/download/3/1/C/31CFC307-98CA-4CA5-914C-D9772691E214/VirtualMachineGenerationID.docx [2] https://lore.kernel.org/lkml/20220225124848.909093-1-Jason@zx2c4.com/ Signed-off-by: Alexander Graf --- Alternatives to the approach above would be: 1) Always set id[8] = '\0' in acpi_add_id() 2) Allocate the id in struct acpi_device_id dynamically I'm happy to explore option 1 instead if people believe it's cleaner. Option 2 on the other hand seems overkill for the issue at hand. We don't have a lot of devices that exceed the 8 character threshold, so chance of collision is quite small. On the other hand, the extra overhead of maintaining the string allocation dynamically will quickly become a headache. --- drivers/acpi/bus.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c index 07f604832fd6..aba93171739f 100644 --- a/drivers/acpi/bus.c +++ b/drivers/acpi/bus.c @@ -829,7 +829,7 @@ static bool __acpi_match_device(struct acpi_device *device, /* First, check the ACPI/PNP IDs provided by the caller. */ if (acpi_ids) { for (id = acpi_ids; id->id[0] || id->cls; id++) { - if (id->id[0] && !strcmp((char *)id->id, hwid->id)) + if (id->id[0] && !strncmp((char *)id->id, hwid->id, ACPI_ID_LEN)) goto out_acpi_match; if (id->cls && __acpi_match_device_cls(id, hwid)) goto out_acpi_match;