Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933650AbcCGX4s (ORCPT ); Mon, 7 Mar 2016 18:56:48 -0500 Received: from SMTP.ANDREW.CMU.EDU ([128.2.157.38]:40947 "EHLO smtp.andrew.cmu.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932685AbcCGX4d (ORCPT ); Mon, 7 Mar 2016 18:56:33 -0500 Date: Mon, 7 Mar 2016 18:55:43 -0500 From: Gabriel Somlo To: "Michael S. Tsirkin" , gregkh@linuxfoundation.org, robh+dt@kernel.org, pawel.moll@arm.com, mark.rutland@arm.com, ijc+devicetree@hellion.org.uk, galak@codeaurora.org, arnd@arndb.de, lersek@redhat.com, ralf@linux-mips.org, rmk+kernel@arm.linux.org.uk, eric@anholt.net, hanjun.guo@linaro.org, zajec5@gmail.com, sudeep.holla@arm.com, agross@codeaurora.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, qemu-devel@nongnu.org, imammedo@redhat.com, peter.maydell@linaro.org, leif.lindholm@linaro.org, ard.biesheuvel@linaro.org, pbonzini@redhat.com, kraxel@redhat.com, ehabkost@redhat.com, luto@amacapital.net, stefanha@gmail.com, revol@free.fr, matt@codeblueprint.co.uk, rth@twiddle.net Subject: [RFC PATCH] firmware: qemu_fw_cfg.c: hold ACPI global lock during device access Message-ID: <20160307235543.GD2049@HEDWIG.INI.CMU.EDU> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Clacks-Overhead: GNU Terry Pratchett User-Agent: Mutt/1.5.24 (2015-08-30) X-PMX-Version: 6.0.3.2322014, Antispam-Engine: 2.7.2.2107409, Antispam-Data: 2016.3.7.234817 X-SMTP-Spam-Clean: 8% ( MULTIPLE_RCPTS 0.1, HTML_00_01 0.05, HTML_00_10 0.05, BODYTEXTP_SIZE_3000_LESS 0, BODY_SIZE_2000_2999 0, BODY_SIZE_5000_LESS 0, BODY_SIZE_7000_LESS 0, DATE_TZ_NA 0, FROM_EDU_TLD 0, NO_URI_HTTPS 0, __ANY_URI 0, __CD 0, __CT 0, __CT_TEXT_PLAIN 0, __HAS_FROM 0, __HAS_MSGID 0, __MIME_TEXT_ONLY 0, __MIME_VERSION 0, __MULTIPLE_RCPTS_TO_X5 0, __PHISH_SPEAR_STRUCTURE_1 0, __SANE_MSGID 0, __SUBJ_ALPHA_END 0, __TO_MALFORMED_2 0, __URI_NO_WWW 0, __URI_NS , __USER_AGENT 0) X-SMTP-Spam-Score: 8% Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2006 Lines: 61 Allowing for the future possibility of implementing AML-based (i.e., firmware-triggered) access to the QEMU fw_cfg device, acquire the global ACPI lock when accessing the device on behalf of the guest-side sysfs driver, to prevent any potential race conditions. Suggested-by: Michael S. Tsirkin Signed-off-by: Gabriel Somlo --- Turns out, there *is* a way to acquire a global ACPI lock from within a "random" kernel driver after all. Luckily I have a healthy dose of respect for Michael's opinions :) so I kept circling back through existing kernel sources for an example I can use, and I think this might be it. I'm posting as RFC because I'm not really confident about assessing the likelihood of there ever being a race condition between the kernel fw_cfg sysfs driver and firmware on my own. Obviously Michael has concerns about it, but any additional opinions from the QEMU camp would be much appreciated. Thanks again, --Gabriel drivers/firmware/qemu_fw_cfg.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c index 7bba76c..cc4c27a 100644 --- a/drivers/firmware/qemu_fw_cfg.c +++ b/drivers/firmware/qemu_fw_cfg.c @@ -77,12 +77,26 @@ static inline u16 fw_cfg_sel_endianness(u16 key) static inline void fw_cfg_read_blob(u16 key, void *buf, loff_t pos, size_t count) { +#ifdef CONFIG_ACPI + u32 glk; + int status; + status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk); + if (ACPI_FAILURE(status)) { + /* Should never get here */ + WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n"); + memset(buf, 0, count); + return; + } +#endif mutex_lock(&fw_cfg_dev_lock); iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl); while (pos-- > 0) ioread8(fw_cfg_reg_data); ioread8_rep(fw_cfg_reg_data, buf, count); mutex_unlock(&fw_cfg_dev_lock); +#ifdef CONFIG_ACPI + acpi_release_global_lock(glk); +#endif } /* clean up fw_cfg device i/o */ -- 2.4.3