Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753082AbcCIJNf (ORCPT ); Wed, 9 Mar 2016 04:13:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45128 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752911AbcCIJNP (ORCPT ); Wed, 9 Mar 2016 04:13:15 -0500 Date: Wed, 9 Mar 2016 11:13:00 +0200 From: "Michael S. Tsirkin" To: Gabriel Somlo Cc: Greg KH , 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: Re: [PATCH v2] firmware: qemu_fw_cfg.c: hold ACPI global lock during device access Message-ID: <20160309111252-mutt-send-email-mst@redhat.com> References: <20160308183050.GJ2049@HEDWIG.INI.CMU.EDU> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160308183050.GJ2049@HEDWIG.INI.CMU.EDU> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2252 Lines: 68 On Tue, Mar 08, 2016 at 01:30:50PM -0500, Gabriel Somlo wrote: > 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 Acked-by: Michael S. Tsirkin > --- > > Changes since v1: > - no more "#ifdef CONFIG_ACPI"; instead we proceed if > acpi_acquire_global_lock() returns either OK or NOT_CONFIGURED, > and only throw a warning/error message otherwise. > > - didn't get any *negative* feedback from the QEMU crowd, so > this is now a bona-fide "please apply this", rather than just > an RFC :) > > - tested on ACPI-enabled x86_64, and acpi_less ARM (32 and 64 bit) > QEMU VMs (I don't have handy access to an ACPI-enabled ARM VM) > > Thanks much, > --Gabriel > > drivers/firmware/qemu_fw_cfg.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c > index 7bba76c..a44dc32 100644 > --- a/drivers/firmware/qemu_fw_cfg.c > +++ b/drivers/firmware/qemu_fw_cfg.c > @@ -77,12 +77,28 @@ 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) > { > + u32 glk; > + acpi_status status; > + > + /* If we have ACPI, ensure mutual exclusion against any potential > + * device access by the firmware, e.g. via AML methods: > + */ > + status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk); > + if (ACPI_FAILURE(status) && status != AE_NOT_CONFIGURED) { > + /* Should never get here */ > + WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n"); > + memset(buf, 0, count); > + return; > + } > + > 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); > + > + acpi_release_global_lock(glk); > } > > /* clean up fw_cfg device i/o */ > -- > 2.4.3