From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v2] firmware: qemu_fw_cfg.c: hold ACPI global lock during device access Date: Sun, 3 Apr 2016 15:12:31 +0300 Message-ID: <20160403151028-mutt-send-email-mst@redhat.com> References: <20160308183050.GJ2049@HEDWIG.INI.CMU.EDU> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20160308183050.GJ2049-h65ZQ0r4j6KKUezXOiBB2eW1CriLhL8O@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Gabriel Somlo Cc: Greg KH , robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, pawel.moll-5wv7dgnIgG8@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org, ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org, galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, arnd-r2nGTMty4D4@public.gmane.org, lersek-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, ralf-6z/3iImG2C8G8FEW9MqTrA@public.gmane.org, rmk+kernel-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org, eric-WhKQ6XTQaPysTnJN9+BGXg@public.gmane.org, hanjun.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, zajec5-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, sudeep.holla-5wv7dgnIgG8@public.gmane.org, agross-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org, imammedo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, peter.maydell-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, leif.lindholm-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, kraxel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, ehabkost-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org, stefanha-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, revol-GANU6spQydw@public.gmane.org, matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org, rth-hL46jP5Bxq7R7s880joybQ@public.gmane.org List-Id: devicetree@vger.kernel.org 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 Greg, could you merge this please? I'm rather worried that this goes out without. > --- > > 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