From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Subject: Re: [RFC PATCH] firmware: qemu_fw_cfg.c: hold ACPI global lock during device access Date: Mon, 7 Mar 2016 16:02:15 -0800 Message-ID: <20160308000215.GA11917@kroah.com> References: <20160307235543.GD2049@HEDWIG.INI.CMU.EDU> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20160307235543.GD2049-h65ZQ0r4j6KKUezXOiBB2eW1CriLhL8O@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Gabriel Somlo Cc: "Michael S. Tsirkin" , 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: linux-api@vger.kernel.org On Mon, Mar 07, 2016 at 06:55:43PM -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 > --- > > 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); Why not fix up the ACPI api to not require #ifdef here? It should be added to a .h file somewhere instead. > + 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); Same here. thanks, greg k-h