Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932583AbcCHJV5 (ORCPT ); Tue, 8 Mar 2016 04:21:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:42727 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932244AbcCHJVr (ORCPT ); Tue, 8 Mar 2016 04:21:47 -0500 Date: Tue, 8 Mar 2016 11:21:37 +0200 From: "Michael S. Tsirkin" To: Greg KH Cc: Gabriel Somlo , 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: [RFC PATCH] firmware: qemu_fw_cfg.c: hold ACPI global lock during device access Message-ID: <20160308110716-mutt-send-email-mst@redhat.com> References: <20160307235543.GD2049@HEDWIG.INI.CMU.EDU> <20160308000215.GA11917@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160308000215.GA11917@kroah.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Tue, 08 Mar 2016 09:21:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3162 Lines: 92 On Mon, Mar 07, 2016 at 04:02:15PM -0800, Greg KH wrote: > 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 ACK, except for Gerd's comments below. > > --- > > > > 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 You should include linux/acpi.h if you use this, do not rely on some other header to pull this in. > > + 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. Indeed. In fact include/acpi/platform/aclinux.h already has this code: #ifndef CONFIG_ACPI /* External globals for __KERNEL__, stubs is needed */ #define ACPI_GLOBAL(t,a) #define ACPI_INIT_GLOBAL(t,a,b) /* Generating stubs for configurable ACPICA macros */ #define ACPI_NO_MEM_ALLOCATIONS /* Generating stubs for configurable ACPICA functions */ #define ACPI_NO_ERROR_MESSAGES #undef ACPI_DEBUG_OUTPUT /* External interface for __KERNEL__, stub is needed */ #define ACPI_EXTERNAL_RETURN_STATUS(prototype) \ static ACPI_INLINE prototype {return(AE_NOT_CONFIGURED);} #define ACPI_EXTERNAL_RETURN_OK(prototype) \ static ACPI_INLINE prototype {return(AE_OK);} #define ACPI_EXTERNAL_RETURN_VOID(prototype) \ static ACPI_INLINE prototype {return;} #define ACPI_EXTERNAL_RETURN_UINT32(prototype) \ static ACPI_INLINE prototype {return(0);} #define ACPI_EXTERNAL_RETURN_PTR(prototype) \ static ACPI_INLINE prototype {return(NULL);} #endif /* CONFIG_ACPI */ so it's just a question of testing the return code for AE_NOT_CONFIGURED. -- MST