linux-kernel - Re: [PATCH v2] firmware: qemu_fw_cfg.c: hold ACPI global lock during device access

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Date:	Thu, 17 Mar 2016 14:13:54 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	Gabriel Somlo <somlo@....edu>
Cc:	Greg KH <gregkh@...uxfoundation.org>, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org, arnd@...db.de,
	lersek@...hat.com, ralf@...ux-mips.org,
	rmk+kernel@....linux.org.uk, eric@...olt.net,
	hanjun.guo@...aro.org, zajec5@...il.com, sudeep.holla@....com,
	agross@...eaurora.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	qemu-devel@...gnu.org, imammedo@...hat.com,
	peter.maydell@...aro.org, leif.lindholm@...aro.org,
	ard.biesheuvel@...aro.org, kraxel@...hat.com, ehabkost@...hat.com,
	luto@...capital.net, stefanha@...il.com, revol@...e.fr,
	matt@...eblueprint.co.uk, rth@...ddle.net
Subject: Re: [PATCH v2] firmware: qemu_fw_cfg.c: hold ACPI global lock during
 device access



On 16/03/2016 17:57, Michael S. Tsirkin wrote:
> 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 <mst@...hat.com>
>> Signed-off-by: Gabriel Somlo <somlo@....edu>
> 
> So this patch makes sense of course.
> 
> 
> Given the recent discussion on QEMU mailing list,
> I think there is an additional patch that we need:
> filter the files exposed to userspace by "opt/" prefix.
> 
> This will ensure that we can change all other fw cfg files
> at will without breaking guest scripts.

That makes no sense, all other fw_cfg files are firmware ABI so we
cannot change them anyway.

Paolo