Re: [PATCH v17 RESEND] pvpanic: pvpanic device driver

[Hu Tao <hutao@cn.fujitsu.com>]

On Fri, May 03, 2013 at 06:59:18PM -0300, Marcelo Tosatti wrote:
> On Fri, May 03, 2013 at 10:47:10AM +0800, Hu Tao wrote:
> > pvpanic device is a qemu simulated device through which guest panic
> > event is sent to host.
> > 
> > Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
> > ---
> >  drivers/platform/x86/Kconfig   |   7 +++
> >  drivers/platform/x86/Makefile  |   2 +
> >  drivers/platform/x86/pvpanic.c | 115 +++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 124 insertions(+)
> >  create mode 100644 drivers/platform/x86/pvpanic.c
> > 
> > diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
> > index 3338437..527ed04 100644
> > --- a/drivers/platform/x86/Kconfig
> > +++ b/drivers/platform/x86/Kconfig
> > @@ -781,4 +781,11 @@ config APPLE_GMUX
> >  	  graphics as well as the backlight. Currently only backlight
> >  	  control is supported by the driver.
> >  
> > +config PVPANIC
> > +	tristate "pvpanic device support"
> > +	depends on ACPI
> > +	---help---
> > +	  This driver provides support for pvpanic device, which is a qemu
> > +	  simulated device through which guest panic event is sent to host.
> > +
> >  endif # X86_PLATFORM_DEVICES
> > diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
> > index ace2b38..ef0ec74 100644
> > --- a/drivers/platform/x86/Makefile
> > +++ b/drivers/platform/x86/Makefile
> > @@ -51,3 +51,5 @@ obj-$(CONFIG_INTEL_OAKTRAIL)	+= intel_oaktrail.o
> >  obj-$(CONFIG_SAMSUNG_Q10)	+= samsung-q10.o
> >  obj-$(CONFIG_APPLE_GMUX)	+= apple-gmux.o
> >  obj-$(CONFIG_CHROMEOS_LAPTOP)	+= chromeos_laptop.o
> > +
> > +obj-$(CONFIG_PVPANIC)           += pvpanic.o
> > diff --git a/drivers/platform/x86/pvpanic.c b/drivers/platform/x86/pvpanic.c
> > new file mode 100644
> > index 0000000..81c95ec
> > --- /dev/null
> > +++ b/drivers/platform/x86/pvpanic.c
> > @@ -0,0 +1,115 @@
> > +/*
> > + *  pvpanic.c - pvpanic Device Support
> > + *
> > + *  Copyright (C) 2013 Fujitsu.
> > + *
> > + *  This program is free software; you can redistribute it and/or modify
> > + *  it under the terms of the GNU General Public License as published by
> > + *  the Free Software Foundation; either version 2 of the License, or
> > + *  (at your option) any later version.
> > + *
> > + *  This program is distributed in the hope that it will be useful,
> > + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + *  GNU General Public License for more details.
> > + *
> > + *  You should have received a copy of the GNU General Public License
> > + *  along with this program; if not, write to the Free Software
> > + *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
> > + */
> > +
> > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/init.h>
> > +#include <linux/types.h>
> > +#include <acpi/acpi_bus.h>
> > +#include <acpi/acpi_drivers.h>
> > +
> > +MODULE_AUTHOR("Hu Tao <hutao@cn.fujitsu.com>");
> > +MODULE_DESCRIPTION("pvpanic device driver");
> > +MODULE_LICENSE("GPL");
> > +
> > +static int pvpanic_add(struct acpi_device *device);
> > +static int pvpanic_remove(struct acpi_device *device);
> > +
> > +static const struct acpi_device_id pvpanic_device_ids[] = {
> > +	{ "QEMU0001", 0},
> > +	{ "", 0},
> > +};
> > +MODULE_DEVICE_TABLE(acpi, pvpanic_device_ids);
> > +
> > +#define PVPANIC_PANICKED	(1 << 0)
> > +
> > +static acpi_handle handle;
> > +
> > +static struct acpi_driver pvpanic_driver = {
> > +	.name =		"pvpanic",
> > +	.class =	"QEMU",
> > +	.ids =		pvpanic_device_ids,
> > +	.ops =		{
> > +				.add =		pvpanic_add,
> > +				.remove =	pvpanic_remove,
> > +			},
> > +	.owner =	THIS_MODULE,
> > +};
> > +
> > +static void
> > +pvpanic_send_event(unsigned int event)
> > +{
> > +	union acpi_object arg;
> > +	struct acpi_object_list arg_list;
> > +
> > +	if (!handle)
> > +		return;
> > +
> > +	arg.type = ACPI_TYPE_INTEGER;
> > +	arg.integer.value = event;
> > +
> > +	arg_list.count = 1;
> > +	arg_list.pointer = &arg;
> > +
> > +	acpi_evaluate_object(handle, "WRPT", &arg_list, NULL);
> > +}
> 
> Is it safe to call acpi_evaluate_object from a panic notifier? For
> example:
> 
> - Has it been confirmed that no code invoked via acpi_evaluate_object can panic() ?

Confirmed.

> - acpi_ex_enter_interpreter grabs a mutex. Is that path ever used?

Unfortunately yes. As I can tell, there are 2 places in the path to grab
a mutex: when searching the namespace for the method, and when executing
the method. I didn't find a non-blocking version of acpi_evaluate_object.