linux-kernel - Re: [PATCH v3 1/4] VFIO: platform: add reset struct and lookup table

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Message-ID: <557AE172.5010302@linaro.org>
Date:	Fri, 12 Jun 2015 15:41:06 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	eric.auger@...com, linux-arm-kernel@...ts.infradead.org,
	b.reynal@...tualopensystems.com, linux-kernel@...r.kernel.org,
	patches@...aro.org, christoffer.dall@...aro.org
Subject: Re: [PATCH v3 1/4] VFIO: platform: add reset struct and lookup table

Hi Alex,
On 06/11/2015 11:11 PM, Alex Williamson wrote:
> On Thu, 2015-06-11 at 14:08 +0200, Eric Auger wrote:
>> This patch introduces the vfio_platform_reset_combo struct that
>> stores all the information useful to handle the reset modality:
>> compat string, name of the reset function, name of the module that
>> implements the reset function. A lookup table of such structures
>> is added, currently containing a single sentinel element. A new
>> type field is added in vfio_platform_device to store what kind of
>> reset is associated to the device, if any.
> 
> The commit log no longer matches the code.
yes indeed missed that.
> 
> The only other thing I'm struggling with in this series is that in 0/4
> you suggest that the reset modules can be in-kernel or external, but
> we're making a static list here, so there's really no support for
> random, user-provided reset modules.  So are we missing the mark on the
> requirements?

Well personally I do not have a MUST HAVE requirement for that feature.
My main requirement was to find a way to stop DMA/IRQ transfers
programmed by a previous VM potentially jeopardizing the integrity of a
second VM.
> 
> One way I thought you could achieve your requirement would be if we did
> away with the lookup table and looked for the module and function using
> a pre-defined transform on the compat ID.  For instance, a compat ID of
> "calxeda,hb-xgmac" would automatically request a module named
> "vfio-platform-reset-calxedahb-xgmac" and look for a symbol of the same
> name for the reset function (I wonder if we can actually have a module
> and symbol of the same name).
I just tried and it works
  It seems fairly safe since an external
> module would need to be explicitly placed in the search path for the
> userspace module loader.
we talked together with Christoffer about such a technique at the very
beginning and he was not very fond of it, advising an approach using a
defined API.
> 
> Otherwise the table would need to become a list, the external module
> would need to be manually loaded, and the module_init() would need to
> register an entry on that list.
Isn't it what I attempted to do in v2 or do you mean something else?

Having a whitelist brings the benefit to know which devices really are
used with vfio-platform (besides some devices may not need any reset
module). I don't know yet whether this is something that may slow down
the adoption.

Personally I would keep it as is for now and see how it gets used and
whether users complain, ...

If you agree I will respin just reworking the commit message.

Best Regards

Eric

  Thanks,



> 
> Alex
> 
>> Signed-off-by: Eric Auger <eric.auger@...aro.org>
>>
>> ---
>>
>> v2 -> v3:
>> - add const in struct vfio_platform_reset_combo
>> - remove enum vfio_platform_reset_type
>>
>> v2: creation
>> ---
>>  drivers/vfio/platform/vfio_platform_common.c  | 3 +++
>>  drivers/vfio/platform/vfio_platform_private.h | 6 ++++++
>>  2 files changed, 9 insertions(+)
>>
>> diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
>> index abcff7a..611597e 100644
>> --- a/drivers/vfio/platform/vfio_platform_common.c
>> +++ b/drivers/vfio/platform/vfio_platform_common.c
>> @@ -25,6 +25,9 @@
>>  
>>  static DEFINE_MUTEX(driver_lock);
>>  
>> +static const struct vfio_platform_reset_combo reset_lookup_table[] = {
>> +};
>> +
>>  static int vfio_platform_regions_init(struct vfio_platform_device *vdev)
>>  {
>>  	int cnt = 0, i;
>> diff --git a/drivers/vfio/platform/vfio_platform_private.h b/drivers/vfio/platform/vfio_platform_private.h
>> index 5d31e04..9e37b9f 100644
>> --- a/drivers/vfio/platform/vfio_platform_private.h
>> +++ b/drivers/vfio/platform/vfio_platform_private.h
>> @@ -69,6 +69,12 @@ struct vfio_platform_device {
>>  	int	(*get_irq)(struct vfio_platform_device *vdev, int i);
>>  };
>>  
>> +struct vfio_platform_reset_combo {
>> +	const char *compat;
>> +	const char *reset_function_name;
>> +	const char *module_name;
>> +};
>> +
>>  extern int vfio_platform_probe_common(struct vfio_platform_device *vdev,
>>  				      struct device *dev);
>>  extern struct vfio_platform_device *vfio_platform_remove_common
> 
> 
> 

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