linux-kernel - Re: [PATCH v4 0/4] VFIO platform reset

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Message-ID: <55DEFAFE.3000909@linaro.org>
Date:	Thu, 27 Aug 2015 13:56:46 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	eric.auger@...com, linux-arm-kernel@...ts.infradead.org,
	b.reynal@...tualopensystems.com, alex.williamson@...hat.com
CC:	linux-kernel@...r.kernel.org, patches@...aro.org,
	christoffer.dall@...aro.org
Subject: Re: [PATCH v4 0/4] VFIO platform reset

Hi Marc,

I tested the series on Calxeda Midway with VFIO use case. Also reviewed
it again without finding anything new.

Tested-by: Eric Auger <eric.auger@...aro.org>
Reviewed-by: Eric Auger <eric.auger@...aro.org>

Best Regards

Eric

On 06/15/2015 11:09 AM, Eric Auger wrote:
> In situations where the userspace driver is stopped abnormally and the
> VFIO platform device is released, the assigned HW device currently is
> left running. As a consequence the HW device might continue issuing IRQs
> and performing DMA accesses.
> 
> On release, no physical IRQ handler is setup anymore. Also the DMA buffers
> are unmapped leading to IOMMU aborts. So there is no serious consequence.
> 
> However when assigning that HW device again to another userspace driver,
> this latter might face some unexpected IRQs and DMA accesses, which are
> the result of the previous assignment.
> 
> In virtualization use-case, a VM newly granted with that HW device may be
> impacted by the assignment of that device to a previous VM:
> - IRQs may be injected very early when booting the new guest, even before
>   the guest driver has initialized leading to possible driver state
>   inconsistency.
> - DMA accesses may hit the newly mapped VM address space at addresses that
>   may jeopardize the integrity of the newly installed VM.
> 
> Obviously the criticity depends on the assigned HW device.
> 
> As opposed to PCI, there is no standard mechanism to reset the platform
> device.
> 
> This series proposes to implement device specific reset functions in
> separate in-kernel vfio reset modules. The vfio-platform driver holds
> a whitelist of implemented triplets (compat string, module name,
> reset function name). When the vfio-platform driver is probed it identifies
> the fellow reset module/function matching the compat string of the
> device, if any, and forces the load of this reset module.
> 
> A first reset module is provided: the vfio-platform-calxedaxgmac
> module which implements a basic reset for the Calxeda xgmac.
> 
> The series can be found at
> https://git.linaro.org/people/eric.auger/linux.git/shortlog/refs/heads/v4.1-rc8-reset-v4
> 
> History:
> v3 -> v4:
> - fix the commit message of "VFIO: platform: add reset struct and lookup table"
> 
> v2 -> v3:
> - remove void module_init/exit functions in calxeda reset module
> - remove enum vfio_platform_reset_type
> - for reset lookup, use ARRAY_SIZE
> - in reset put use symbol_put_addr
> 
> v1 -> v2:
> - much simplified compared to v1 although principle of external modules is
>   kept: removed mechanism of dynamic registration of reset functions
> - list is replaced by whitelist lookup table
> - name of the reset function also stored in the lookup table
> - autoload of reset modules
> 
> RFC -> PATCH v1:
> - solution now based on a lookup list instead of specialized driver
> 
> 
> Eric Auger (4):
>   VFIO: platform: add reset struct and lookup table
>   VFIO: platform: add reset callback
>   VFIO: platform: populate the reset function on probe
>   VFIO: platform: Calxeda xgmac reset module
> 
>  drivers/vfio/platform/Kconfig                      |  2 +
>  drivers/vfio/platform/Makefile                     |  2 +
>  drivers/vfio/platform/reset/Kconfig                |  7 ++
>  drivers/vfio/platform/reset/Makefile               |  5 ++
>  .../platform/reset/vfio_platform_calxedaxgmac.c    | 86 ++++++++++++++++++++++
>  drivers/vfio/platform/vfio_platform_common.c       | 60 ++++++++++++++-
>  drivers/vfio/platform/vfio_platform_private.h      |  7 ++
>  7 files changed, 166 insertions(+), 3 deletions(-)
>  create mode 100644 drivers/vfio/platform/reset/Kconfig
>  create mode 100644 drivers/vfio/platform/reset/Makefile
>  create mode 100644 drivers/vfio/platform/reset/vfio_platform_calxedaxgmac.c
> 

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