Date:	Fri, 5 Jun 2015 13:05:54 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Eric Auger <eric.auger@...aro.org>
Cc:	eric.auger@...com,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, alex.williamson@...hat.com,
	b.reynal@...tualopensystems.com, Alexander Graf <agraf@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Linaro Patches <patches@...aro.org>
Subject: Re: [PATCH v2 0/4] VFIO platform reset

On Fri, Jun 5, 2015 at 10:06 AM, Eric Auger <eric.auger@...aro.org> 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 general, shouldn't it just be a requirement that the drivers handle
this condition. You have the same problem with firmware/bootloaders
leaving h/w not in reset state or kexec'ing to a new kernel.

Rob

> 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 vfio reset modules (in-kernel or external). The vfio-platform
> driver holds a whitelist of implemented triplets (compat string, module
> name, 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-rc6-reset-v2
>
> History:
> 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    | 98 ++++++++++++++++++++++
>  drivers/vfio/platform/vfio_platform_common.c       | 75 ++++++++++++++++-
>  drivers/vfio/platform/vfio_platform_private.h      | 14 ++++
>  7 files changed, 200 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
>
> --
> 1.9.1
>
>
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