linux-kernel - Re: [RFC PATCH 2/3] vfio/hisilicon: register the driver to vfio

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Date:   Thu, 13 May 2021 10:44:22 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     liulongfang <liulongfang@...wei.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>, cohuck@...hat.com,
        linux-kernel@...r.kernel.org, linuxarm@...neuler.org
Subject: Re: [RFC PATCH 2/3] vfio/hisilicon: register the driver to vfio

On Thu, May 13, 2021 at 10:08:28AM +0800, liulongfang wrote:
> On 2021/5/12 20:10, Jason Gunthorpe wrote:
> > On Wed, May 12, 2021 at 04:39:43PM +0800, liulongfang wrote:
> > 
> >> Therefore, this method of limiting the length of the BAR
> >> configuration space can prevent unsafe operations of the memory.
> > 
> > The issue is DMA controlled by the guest accessing the secure BAR
> > area, not the guest CPU.
> > 
> > Jason
> > .
> > 
> This secure BAR area is not presented to the Guest,
> which makes it impossible for the Guest to obtain the secure BAR area
> when establishing the DMA mapping of the configuration space.
> If the DMA controller accesses the secure BAR area, the access will
> be blocked by the SMMU.

There are scenarios where this is not true.

At a minimum the mdev driver should refuse to work in those cases.

Jason