linux-kernel - Re: [PATCH v2] vfio-pci: Mask cap zero

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Message-ID: <20200506132633.033cbc2c.cohuck@redhat.com>
Date:   Wed, 6 May 2020 13:26:33 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, cjia@...dia.com
Subject: Re: [PATCH v2] vfio-pci: Mask cap zero

On Tue, 05 May 2020 16:27:01 -0600
Alex Williamson <alex.williamson@...hat.com> wrote:

> The PCI Code and ID Assignment Specification changed capability ID 0
> from reserved to a NULL capability in the v1.1 revision.  The NULL
> capability is defined to include only the 16-bit capability header,
> ie. only the ID and next pointer.  Unfortunately vfio-pci creates a
> map of config space, where ID 0 is used to reserve the standard type
> 0 header.  Finding an actual capability with this ID therefore results
> in a bogus range marked in that map and conflicts with subsequent
> capabilities.  As this seems to be a dummy capability anyway and we
> already support dropping capabilities, let's hide this one rather than
> delving into the potentially subtle dependencies within our map.
> 
> Seen on an NVIDIA Tesla T4.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
>  drivers/vfio/pci/vfio_pci_config.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)

Reviewed-by: Cornelia Huck <cohuck@...hat.com>