linux-kernel - Re: [Xen-devel] [PATCH 2/2] xen-pciback: Allow enabling/disabling expansion ROM

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Date:   Mon, 03 Dec 2018 04:01:07 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Marek Marczykowski" <marmarek@...isiblethingslab.com>
Cc:     "Dwayne Litzenberger" <dlitz@...tz.net>,
        "Stefano Stabellini" <sstabellini@...nel.org>,
        "xen-devel" <xen-devel@...ts.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
        "Juergen Gross" <jgross@...e.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/2] xen-pciback: Allow
 enabling/disabling expansion ROM

>>> On 02.12.18 at 18:47, <marmarek@...isiblethingslab.com> wrote:
> From: Dwayne Litzenberger <dlitz@...tz.net>
> 
> Newer AMD GPUs store their initialization routines as bytecode on the
> ROM.  This fixes the following initialization error inside the VM when
> doing PCI passthrough:
> 
>     radeon 0000:00:05.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff
>     radeon 0000:00:05.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff
>     [drm:radeon_get_bios [radeon]] *ERROR* Unable to locate a BIOS ROM
>     radeon 0000:00:05.0: Fatal error during GPU init

Isn't it that qemu is supposed to surface the ROM image to guests,
making it unnecessary to allow guests control over the physical
enable bit? Also why would allowing to alter the bit depend on
whether the address portion of the value is non-zero?

Jan