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From: Peter Maydell <peter.maydell@linaro.org>
Date: Mon, 28 Jan 2019 13:06:34 +0000
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Subject: Re: [Qemu-devel] [libvirt] Configuring pflash devices for OVMF
 firmware
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>, Libvirt <libvir-list@redhat.com>, Peter Krempa <pkrempa@redhat.com>, =?UTF-8?B?TMOhc3psw7Mgw4lyc2Vr?= <lersek@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, Qemu-block <qemu-block@nongnu.org>

On Mon, 28 Jan 2019 at 12:40, Gerd Hoffmann <kraxel@redhat.com> wrote:
> The tricky part is the access control here.  On physical hardware you
> typically have one flash rom, say 16M below 4G (on x86).
>
> Our pflash device doesn't allow to define multiple regions, so we use
> multiple pflash devices instead, each with different access permissions
> (code vs. vars).  Because of that they are more dynamic than they are on
> phyiscal hardware, x86 sizes them according to the size of the firmware
> images (arm is easier here, we have fixed size and location no matter
> how big the firmware images are).
>
> So I think the options we have are:
>   (a) leave pflash as-is, which pretty much implies physaddr and size
>       must be user-configurable.
>   (b) add support for multiple regions to pflash, so one can attach
>       multiple blockdev at different offsets to a single pflash device.

The latter makes more sense to me -- we should model what the
hardware actually has, because the guest can tell the difference.
(Migration compat is left as an exercise for the reader :-))

thanks
-- PMM