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Re: [Qemu-block] [libvirt] [Qemu-devel] Configuring pflash devices for O

From: Peter Maydell
Subject: Re: [Qemu-block] [libvirt] [Qemu-devel] Configuring pflash devices for OVMF firmware
Date: Mon, 28 Jan 2019 13:06:34 +0000

On Mon, 28 Jan 2019 at 12:40, Gerd Hoffmann <address@hidden> 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 :-))

-- PMM

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