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Re: [RFC PATCH 2/2] hw/arm/raspi: Restrict BCM2835 / BCM2836 SoC to TCG

From: Peter Maydell
Subject: Re: [RFC PATCH 2/2] hw/arm/raspi: Restrict BCM2835 / BCM2836 SoC to TCG
Date: Tue, 2 Feb 2021 12:28:39 +0000

On Mon, 1 Feb 2021 at 08:18, Luc Michel <luc@lmichel.fr> wrote:
> On 16:14 Sun 31 Jan     , Philippe Mathieu-Daudé wrote:
> > KVM requires the target cpu to be at least ARMv8 architecture
> > (support on ARMv7 has been dropped in commit 82bf7ae84ce:
> > "target/arm: Remove KVM support for 32-bit Arm hosts").
> Wow, is there absolutely no way to do that then? What about using an
> ARMv8 and starting in AArch32 mode? Is that possible with KVM? I guess
> it might not be strictly identical as spawning the "real" CPU...

"Support hardware-accelerated emulation of older v7 CPUs" is
not a design goal of the virtualization extensions; you can't
do it. KVM does support having a guest CPU which is AArch32 for EL1,
but that will never be a v7 CPU, because it will be the same as
the host CPU, which will always be v8.

In general I would prefer that we don't try to do stuff to
make KVM kinda-sorta-work on random 32-bit boards by stuffing
in a not-the-right-type CPU, because this increases our
security boundary massively. At the moment we can reasonably
say "only the 'virt' board and one of the Xilinx boards are

-- PMM

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