Re: [PATCH 8/8] hw/arm/virt: Disable highmem when on hypervisor.framework

[Alexander Graf]

On 26.11.20 22:54, Peter Maydell wrote:
> On Thu, 26 Nov 2020 at 21:36, Alexander Graf <agraf@csgraf.de> wrote:
> > The Apple M1 only supports up to 36 bits of physical address space. That
> > means we can not fit the 64bit MMIO BAR region into our address space.
> >
> > To fix this, let's not expose a 64bit MMIO BAR region when running on
> > Apple Silicon.
> >
> > I have not been able to find a way to enumerate that easily, so let's
> > just assume we always have that little PA space on hypervisor.framework
> > systems.
> If you have direct access to the host ID_AA64MMFR0_EL1 you can look
> at the PARange field; otherwise start a stunt VM and look at its
> ID_AA64MMFR0_EL1.PARange (this is what we do for KVM to query various
> things about the VM's capabilities/ID regs).


When I tried, I couldn't fetch IID_AA64MMFR0_EL1 as sysreg via hvf.

Are you suggesting that on boot, we start a tiny mini-VM to enumerate 
the PARange and set highmem based on it? That sounds like absolute 
overkill to me ...


Alex