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

From: Alexander Graf
Subject: Re: [PATCH 8/8] hw/arm/virt: Disable highmem when on hypervisor.framework
Date: Thu, 26 Nov 2020 23:17:28 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.5.0

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
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 ...


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