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

[Eduardo Habkost]

On Thu, Nov 26, 2020 at 10:50:17PM +0100, Alexander Graf 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.
> 
> Signed-off-by: Alexander Graf <agraf@csgraf.de>
> ---
>  hw/arm/virt.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 27dbeb549e..d74053ecd4 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -45,6 +45,7 @@
>  #include "hw/display/ramfb.h"
>  #include "net/net.h"
>  #include "sysemu/device_tree.h"
> +#include "sysemu/hvf.h"
>  #include "sysemu/numa.h"
>  #include "sysemu/runstate.h"
>  #include "sysemu/sysemu.h"
> @@ -1746,6 +1747,14 @@ static void machvirt_init(MachineState *machine)
>      unsigned int smp_cpus = machine->smp.cpus;
>      unsigned int max_cpus = machine->smp.max_cpus;
>  
> +    /*
> +     * On Hypervisor.framework capable systems, we only have 36 bits of PA
> +     * space, which is not enough to fit a 64bit BAR space
> +     */
> +    if (hvf_enabled()) {
> +        vms->highmem = false;
> +    }

Direct checks for *_enabled() are a pain to clean up later when
we add support to new accelerators.  Can't this be implemented as
(e.g.) a AccelClass::max_physical_address_bits field?

> +
>      /*
>       * In accelerated mode, the memory map is computed earlier in kvm_type()
>       * to create a VM with the right number of IPA bits.
> -- 
> 2.24.3 (Apple Git-128)
> 

-- 
Eduardo