Re: [PATCH 1/3] hw/arm/virt: KVM: Probe for KVM_CAP_ARM_VM_IPA_SIZE when creating scratch VM

[Eric Auger]

Hi Marc,

On 8/22/21 4:44 PM, Marc Zyngier wrote:
> Although we probe for the IPA limits imposed by KVM (and the hardware)
> when computing the memory map, we still use the old style '0' when
> creating a scratch VM in kvm_arm_create_scratch_host_vcpu().
>
> On systems that are severely IPA challenged (such as the Apple M1),
> this results in a failure as KVM cannot use the default 40bit that
> '0' represents.
>
> Instead, probe for the extension and use the reported IPA limit
> if available.
>
> Cc: Andrew Jones <drjones@redhat.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric
> ---
>  target/arm/kvm.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index d8381ba224..cc3371a99b 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -70,12 +70,17 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t 
> *cpus_to_try,
>                                        struct kvm_vcpu_init *init)
>  {
>      int ret = 0, kvmfd = -1, vmfd = -1, cpufd = -1;
> +    int max_vm_pa_size;
>  
>      kvmfd = qemu_open_old("/dev/kvm", O_RDWR);
>      if (kvmfd < 0) {
>          goto err;
>      }
> -    vmfd = ioctl(kvmfd, KVM_CREATE_VM, 0);
> +    max_vm_pa_size = ioctl(kvmfd, KVM_CHECK_EXTENSION, 
> KVM_CAP_ARM_VM_IPA_SIZE);
> +    if (max_vm_pa_size < 0) {
> +        max_vm_pa_size = 0;
> +    }
> +    vmfd = ioctl(kvmfd, KVM_CREATE_VM, max_vm_pa_size);
>      if (vmfd < 0) {
>          goto err;
>      }