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

[Marc Zyngier]

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>
---
 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;
     }
-- 
2.30.2